PredictWind, the New Zealand-based company known for providing sailors with weather data, has introduced the PredictCurrent App.

The PredictCurrent App has a quick-view dashboard where sailors can see wind, current, waves and tide height data in one place. Animated maps provide extensive detail on tidal currents, setting what the company calls a new standard in tidal current modeling.

PredictCurrent’s tidal current maps cover 90 percent of the world’s coastlines, according to the company.

“The launch of the PredictCurrent App marks a pivotal moment in marine navigation technology,” Jon Bilger, CEO of PredictWind, stated in a press release. “Our dedicated team has spared no effort in providing mariners worldwide with unparalleled access to comprehensive current data, fostering safer navigation and informed decision-making on the seas. We’re thrilled to be at the forefront of enhancing maritime safety and empowering users with unprecedented insights.”

The app is supported by ultra-high-resolution models that cover areas characterized by complex bathymetry and high tidal flows. This provides accuracy at 100-meter (328-foot) resolution. Supported by a 400-meter (1,312-foot) resolution within 90 kilometers (55 miles) of the coast and a 4-kilometer (2.5-mile) resolution extending up to 600 kilometers (372 miles) offshore, users can see tidal flows anywhere in the world.

Backed by PredictWind forecasts, the app also provides marine weather forecasts in a table format, including weather warnings, tidal current flows, tide times and atmospheric parameters. Users also can access tidal currents, sea temperature maps, wind and wave displays.

Does PredictCurrent also let sailors see ocean temperatures? Yes, in color-coded zones.

Where to learn more: visit www.predictcurrent.com

The post PredictWind Introduces PredictCurrent App appeared first on Cruising World.

Why were we in French Polynesia during cyclone season and an El Niño year? Well, our plan was to sail to New Zealand after six months of cruising in Tahiti, but we fell in love and stayed. So, we ran into cyclone season, which is from November through April in the South Pacific.

The behavior of cyclones changes during El Niño because of differences in sea surface temperatures and atmospheric conditions, influencing the frequency, intensity and paths of the storms. El Niño started in 2023 and continued into 2024, giving the central and eastern parts of the Pacific Ocean warmer sea surface. This can shift the cyclone formation zones eastward. Islands that are typically less affected by cyclones, such as the Southern Cook Islands and French Polynesia, have higher risk.

The Marquesas Islands are outside the typical cyclone belt; their only close call was Tropical Cyclone Nisha-Orama in February 1983. It developed north of the Marquesas during an El Niño year and had sustained winds of 115 mph in the Tuamotus. Areas more frequently affected by cyclones include Australia, New Zealand, Vanuatu, Fiji, Samoa and Tonga—but it is not impossible for cyclones to affect the Marquesas if conditions are right, such as during El Niño years.

Preparation in Tahiti

After a wonderful time diving with humpback whales in Mo’orea, we went to Tahiti to prepare the boat for the journey east to the Marquesas. Wanderlust, our Seawind 1600 catamaran, is equipped with daggerboards. It adeptly sails upwind. This feature, combined with the robust design and comfortable living space, has made it the ideal vessel for us in our long voyages across challenging waters.

In Tahiti, we inspected the rigging and systems, and unfortunately found cracked wires in the cap shrouds and the cross-beam cable (the martingale). The good news was that there are excellent riggers in Tahiti, but the bad news was that the cable had to come from Australia with a lead time of at least two weeks that turned out to be a month. By then, the easterly trade winds would be in full force and on our nose.

Meanwhile, we stocked up at the island’s markets, which are brimming with fresh produce. At every visit, we packed our bags, ensuring our boat was ready to face whatever the ocean had in store.

Papeete Marina

Papeete Marina is on the northwest side of Tahiti, which means it’s open to northern wind and swell. Large waves enter the basin, creating a significant commotion, chafing and breaking dock lines, ripping off docks or surging them over the pilings. In cyclone season, when the northern swells are more frequent, boats are often asked to seek shelter at anchor. As the inclement weather was approaching, we could already feel some of its effects. The monohulls started to behave like bucking broncos.

Finally, our cables for the repair arrived, and Wanderlust was ready.

Strategy

We tossed the lines on December 4 with a plan to sail to Fakarava, setting us up for a good angle to the Marquesas, but the next round of squalls was hot on our tail so we decided to pull into Tikehau, 150 nautical miles to the northwest. The atoll’s sparse population and natural beauty provided a serene backdrop and time to plan the journey ahead. We were held by the weather, but it wasn’t bad at all.

A couple days later, the weather changed, and we had a spectacular sail during the day. Wanderlust chugged miles quicker than expected, and we realized we would arrive in darkness—when it is unsafe to enter the atoll. We furled our screecher and set the jib to slow down a knot or two. A few hours later, the wind disappeared and was replaced by torrential rain. We had to motor and arrived at the atoll’s pass almost two hours after the desired slack tide. Not a real problem with two 80 hp engines, but it could have been with a smaller boat.

Fakarava greeted us with the rare convenience of a fuel dock. However, we did not make use of it, thinking we would be fine with the fuel we had. Rookie mistake. This amenity would have allowed us to bypass the cumbersome process of ferrying fuel in 5-gallon jerry cans, saving time, effort and my rotator cuffs, which I later destroyed in Hiva Oa by shlepping more than three dozen of them.

Fakarava hosts a vibrant underwater world and UNESCO-protected status, with unbelievable diving at the south pass, the famous wall of sharks, and the grouper spawning under a full moon in July. We were fortunate enough to enjoy that during our previous stay. This time around, the squally weather continued, and we did not even take a dip in the water.

Final Leg to Fatu Hiva

With a northwest wind, we sailed close-hauled for three days. Then the wind disappeared, and we motored in flat-calm waters that are unusual for that time of the year. The silver lining was that we were able to land a 143-pound yellowfin tuna that fed us and our friends delicious sushi and tuna tartar for months. And we learned another important lesson: While trying to lift the tuna using the main winch, I may have used the wrong size rope (I admit nothing). The winch stripper arm broke. It was a most expensive tuna, too.

On day four as the sun was starting to set, the southernmost island of the Marquesas, Fatu Hiva, presented its rugged landscape: the perfect gift on Christmas Eve. Giant clouds resting on jagged peaks, the sun’s evening light casting a golden hue on its face. A distant squall reminding us of what we’d been through. We had navigated Wanderlust about 1,000 nautical miles from Tahiti, upwind, to this Jurassic-like sanctuary for cyclone season. In the day’s final light, we anchored in the stunning Bay of Virgins, a spot already marked on the chart plotter from our previous visit.

Fatu Hiva

This land boasts a rich cultural heritage, friendly people and breathtaking landscapes. After spending some time on the island, we found ourselves reverently walking paths surrounded by raw beauty. Eventually, we stopped trying to articulate our awe, and we became part of the larger tapestry of life and nature. Gently running our fingers on the leaves of holy basil to release the magical scent, inhaling the pungent whiffs of drying copra, and bowing over gardenia flowers to take in their exhilarating aroma. Long-tail tropical birds circled above us in the backdrop of lush volcanic peaks.

Kahoha was the greeting we exchanged with the locals. Even Yoda, our dog, became a beloved figure on the island, responding joyously to calls from across the river. We made friends, bartered rope and other items for fruits, and for wild pig and goat meat. We felt a profound connection to this island.

Getting there was worth every bit of effort it took. We lived an unforgettable adventure that brought us closer to each other.

The post Dodging Storms, Chasing Thrills in French Polynesia appeared first on Cruising World.

More than 1 million cruising boaters are now using PredictWind, a weather-­forecasting service created in 2010 by competitive sailor Jon Bilger. He founded the company after serving as weather manager for teams who won the America’s Cup in 2003 and 2007, when he realized that the higher-end technology could be a boon to the cruising public.

“It’s been quite a journey,” Bilger told Cruising World in early March, adding that as the community of cruisers continues to evolve with different styles of boats, PredictWind has been evolving right along with it. Sailors are still the company’s biggest client base, and those who make the shift to powerboats can now also use PredictWind to help with routing that optimizes fuel efficiency. 

That kind of advancement in forecasting ­capabilities is in great part due to ­technology. What’s possible in terms of forecasting today is far different—and much more detailed—than when Bilger founded PredictWind 14 years ago. 

It’s a timespan that might as well be an eon when it comes to technological advancements. When PredictWind was created, the Blackberry still dominated the handheld marketplace. The iPad was brand-new. So was Instagram. Forget about today’s 4K screens; manufacturers were still trying to get people to understand the difference that a 3D screen could make when watching hot new movies like Avatar. Uber was just one year old. Lyft didn’t even exist.  

It was also in 2010 that Google started to personalize users’ search results. Machine learning began to analyze and predict all kinds of things, as wide-ranging as voter behavior and power-grid spikes. As CNN reported: “In 2010, artificial intelligence was more likely to pop up in dystopian science-fiction movies than in everyday life. And it certainly wasn’t something people worried might take over their jobs in the near future.”

Oh, how times have changed—in some ways, for the better. PredictWind is embracing AI to create products that help with weather forecasting in ways that seemed unimaginable until recently. 

Just one example is the company’s newest service, PredictCurrent, which Bilger says is a world first. 

“This is very, very simple,” he explains. “You put your location in. You say, ‘This is the current I want to know about.’ And then, boom, you get a graph. We give you windspeed and wind direction as well, and you get current speed and direction, and we give you a map, so you can actually see, hour by hour, how the current is changing over the whole area. It’s amazing to see that sort of detail on your iPad or your laptop.”

PredictCurrent covers tidal currents for 90 percent of the world’s coastlines, he says. The level of detail and accuracy is best within 90 kilometers (about 55 miles) of the coast, but there is also information about currents as far as 600 kilometers (nearly 375 miles) offshore. 

“It’s amazing. You can see how the eddies and currents are changing,” Bilger says. “Compute power for the whole world is enormous. The storage capacity is there. It’s a pretty cool thing.”

Another new product from PredictWind is called Over the Horizon AIS. Typically, Bilger says, a cruising boater can receive an AIS signal within just a few miles of an oncoming hazard such as a container ship. Over the Horizon AIS compiles data from the Automatic Identification System worldwide—“We pay a lot of money to get that information,” he says—and customizes it for use by individual cruising boats through the PredictWind DataHub smart device.

“This is very, very simple. You put your location in. You say, ‘This is the current I want to know about.’ And then, boom, you get a graph.”

“It can download the data every minute with a Starlink connection, and it shows vessels out to about 300 nautical miles,” Bilger says. “If you have a container ship barreling at you, maybe you have about eight minutes to take evasive action. We can give you something more like eight hours.”

The capabilities that Starlink offers are hugely important for some of these newer features, Bilger says, but he tempers his enthusiasm for the satellite service with a caution for offshore cruisers.

“We genuinely are huge fans of Starlink. It means that people can get weather forecasting offshore, and get it a lot easier,” he says—adding a big but. “If you go offshore, you need to have a satellite phone, an Iridium Go. If the power on your boat goes down, Starlink requires AC power. If you have a problem with your inverter, you have no communications. You really should have something with a battery backup on it.”

With that said, Bilger is gung-ho about all the information cruisers can now access on a regular basis thanks to Starlink, instead of having only occasional access to downloads. The amount of data coursing through PredictWind’s DataHub, coupled with artificial-­intelligence analysis, can create things such as polars for a specific boat. 

These “AI polars,” as Bilger calls them, represent the performance of a boat in different wind and wave conditions—information that can be critical for weather routing.  

“Normally, you select from a predefined list of polars for all the boat types, and then there’s a velocity-prediction program that shows the ideal speed of your boat in perfect conditions,” he says. “But that’s not reality. That’s not how you sail a boat. With the DataHub, it’s reporting your windspeed, your direction, and it averages that data. It sends it back to our service and compares it. Over time, it will learn how you sail the boat, and you’ll even have a different set of polars for daytime and nighttime.”

Today’s level of artificial intelligence is required to make these types of services possible, he adds. 

“Our service is doing billions of calculations for six of the top-level models, and boom, you get the comparison,” he says. “It’s way easier and very powerful to have. You really have no excuse to get caught out in bad weather.” 

Similar use of technology allowed PredictWind to launch a product last year that helps cruisers better understand the wave state that they are likely to encounter. 

“Generally, all weather services give you the primary wave state,” Bilger says. “We have modeled monohulls, catamarans, trimarans, sailboats and powerboats, and every possible wave state. We know exactly how the boat’s going to perform based on length, beam, displacement.”

This level of detail makes it easier for boaters to make better-informed choices, he says. 

“The real kicker is that we can display how much the boat’s going to roll, and whether it’s going to be dangerous to be on deck,” he says. “The other one is vertical acceleration. If you’re going over a big sea state, you’re going to be going up and down a lot, which affects seasickness. And we can talk about slamming. That’s a big one as well. When you do your weather route, you can see all of that during a trip. If you use a departure-planning tool, you can know which day to leave in terms of the degree of roll you’re going to experience. No one else is doing that, as far as we know.”

All of it adds up to more boaters feeling safer and more comfortable out on the water, Bilger says. 

“We get emails from ­families who say, ‘Thank you for keeping us safe all around the world,’” he says. “It’s ­really cool. It’s why we’re here.”

The post The Data Difference: Advances in Marine Weather Forecasting appeared first on Cruising World.

It figures that a hurricane’s projected track aimed right at our Stevens 47, Totem, while we were an ocean away from it, having traveled by jet from Mexico to Europe and South Africa. That was Hurricane Kay, in early September. Last week brought Hurricane Ian, which we watched approach Florida, glued to updates, fearing for the boats and livelihoods of friends along Florida’s west coast.  

Actively tracking weather is one of the most consistent features of life on a cruising boat. You don’t just feel the elements more directly; your immediate security is weather-driven. Looking at GRIBs through PredictWind remains our mainstay weather tool. And, we love the new GMDSS addition: graphical display of GMDSS text forecast details (lows, highs, tropical depressions, fronts) over a GRIB. Anyone in my husband Jamie’s classes at Cruisers University in Annapolis from October 10-16 will see a bunch of these. 

Other specialty tools provide input to keep informed and make decisions about our everyday comfort and safety. Writing recently about chubascos, a weather phenomenon in the Sea of Cortez, we focused on how valuable the GOES band 11 viewer is for anticipating these weather bombs. Here are other tools that may be less commonly tapped, but helpful for those of us living at weather level. 

Weather Radar

Radar is an excellent tool when it’s available. Radar on a boat is a fine way to get squall size, location and tracking to mitigate the conditions (Squall tracking, more than avoiding hazards at the night or in fog, is the #1 use of Totem’s radar, in fact). Weather service radar, accessed via the internet, offers a dynamic wider-region view. This requires internet bandwidth.  

A weather radar source with a time loop helps visualize movement and the squall or front’s increasing or decreasing footprint, to preemptively adjust course and or speed. You may not be able to bypass the weather, but even reducing the duration of your exposure to volatile weather is useful. 

On our last days in South Africa, we actually had more wind than Puerto Peñascohad, Mexico, from Hurricane Kay’s attempted swipe—this front line brought 50-plus knots. It was wild to watch (from inside a cozy beach house), but for locals, was “just another Sunday.” 

Real-Time Lighting

Real-Time lighting strike maps show where the sky is more or less electric. Like radar, this tool provides a visual for a storm’s size, intensity and track. For folks on boats, the devastating power of lightning can be even more daunting than wind and rain. 

We like the display on the website Blitzortung for this, and there are a range of real-time lightning map mobile apps as well.

Satellite Imagery

Another satellite imagery resource is Zoom.earth. It’s instructive, but not targeted. Still, for sharing satellite-informed views of your location without freaking out your kids or in-laws, try giving them this view. The red areas show heat detected by satellites. This tool influenced our driving route to avoid hot-season wildfires.

Surge Estimators

Hurricane Kay ended up tracking outside of Baja, California, a much lower risk to Totem than it might have been if it tracked up the Sea of Cortez. But it was late when we considered that, even though the system was relatively distant, there might be a surge effect near our boat’s location. And, as Murphy’s Law would dictate, of course it would coincide with peak tidal swings in an area notorious for extremes (22 feet isn’t unusual). We watched CERA, a collaboration between the National Oceanic and Atmospheric Administration and Louisiana State University, for modeling surge. It indicated that water might not just rise above the level of the slipway, but also spill further into the yard. Not so good for boats in sand or gravel, and not good news for things on the ground. Like our new-in-the-box engine.

Water level exceeding the slipway would have been a first at the boatyard. (We still, by the way, feel this is the best possible option for hurricane season on the Pacific side of Mexico.) From South Africa, we watched and waited for updates. 

And recently, we watched as the surge forecast from Hurricane Ian developed for Florida—especially Southwest Florida, where folks we care about in Punta Gorda have their catamaran. It was tough to see the surge increase and consider the havoc it caused. NOAA’s estimate was 12 to 18 feet. There’s not much good that comes from an 18-foot surge (or even “just” 12 feet) when you’re tied to a fixed dock. 

Wave And Swell

Boaters tend to focus on the wind forecast, the sea state tends to be a much bigger influence for real feel on a boat. And yet, wave and swell forecasts have long been the least accurate reflection of real feel in the weather toolkit. GRIB Wave forecasts only display one wave forecast at a time. Secondary or tertiary waves and swell, such as a swell from a far-off gale, can really increase the motion of the ocean. The information is often available, but clunky to view and interpret. PredictWind has a new tool set that uses all wave and swell data, and then models roll, pitching and slamming based on specific dimensions of a given boat. Its new Automatic Wave Routing feature is a big step toward interpreting a real-feel to make go or no-go decisions. 

If we’re near a surfing region, we also sometimes use surfer websites such as Magic Seaweed to understand the magnitude of local swells. Farther offshore, there might be a weather buoy near a planned route. Looking at real-time data, such as NOAA’s National Data Buoy Center site, can help determine the accuracy of forecast information.  

Tsunami Danger

This isn’t something we really thought about a lot before cruising, but we’ve ended up needing to track tsunamis a few times when we were potentially in risk zones. It’s no joke, and we know enough people who have had truly dangerous tsunami events while cruising. 

While our first tsunami was a nonevent, the second warranted more attention: We watched as the depth changed 6 feet up then 6 feet down in 15-minute intervals. One boat missed a swing and ran aground in a channel.

What are your tools for this? A U.S. Geological Survey website details earthquakes worldwide, and a global scattering of tsunami monitoring stations are on this UNESCO-funded site.  

The 2022 hurricane season finally did get spicy, as promised. While Hurricane Ian left a trail of heartbreak in Florida, we received news that our friends’ boat in Punta Gorda came through nearly unscathed. So many others did not. Neighboring boats were found sunk, or on top of the dock, or in the adjacent yard. And now, on the Pacific side, we watch Orlene. The tropical depression is expected to become a hurricane, and is tracking toward Mazatlan and the Sea of Cortez, where we lie at the northern tip.

The post Sailing Totem: Adding Tools to the Weather Toolbox appeared first on Cruising World.

Studying weather forecasts is so much a part of the morning ritual on our boat that we automatically associate the smell of coffee with weather bulletins and surface-analysis charts. It doesn’t matter where we are—near a city with speedy Wi-Fi and downloads, anchored in a remote corner of the globe with text bulletins, or underway with the Pactor modem screeching and rumbling for half an hour to get a GRIB file—weather and morning coffee just go together. 

As sailors, we live much closer to the elements than most people. Keeping an eye on forecasts is imperative for the safety of the boat and the well-being of the crew. It’s also a fun and interesting pastime.

Get your bearings. When you start exploring a ­cruising area, the local weather might seem indecipherable. Get a good introduction to the ­dominant systems by ­reading a few articles about the ­regional weather. When is the rainy season? Is there a hurricane season? 

Guidebooks offer a helpful, albeit simplified, overview. For instance, guides to French Polynesia, where we’ve been cruising aboard our 1988 Sparkman & Stephens 41, Pitufa, for the past eight seasons, describe the area as having two distinct seasons: a dry and windy season between May and October, and a cyclone season from November to April with generally rainy, hot weather. This is true for Tahiti and the Society Islands, but the Marquesas are usually dry with two short rainy seasons in spring and fall, while the Gambier and Austral Islands have proper seasons with hot summers and cool winters. If you don’t study this kind of information beforehand, you’ll be in for a few surprises.

Pilot charts. Take a look at pilot charts as well. What’s the strength and direction of the predominant winds? How often do passing low-pressure systems interrupt them? Get an overview, and then choose a few reliable weather sources from the jumble of available information. Check them on a daily basis.

Look at the big picture. When we have a strong internet connection, we download wind forecasts for a large area to observe the distant systems behind the local winds. This technique helps us, for example, keep an eye on passing troughs that interrupt the trade winds, or take note of an acceleration zone on top of a high-pressure system. 

We like to compare the American Global Forecast System model with the one from the European Centre for Medium-Range Weather Forecasts. That way, we can ​see how they differ. We also like to check the models after the fact and keep track of which one was more accurate.

Surface-analysis charts allow us to visually interpret the isobars, and they turn features such as fronts, troughs and lows into comprehensible images.

Some cruisers crop too small of a frame when forecasting and download data on an immediate area without seeing the bigger picture. They’re often flabbergasted (and curse the stupid forecast!) if the wind blows from the opposite direction. By contrast, if you download a larger GRIB file, you might see a convergence zone with northwest winds on one side and southeast winds on the other. The big picture is important to understand because minor inaccuracies in the forecast can result in a major predicament that leaves you pitching and rolling off a lee shore. 

Looking at the big picture also means that you can prepare for multiple scenarios and have alternative anchorages in mind. We like to explore cruising areas thoroughly and have our own GPS tracks to follow to a safe anchorage in the event of a windshift—a tool that is especially helpful if a move must be made during a squall or in the middle of the night.

Get a feel for weather patterns. During a prolonged stay in a protected anchorage, it’s interesting to look at the forecasts every day. What’s typical for the season and area? Do forecasts tend to overestimate or underestimate weather features? How do systems move? What can you expect from windshifts from certain directions—sunny skies or squalls? If you know your weather, then you can enjoy fair-weather sailing downwind or use the windshifts that passing troughs generate to make miles against the prevailing trades. 

Wait for proper windows. Losing your patience and sailing out on a suboptimal weather window is tempting, but it often leads to frustration. Flogging sails in fickle winds, or too much wind from the wrong direction, is worse than waiting. 

Once you find your window, make sure that you have a reliable source for forecasts underway. Whether you’re using an SSB or Iridium, monitoring forecasts means you can change course if needed, or head for an alternative destination. 

Each year, we sail east from Tahiti toward the Tuamotus in September or October, and each year neighbors ask us which island we’re headed for. The answer’s always the same: “Where the wind will allow us to go.” Setting out with winds from the northerly quadrant, we make miles eastward and try to get as far as we can. If the wind shifts back to the east earlier than expected, or has less of a northerly component than hoped for, we have half a dozen atolls from which to choose. 

Keep it up. Continue to look at forecasts even at anchor, and be prepared to move. What looks like a benign calm in the anchorage might, in reality, be an approaching system loaded with squalls. Being prepared with information is better than trying to ride out nasty conditions on the wrong side of an atoll. Fetch can build quickly, and waves can reach surprising heights. We were anchored recently on the east side of Maupihaa in the Society Islands when we noticed that the GRIB files showed a major wind shift within the next two days. Those shifts often come with squally fronts, so we warned our neighbors in the anchorage and set out to explore alternative spots in the atoll that might be safer in the clocking winds. When the front arrived with 30 knots from the northwest, we were comfortably anchored behind a beautiful motu on the northwest side. Unfortunately, the boats that decided to ride out the shift on the east side spent “the worst night of their cruising lives,” according to the skipper of a 50-foot catamaran, even though they were anchored just 2 miles away from us on the other side of the tiny lagoon. 

Birgit Hackl and her partner, Christian Feldbauer, have cruised French Polynesia for eight seasons. For more information, visit their blog.

Check the Charts for Patterns

Cross-referencing pilot charts, local guides, and anchorage guides can offer a good overview and insight into the weather patterns of an area. 

See our satellite data-based global interactive wind atlas at pitufa.at/oceanwinds.

Pacific Weather

The weather in the South Pacific is dominated by two big highs—the Kermadec high and the Easter Island high—with the South Pacific Convergence Zone in between. The trade winds here are not as stable as Atlantic and Caribbean trades, and can be frequently interrupted by troughs that travel along the convergence zone. Every couple of weeks, a passing trough lets the winds clock around, which is annoying when passagemaking westward but handy when hopping eastward along the islands.

We use Meteo France’s weather bulletins and surface ­analysis, NOAA’s surface analysis and cyclone warning site, and the weekly summaries of MetBob’s Bob McDavitt. All of those sites are embedded here: pitufa.at/weather-fp.

For Fiji, see the weather forecasts on the government’s ­official site (met.gov.fj), which includes the marine forecast.

These sources provide a general overview: 

Pacific Crossing Guide (Adlard Coles Nautical); South Pacific Anchorages (Imray); Cruising World, July 2019, “Pacific Weather Routing”; and Cruising World, July 2019, “Pacific Passage Planning”.

We use an SSB radio in combination with a Pactor modem to download forecasts underway, or when in remote areas. SSB propagation is limited to certain times of the day, so some cruisers prefer a satellite phone. No matter which medium you use, saildocs.com provides a great free service to download forecasts, using small files to save data. For French Polynesia, visit pitufa.at/weather-fp.

The post Pilot Charts, GRIB Files and Wind Patterns: Understanding Weather Bulletins, Models and Forecasts Makes for Safer, Happier Cruising. appeared first on Cruising World.

Marine weather guru and well-known seminar lecturer Lee Chesneau passed away Thanksgiving Day, 2021, three years after suffering a major stroke. 

According to an obituary posted on the Dignity Memorial website, after serving in the U.S. Navy, Chesneau spent his career with the National Weather Service, retiring in the late 1990s. He then went on to teach and speak about weather, eventually forming his own consulting business to promote safety at sea. In that role he helped train commercial fishing and recreational mariners on becoming self-reliant on vessel routing and prudent decision making. Together with Capt. Ma-Li Chen from Taipei, Chesneau published Heavy Weather Avoidance and Route Design: Concepts and Applications of 500Mb Charts and numerous other works. He was one of only a few to be certified as an USCG Standard Training, Certification, and Watch Standing instructor for basic and advanced meteorology.

The post Eight Bells for Lee Chesneau appeared first on Cruising World.

NOAA’s Climate Prediction Center is predicting another above-normal Atlantic hurricane season. Forecasters predict a 60% chance of an above-normal season, a 30% chance of a near-normal season, and a 10% chance of a below-normal season. However, experts do not anticipate the historic level of storm activity seen in 2020.

For 2021, a likely range of 13 to 20 named storms (winds of 39 mph or higher), of which 6 to 10 could become hurricanes (winds of 74 mph or higher), including 3 to 5 major hurricanes (category 3, 4 or 5; with winds of 111 mph or higher) is expected. NOAA provides these ranges with a 70% confidence. The Atlantic hurricane season extends from June 1 through November 30.

“Now is the time for communities along the coastline as well as inland to get prepared for the dangers that hurricanes can bring,” said Secretary of Commerce Gina Raimondo. “The experts at NOAA are poised to deliver life-saving early warnings and forecasts to communities, which will also help minimize the economic impacts of storms.”

Last month, NOAA updated the statistics used to determine when hurricane seasons are above-, near-, or below-average relative to the latest climate record. Based on this update an average hurricane season produces 14 named storms, of which 7 become hurricanes, including 3 major hurricanes. Watch this video summary of the Outlook:

El Nino Southern Oscillation (ENSO) conditions are currently in the neutral phase, with the possibility of the return of La Nina later in the hurricane season. “ENSO-neutral and La Nina support the conditions associated with the ongoing high-activity era,” said Matthew Rosencrans, lead seasonal hurricane forecaster at NOAA’s Climate Prediction Center. “Predicted warmer-than-average sea surface temperatures in the tropical Atlantic Ocean and Caribbean Sea, weaker tropical Atlantic trade winds, and an enhanced west African monsoon will likely be factors in this year’s overall activity.” Scientists at NOAA also continue to study how climate change is impacting the strength and frequency of tropical cyclones.

“Although NOAA scientists don’t expect this season to be as busy as last year, it only takes one storm to devastate a community,” said Ben Friedman, acting NOAA administrator. “The forecasters at the National Hurricane Center are well-prepared with significant upgrades to our computer models, emerging observation techniques, and the expertise to deliver the life-saving forecasts that we all depend on during this, and every, hurricane season.”

In an effort to continuously enhance hurricane forecasting, NOAA made several updates to products and services that will improve hurricane forecasting during the 2021 season.

• In March, NOAA upgraded the flagship Global Forecast System (GFS) to improve hurricane genesis forecasting and coupled GFS with a wave model extending ocean wave forecasts from 10 days out to 16 days. Additionally, Global Positioning Satellite Radio Occultation (GPS-RO) data are now included in the GFS model, providing an additional source of observations to strengthen overall model performance.
• Forecasters at the National Hurricane Center are now using an upgraded probabilistic storm surge model — known as P-Surge — which includes improved tropical cyclone wind structure and storm size information that offers better predictability and accuracy. This upgrade extends the lead time of P-Surge forecast guidance from 48 to 60 hours in situations where there is high confidence.
• NOAA’s Atlantic Oceanographic and Meteorological Laboratory will deploy its largest array of air and water uncrewed systems to gather data designed to help improve hurricane intensity forecasts and forecast models. New drones will be launched from NOAA Hurricane Hunter aircraft that will fly into the lower part of hurricanes, and in the ocean, saildrones, hurricane gliders, global drifters, and air-deployable technology — called ALAMO floats — will track various parts of the life cycle of tropical storms.

Last year’s record-breaking season serves as a reminder to all residents in coastal regions or areas prone to inland flooding from rainfall to be prepared for the 2021 hurricane season.

“With hurricane season starting on June 1, now is the time to get ready and advance disaster resilience in our communities,” said FEMA Administrator Deanne Criswell. “Visit Ready.gov and Listo.gov to learn and take the steps to prepare yourself and others in your household. Download the FEMA app to sign-up for a variety of alerts and to access preparedness information. Purchase flood insurance to protect your greatest asset, your home. And, please encourage your neighbors, friends and coworkers to also get ready for the upcoming season.”   

NOAA also issued seasonal hurricane outlooks for the Eastern and Central Pacific basins, and will provide an update to the Atlantic outlook in early August, just prior to the peak of the season.

Visit FEMA’s Ready.gov to be prepared for the start of hurricane season and the National Hurricane Center’s website at hurricanes.gov throughout the season to stay current on watches and warnings.

The post For 2021 NOAA Predicts Another Active Atlantic Hurricane Season appeared first on Cruising World.

Weather always wins. Schedules are the enemy. Between these two principles for safe cruising, Totem and crew have remained in Santa Rosalia for an extended stay – weeks more than anticipated. Our goal destination is only about 250nm to the north: returning to Cabrales Boatyard in Puerto Peñasco to dig into our engine issues. Why is this distance, which we’d normally do in 40 or so hours, proving to be so complicated?

Weather drives our decisions, and it’s the primary reason we are still cemented to the dock. We want easy conditions: partly for our personal comfort, and partly to avoid any situation that could over-work our somewhat compromised engine. We’re a sailboat, so what’s the big deal?

In the wintertime, strong northerly winds dominate the Sea of Cortez. They make slab-faced waves two or three seconds apart. Wind and water from the direction we want to go. We like to live by the code that “misery is optional,” and bashing into square seas for 250 nm is not consistent with that tenet.

These frequent northers generate over the Four Corners in the US southwest and are readily forecasted. But Sea of Cortez weather is also affected by Pacific Ocean weather, complicating the gaps between northers. This diagram helps illustrate: the red boxes are areas between mountain ranges, flatter terrain where gap winds accelerate across to the sea. Those yellow boxes are the dominant ranges, which fuel katabatic (falling) winds.

Our juggle: to find three days of mellow weather that let us get back north. We really need only two days to transit 250 nm, but prefer the extra day to allow seas whipped up by the prior system to flatten. Misery is optional!

This is where our second factor kicks in: TIME. If we are willing to spend a week or more offline, we’d hop one day north to Bahia San Francisquito or Isla Partida in a weather window otherwise too short for the entire trip. We’d wait out 25-knot to 50-knot winds tucked in there, looking for the next window to proceed north. The catch is that waiting period is often about a week.

We are a victim of our success at the moment, unable to take a week off from high-bandwidth internet. Our coaching business is thriving, and frankly, we love it (how lucky are we to be able to help people realize the cruising dream?!), and frankly, we need the income (that engine…).

Supporting between 45 and 50 clients has kept us pretty busy. Almost half of the TRU crew we’re actively working with are recently launched as cruisers, navigating the hurdles of their new lifestyle. Others are more tenured, and it was pretty exciting this week to see our third TRU client close the loop on a three-year circumnavigation. A big congratulations to the Mirabella crew!

While we’re away from cell towers, we keep up with email via our Iridium GO, but our days are filled with video chats to talk about a prospect boat, zooming in to high resolution images of chainplates or GRIB files for weather routing. Adding a number of seminars into the mix means more bandwidth. Text-only connectivity of the GO email is fine for normal cruising, but it isn’t good enough to keep up with those demands.

Are we frustrated or disappointed? No, not really. Sure, we’d really like to be back at Cabrales Boatyard among friends (it’s special! Read our Ode to a Shipyard Community to see why). Santa Rosalia is nice, but there’s no cruiser community to partake in. We miss camaraderie of sharing meals, laughs, and tools with the friends back at Cabrales. Our teens missed another teens birthday, one we were SURE we’d be able to make… by February 28.

In many ways this is a good reminder of some cruising principles that bear repeating. Weather always wins. Schedules are the enemy. In this case, schedules are our inability to be away. That can apply to cruisers who are trying to juggle working while afloat like we are. But it can also apply to those who are trying to get to that next island to meet friends flying in that they’ve invited for a holiday. It’s easy to be tempted into making bad decision that result in being miserable at best, and unsafe at worst, when letting a schedule convince you that it’s OK to tempt the weather.

Meanwhile, we are in early transition away from the northerlies towards what will become light southerly winds, which dominate weather in the relatively airless hot months of summer. And meanwhile, we make the most of where we are.

Marking the one-year anniversary of the pandemic’s arrival in our reality, we look back with the benefit of optimism that there is a better, freer time coming soon. Our daughters turned 16 and 18, milestone birthdays that passed while in isolation instead of being celebrated. They’ve been incredibly patient throughout. Their maturity is a testament to the flexibility bestowed upon them by growing up as cruising kids: change happens, and you adapt. Not all phases are fun, but you make the most of them and carry on to a better time.

Jamie and I wanted to do something special for them. And the happenstance of being parked at this particular corner of Baja, at this particular time of year, suddenly came into focus: directly across the peninsula, the San Ignacio lagoon carves in from the Pacific – and teems with grey whales. For about two months a year, this UNESCO world heritage site is the mating and calving grounds for the migratory whales. And so, we went.

It’s unusual for us to splash out like this. It took a lot of time for me to figure out how we could do this in a way that aligned with our risk tolerance. But with work going well, and money saved from, well, not going out much this year – the splurge wasn’t hard. The ability to book an entire boat to ourselves instead of sharing it with folks who may not share our risk profile made it possible.

Can you imagine the feeling of being checked out by a whale? We first experienced it in Papua New Guinea when false killer whales made flyby passes, rocketing by our dinghy. The Greys were entirely different: the massive mother parking herself immediately below, and perpendicular to our panga. Her curious calf first spyhopping, then riding up on her back to get a closer look at the above-water creatures.

We’ve seen a lot of badly done whale watching, with aggressive guides bent on delivering “the experience” to the benefit of tips and the detriment of whales. This bore no resemblance, and our captain’s respect for the whales and other boats in the area unquestionable. Despite 27 years’ experience driving boats in the lagoon, his unjaded enthusiasm greeting the whales that approached our small vessel was the best and only kind of contagion we encountered.

It’s a bright spot, one among many which feel like they are gathering to move us all forward, slowly, surely!

The post Sailing Totem: Weather and Schedules, the Laws of Cruising appeared first on Cruising World.

—Behan

On this day, I have two boats galloping north at 10 knots. The sailing is nice, boosted by 3 knots of Gulf Stream current along Florida’s east coast. This has elements of a unicorn passage. After dark, it’ll be all dragons. I’m anxious for both families. I didn’t exactly send them out into this night. But I didn’t stop them either. Realtime weather radar shows heavier rain approaching. Florida now has tornado and flood warnings. Damn. Lightning hotspots continue to increase along the coastline. The dragons are coming. 1,700 miles west, Totem bobs in softening afternoon wind waves in the Sea of Cortez. We haven’t had a drop of rain in 6 months. No dragons either. We’ll have a gorgeous full moon rising over Isla Carmen in a few hours. Nothing like my Gulf Stream boats speeding through darkness and dragon fire. I am the chess master, sliding pieces past danger. I am the fool, thinking I control the board.

I’ve only recently come to accept that I provide a weather routing service. I’m not a meteorologist, not even a pretend one. I’m never the assertive voice when a group of sailors debate a weather window for the next passage. Information sharing is helpful. Selling an interpretation only masks a hidden agenda. I thought I understood weather forecasting pretty well when I was a racing sailor. Weather had tactical value and I was competitive. Then came the first big and very unexpected squall while delivering a J/35 to Newport, RI. Didn’t see that coming, but could have if I’d known where to look.

Family cruising in Puget Sound and beyond shifted desired weather traits from tactical to comfortable. The unicorn passage: fully at ease with surroundings in the magic and enchantment of glorious sailing. Unicorns are rare, elusive. Waiting is tedious; not getting you to that next beautiful anchorage you’ve dreamt of, frustrating. Instead, interpret the forecast and go. Rarely expecting unicorns, always hoping not to see dragons. Sometimes getting it right. Sometimes not, always comparing and contrasting forecast and reality after the anchor dropped. After hundreds of passages and assessments, my technical weather knowledge is hopelessly mediocre. My particular weather superpower is translating meteorological data into “this is what it’s going to be like.”

My Gulf Stream boats aren’t off to the next dreamy anchorage. They’re retreating to neutral territory. Like many, they’d been COVID-19 restricted in the Caribbean. Uncertainty of a global pandemic and hurricane season looming like a nightmare monster set them on a path to Maine. It’s a return to home for one family. A gorgeous new cruising region for the other. A big step closer to predictability for both. The path is about 2,500 NM long. Beginning in turquoise water of the US Virgin Islands, where warming temperatures bring increasingly volatile weather. Going north in May and June quickly bumps into colder weather and frequent gales springing from the East Coast out into the cold Atlantic.

A few weeks before picking a good enough window to depart paradise, we began the conversation of which route home. We sailed Totem from the Caribbean to New England in 2016, on a direct route via Bermuda. This shaved 1,000 NM from a path along the US coast. Due to COVID-19, Bermuda was now closed, and the likelihood of gales was high, so, no go. A less offshore route meant skirting the Bahamas, but they were also closed—even for vessels in transit. This longer path without bailout options suddenly got riskier. Fortunately, Salty Dawg Rally organizers stepped in to help. They worked with Bahamian officials to create an innocent passage status list of boats for cruisers repatriating the US and Canada. Once on this list, crews could stop in Bahamas to wait out weather, or procure food and fuel.

With a bailout in Bahamas possible, most of the dozen boats that sought out professional weather guidance from this amateur router preferred to skirt east of Bahamas and make landfall in Chesapeake Bay. This unlikely outcome wasn’t realized by any of them. Through the weather window, I could point out dragons lurking. Boats began peeling off to take innocent passage through the Bahamas. Better to make some progress than wait and wait for the unicorn passage. These boats leap frogged through the Bahamas, unable to step ashore but grateful for the respite. Each made landfall in Florida.

My last two boats, patient or stubborn I won’t say. As their weather router, it’s not my role to tell them when or where to go. It has to be their choice. It can be frustrating, when they don’t follow what I think they should do. Then I remember the times I chose poorly. This includes last night on Totem. I thought the afternoon swell would fade for a flat night and easy sleeping. Instead it was a restless, rolly night at anchor. There is no crystal ball. I don’t push my interpretation, only describe what I see.

A huge low off of New England, with a trough extending to the Bahamas, blah, blah, blah. I picture myself with the young families. One with some offshore experience. The other hadn’t sailed overnight before. I picture the headlines: Virgin family departs Virgin Islands for innocent passage to Bahamas. What could go wrong…? Both boats added experienced crew. With a gift of easier whether, they managed nicely. Weather got more complicated as they went, but they arrived in Florida without drama.

On this night, northbound along the Florida coast, finesse is the key. I described volatile conditions before they set off. No bad wind or waves, but potential squalls to 40 knots, and lightning. Those dragons are real and can be terrifying. A quick start guide to successful family cruising would do well starting with this rule #1: Avoid Terrifying.

My guidance was for a slow start to let the band of unsettled weather pass ahead. I watched the satisfying progress on their satellite tracker positions. They were only 50 miles offshore, within real-time weather radar range. With another online resource I could track real-time lightning strikes. On another browser tab I rechecked the GRIB Rain forecast for the 20th time. Lifeless gray blobs, with smaller pink ones denoting rain intensity. Lifeless, almost meaningless until you see the dull blobs as the smoke and flames from dragon fire. That gets the heart rate up.

The tools I used aren’t meant for piloting, but that’s how I used them. To navigate around hazards. Crudely plotting the lightning’s advance (radar and lightning screens didn’t show lat/long lines) I went against my own rule not to tell them what to do. “Speed now please, all you can make. And change course ten degrees to starboard,” I typed into the message box. The screen confirmed the message sent. Several minutes passed before the reply arrived, “Headsail out, sails trimmed, and course changed. Making out lightning in the distance.”

Virtual chess and mythical creatures. I could feel their tension as lightning approached. Almost hear the voice crack, if there was a voice in the next message, “lighting is getting intense, will we miss it?” With a few more course adjustments, volatile weather passed just south of the two boats. Actual conditions reflected forecast conditions pretty well, except for being 40 miles closer to my boats then the lifeless gray blobs showed. I learned a long time ago that the weather isn’t supposed to do what the forecast says. The dragon that was supposed to strike fear deeper into the night, was now gorgeous lightning safely astern. Another experience. Another assessment. Another way to express lifeless gray blobs.

The post Sailing Totem: Unicorns and Dragons—Confessions of an Amateur Weather Router appeared first on Cruising World.

What cruiser hasn’t blamed a meteorologist for a bad forecast when caught “unexpectedly” in a boisterous blow? “It was only supposed to be 15 knots, but that forecaster couldn’t get it right if Mother Nature shouted the answer.” 

Supposed to be—as if a forecast were instructions for atmosphere and ocean to follow. I have a whimsical theory, in fact: Impugned for ruined weddings and rough days on the water, clever and dedicated meteorologists created computer-derived weather forecasts packed into a digital file called a gridded binary, or GRIB file. These GRIB forecasts deflect hurtful sentiments away from sensitive scientists and onto emotionless computers—and that’s how meteorologists get the last laugh: The various computer models require an understanding of how the data should be interpreted. In other words, a faulty forecast might be user error after all. 

Picture, if you will, weather geeks in a breakroom, pocket protectors and all: 

Wx Geek 1: “So this saltier- than-thou type returned to the marina complaining about the GRIB forecast—it was only supposed to be 15 knots he said.”

Wx Geek 2: “Let me guess, he thought that meant maximum wind speed?”

Wx Geek 1: “Better still, he never checked the gust forecast that showed 30 knots!”

Cruising our Stevens 47, Totem, through Papua New Guinea was a stark reminder that we take weather tools for granted. On Panapompom Island, children gawked at us, the strange visitors, and squalls seemed always on the horizon as we walked the beach talking to islanders. Tumbling in the surf was the carved bow section torn from a canoe. Lateen-rigged outrigger canoes are the primary mode of transportation throughout Papuan islands. One woman matter-of-factly said, “Sometimes they don’t return.” 

Conditions in the region were tough due to a stalled low-pressure system. We expected it well before heavy grayscale clouds arrived, thanks to a GRIB forecast downloaded with our SSB and Pactor modem. Papuan sailors are skilled and tough as nails, but the destroyed canoe in the surf exposed the consequences of a thousand-year technological gap between us. 

Safety at sea is immeasurably better because of weather forecasting. Weather predictions are imperfect, but here’s the catch: GRIB forecasts are a series of images with symbolic meaning; the forecast is how you interpret those images. Put another way, you are the forecaster.

Van Gogh’s “Starry Night” has nothing to do with weather forecasting, but the celestial whorls share more than passing resemblance to the swirling flows in a GRIB image. My untrained interpretation of “Starry Night” is thin: captivating colors that seem alive with movement. That’s all I’ve got. Professional interpretations online speak of turbulence, agitation, a cypress tree representing a bridge between life and death. It’s easy to have an interpretation of GRIB images, but is it the whole meaning? Or do you need to dig deeper?

A GRIB Is Not an App!

There are a number of meteorological agencies worldwide that create global and regional GRIB forecasts. Agencies within the National Ocean and Atmospheric Administration and the European Center for Medium-Range Weather Forecasting are the biggest GRIB sources. Each produces multiple forecasts, called GRIB models. For example, a few of the GRIB models created by NOAA agencies include: 

• Global Forecast System, depicting surface wind, ­pressure, precipitation, etc.
• Real Time Ocean Forecast System, displaying ocean currents.
• Wave Watch 3, predicting waves and swells.

In addition to national sources, private companies produce GRIBs, such as PredictWind’s PWE and PWG models. On the whole, it’s a dizzying display of acronyms! The takeaway is knowing that GRIB sources and GRIB models are different than the app or viewing tool.

Windy, Passage Weather, Ventusky and many other apps/viewers don’t create a GRIB forecast, they only display it. An app is like a theater, and the GRIB model is the film being shown.

GRIB viewers are set apart based on which models they offer and what control features are available. Maybe they show only one model, or don’t reveal important information about the GRIB. Or perhaps they don’t have the option to limit file sizes for offshore or remote downloads using a satellite device or Pactor Modem.

When choosing and analyzing GRIB files, here are technical criteria to consider:

Geographic area: The bigger the forecast area, the bigger the file size. If bandwidth is constrained, it’s best to use a GRIB viewer that enables a user-defined area to manage download size. How much area do you need? Your planned route is the obvious starting point, but sometimes a broader area can show weather systems that will affect you later.

In 2016, we sailed 9,614 nautical miles from South Africa to the US. Between Bermuda and Connecticut, a maze of current eddies, meanders and filaments splintered away from the Gulf Stream to make it one of our least comfortable passages. We used GRIB current forecasts to minimize foul eddies and wind against current situations, but water flow was too dynamic. Had I not been so miserly and insistent on small area, small file size, I might have seen current flow patterns to pick a cleaner, more comfortable path.

Resolution: Often overlooked, GRIB resolution is a major reason that cruisers get the forecast wrong. The color shading on GRIBs applied by some viewers is used to represent wind speed, wave height, etc. At first glance, it appears as though a supercomputer calculated forecast data for every pixel on the screen. But it hasn’t. Resolution refers to the spacing between the actual calculated data points. Wind-barb symbols, when shown, reveal the real spacing. All spaces between them are shaded by the viewer, which is making its best guess at what the wind speed will be. At the source, GFS model resolution is 18 miles (28 kilometers) and ECMWF models can be 5.6 miles (9 kilometers) or 11.2 miles (18 kilometers), depending on the model. For perspective, 18 miles’ resolution means that one data point represents 324 square miles. One data point per 5.6-mile spacing covers 31 square miles. High resolution means less estimated information but creates a problem for sailors. The GRIB file size quickly becomes too large to download offshore or in remote areas using an SSB radio or budget satellite communications. Fortunately, GRIB resolution can be dialed back. A medium resolution of 31 miles (50 kilometers) has one data point per 961 square miles; low-resolution spacing, with data points 62 miles apart (100 kilometers) has one data point per a whopping 3,844 square miles! If there aren’t features in a 3,844-square-mile area affecting your weather, then that might be all you need. Add land, though, and the low-resolution forecast won’t show wind deflected, blocked or funneled—or seriously altered as land heats and cools on a daily cycle. Along a coastline, the gap between data points that span land and sea, and estimated wind speeds displayed by a viewer’s color shading, can be seriously flawed with low resolution. The overland prediction often has little resemblance to wind over water. With big spacing, the viewer’s color shading could, for example, show 30 knots of wind 30 miles offshore and 10 knots nearshore because the overland data points skew the speed estimates in between data points. In reality, those 30 knots could carry to just off the coast, causing problems for a coastal sailor. Always know GRIB resolution, and use high resolution when you have the bandwidth on board. When you don’t, remember that land has a big impact on any forecast.

Duration: The number of days covered by the forecast is known as duration. It can range from one to 16 days. Forecast accuracy tends to be high for the first three days, then decline with each successive day. What value does a 16-day forecast have if only the first three are accurate? It can show trends. 

Let’s say you’re in the British Virgin Islands and want to make the 170-mile trip to Antigua. This is against prevailing easterly trade winds and can be a slog. Looking at longer-duration forecasts reveals trends that help find a better window for the passage. Trade winds blow with consistency but still cycle up and down, and occasionally break down completely. Using a large-area and long-­duration GRIB forecast, tracking weather across the broader area can hint at local conditions days later. For instance, maybe a gale flowing east from the Carolinas will have enough impact to shut down the trade winds for a smoother ride across the Anegada Passage.

Increment: A GRIB forecast is a series of snapshots; increment refers to the number of hours between those snapshots. Options are three, six, 12 or 24 hours. Smaller increments help to show changes more clearly over small areas. Larger increments have the benefit of smaller file size while being adequate to look at trends over a large area. 

Work with the Elements

The features that define the forecast are its elements. Wind is the most common used by sailors. It’s a start, but taken at face value, is misleading. Taken without considering other elements underutilizes the full value of GRIB files. Here are tips to get the most out of a GRIB forecast:

Pressure: Differences in pressure make wind. To see this, look at the black lines on a GRIB indicating ­pressure changes. As the gradient spacing gets closer, the wind ­increases. Use pressure to better see the big-picture weather.

Wind: How much does the forecast really indicate? Forecasted wind speed tends to be interpreted by sailors as representing the maximum expected, but in fact, is an average of the top range expected. A blustery spring day showing 20 knots can have wind ranging meaningfully higher and still fit the forecast. Also note that wind forecasts struggle for accuracy in whisper-light conditions. 

Gust: Short bursts of higher wind speed can be much different than the wind forecast. Ignoring the gust forecast is disregarding an excellent indicator of what the highest winds might be. Comparing wind and gust forecasts is a gauge of volatility: the larger the difference between them, the less stable conditions are.

Waves: Sea state affects comfort on board more than wind. Unfortunately, sea-state forecasts require the most experience to conjure an interpretation. Wave forecasts predict height, direction and period. Height is not the maximum size but rather the average significant height. Waves forecast to be 6 feet can have a 1-in-1,000 wave that is 10 feet. 

Forecasts don’t quite ­capture the “real-feel” out there. Prediction algorithms don’t account for local factors such as coastal topography and bottom contours that amplify size, compress period, or make sea state erratic and confused. Multidirection sea states are common offshore but don’t make GRIB forecasts either. To better interpret wave forecasts, consider the things that push and shove water out of pattern. 

Current: Along the coast, tide charts are useful for routing with a speed advantage. Ocean currents are often forgotten about, their forecasts underutilized. Ocean currents are often irregular and shifty, but they are worth identifying to route for efficiency and avoid uncomfortable sea states created by conflicting flows of wind and current. 

Rain: A GRIB rain forecast indicates if it’s time to dust off the foul-weather gear. It has more value as a gauge of volatility. Rain is indicated by inches or millimeters per hour. High rainfall tends to be part of volatile weather conditions.

CAPE: This is an acronym for convective available potential energy. It’s a measure of atmospheric instability, such as thunderstorms and squalls. A high CAPE index doesn’t guarantee their formation but indicates their intensity.  

Cloud: A GRIB cloud forecast is a good indicator of visibility when sailing at night with little moonlight. It also might highlight an area of volatile weather such as a frontal system or trough. 

Indexing: Using a single GRIB model might show the best forecast available. It also might show the worst. Looking at multiple GRIB models sets up a problem: When they differ, how do you know which has the better prediction? I’ve listened in on some group-think weather ­discussions where a participant pushed a particular forecast. Turns out that this GRIB best fit their schedule, so they wanted it to be true. That’s gambling. A better method to follow is what I call indexing the models. 

The idea is simple. Study the GRIB models you have available. When they all agree on conditions, the real weather is likely to be as forecast. When they don’t agree, watch the real weather and make a note of which models trend closest to reality. A pattern will emerge. If you sail to a different region or slide into a different season, then re-index because the most accurate model might change. There might not be a single winner, but one model might be better for wind and gusts, and another for the rain or CAPE. When we crossed the Indian Ocean, PredictWind’s PWE was best by far for wind, GFS was best for rain and CAPE forecasts, and ECMWF was the best read of sea state. It took a little more work to download and view them all, but it made for a sweet trip across a lively ocean.

Just as it’s important to start with multiple GRIB models, it’s best to use multiple forecast resources when facing challenging passages. GRIBs give us convenient information anytime or anywhere, but always remember that you are the forecaster. If that makes you uncomfortable, consider the aid of a professional meteorologist to interpret the data for you. Hiring a weather router is a smart way to start cruising with better weather information, while learning in the process. Just don’t complain when results are imperfect! It’s a tall order to predict the future.

Jamie Gifford is a sailmaker, and along with his wife, Behan, provides coaching to fledgling cruisers. The Giffords have completed one eight-year circumnavigation aboard their Stevens 47 Totem, and are about to set off across the Pacific again. You can follow their travels at cruisngworld.com/sailing-totem.

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