It’s not how fast you go… It’s when you leave… Modern Weather Routing and Departure Planning

Modern Weather Routing and Departure Planning

Thursday, December 14th
Althea is currently tucked up in Great Lameshur Bay in St. John USVI. Cara and I sailed here from Francis Bay Monday morning, around the east side of St. John and a little less than half way down the S. side in 18-24 knots and pretty big seas. A full reef and a reefed down staysail were warranted. It was sporty, but not as sporty as the cold front that ripped through Narragansett Bay early Monday morning! Saw the reports at the anemometers around SNE at 35-45 knots and some gusts on the Cape at 50+. That’s plenty breezy!  We have decided to hunker down here for a few days with the impending 30-35 ENE breeze and large Northerly swell forcasted for Tuesday through Thursday morning. Not a bad place to be “stuck”!

(Current situation!!)

The Weather Geek

I am known in the Sail Newport office as the resident weather geek. A badge of honor that I wear proudly! I can’t help it. I love watching weather, I respect weather, I like to know what is coming and more importantly, why it is coming. I do this for safety of our sailing programs where wind and severe weather forecasts are super important during our sailing season.

At Sail Newport, we use several tools (see favorite apps and websites below) including wind, radar, long and short range prediction apps and websites as well as a good dose of local knowledge of Narragansett Bay weather trends to understand what’s coming down the pike. One of my most important and most often used tools is PredictWind. Their powerful forecasting tools (both web based and app) offer the best in graphical wind, wave and severe weather (CAPE) weather predictions. They have all the top global and regional weather models and have recently integrated the high resolution NAM and HRRR models which are updated several times a day. PredictWind has really changed the way that sailors can forecast weather in their area. We have the “Professional” subscription level this and it has been an important tool for us.

Departure Planning and Weather Routing:
To say that weather and offshore wave prediction programs and navigational tools have come along way is an understatement. Comparing the techniques for offshore departure planning available in 2024 to those available in the middle of the last century is like comparing the current editions of smart phones to carrier pigeons.

Just in the last 3-5 years, offshore departure planning has taken a giant leap forward in terms of safer and smoother passage making. One of the tools passagemakers have is the PredictWind departure planning app. This can be used prior to departure for planning and en-route when used in conjunction with their “DataHub”, “oOffshore App” and a good satellite internet link for onboard routing. It is easily integrated with other elements of your ship’s instrument like your onboard sailing instruments or routing software on your PC.  They have recently enhanced this feature through predictions of wave models and utilizing your boat type and dimensions to forecast sea conditions on your trip.

Nick Olson, Marketing and Business Development Manager explains a bit more: 

“For me, the most significant improvement with this tool has been the inclusion of wave modeling for each vessel. In both departure planning and weather routing, we can now use the vessel’s dimensions to create a 3D model and calculate roll, vertical acceleration, and boat slamming. To do this, we consider the wind wave, primary, secondary, and tertiary swells for every route. This information is then displayed in the departure planning/ weather routing tables, making it easy to compare a rough passage versus a smooth one based on your chosen departure time. The best part is that this can be done for a 30-nautical mile passage with hourly departure steps or a 3000-nautical mile passage with daily departure steps.”

PredictWind Routing and Departure planning:
Figuring out a “weather window” for a 600 plus mile trip is crucial for safe (read comfortable!) passages and we have used PredictWind exclusively for picking our departure dates for our two long passages. This tool can be used for shorter passages. We have used it to avoid thunderstorms in SNE and today, we used it to time our departure (0815) to miss the 28-32 knots forecasted for early afternoon.

During the planning of these long hops, I used this app to find a 4-5 day window with:
• Moderate wind, sea state and beneficial wind direction for safe passage making
• Limited opportunities for “severe weather” ie Thunder/lightning/frontal passages
• Be more of a reaching wind direction to avoid an upwind slog or dead downwind
• Manage the time motoring due to fuel constraints of Althea

Polars are important.
The PW developers have created a tool that allows for the user to input their boat “polars” so as to be able to predict the best route to a destination based on predicted weather models. The app takes your predicted boat speed at various wind angles and creates a route based on those predicted boatspeeds and wind angles. They have also added scores of popular designs, so if you don’t have accurate polars of your own, you can find a boat similar to yours as a starting point. There is even a function where you can set the parameters to say you will motor at “X” speed if your sailing speed is under “Y”. That will help you identify how many hours you will be motoring on your passage. We use “Motoring at 7 knots” if “Sailing Speed is under 6.1” as our motoring setting

To use the departure planning tool:
• Load your polars and then choose your first possible departure time and date.
• Then choose what time increment you want the program to use for potential departures. You can choose 6,12,24,36 or any other hourly increment to determine your options for leaving.
• When you hit submit on the app you will get a series of routes using the different weather models graphically on the chart and even more importantly detailed or summary tables of what to expect over the duration of your voyage.

Here is a routing for a trip to Bermuda with a departure every 24 hours starting December 11th at 1400 EST. (looks like #3 is the best to me!!  Waves better, no beating to speak of, less motoring and moderate waves.) 

For our Newport to Bermuda run I was running departure planning routes for about a month to practice using it as well as identifying weather trends in the North Atlantic. Southern New England was getting pounded almost every weekend from early September through October with low pressure systems. Like clockwork, every 5-8 days a low-pressure system forming off of the SE coast of the US or a near miss by a tropical disturbance ripped over the waters between Newport and Bermuda. We needed a break from those systems to get us a window to leave in later October! The departure app had a lot of warning messages each and every time I tried to find a 4-5 day window.

Finally it was a hurricane that was meandering off of Bermuda (Tammy) that finally helped clear things out to (theoretically) get us a 4-5 day window of good weather with SW-W breezes and under 3 metre seas. By the 22nd of October, the PredictWind app highlighted Tammy moving East, away from Bermuda. A window to depart over the weekend of the 28-30th was opening. As time went on through the week of the 22-28th, all models started matching up to provide us a good window with a morning departure on Oct. 28th. With any of these apps, you REALLY need to use them in conjunction with experts. We reached out to our friends that do a ton of offshore sailing and also contracted with Commander’s Weather Service to reinforce what we were seeing.  (They were fantastic!)

So, we went for it! As you have seen in our prior blog posts, all was perfectly aligned and we had wonderful conditions for departure and for 3+ days into the leg to Bermuda! We were initially expecting headwinds of 12-17 for the last 8 hours or so, but the forecast (and reality) was really good for the most part.

But… as you have likely read in the prior blog post, 36 hours into our trip, as we were motor sailing through the gulfstream in the well predicted 6-8 knots of westerly breeze and a bright blue sky, the new downloaded weather models showed a previously un-forcasted low that decided to develop along a frontal boundry near Bermuda JUST as we would be approaching Bermuda from the north and west. This low would intensify over the 31st and by the 1st, be a full gale.  (Link to Bermuda Trip Post for that story)

Communication en route.
Modern satellite communication is incredibly helpful for updating forecasts from the big 3 weather models which include the GFS, Euro (ECMWF) and the UKMO. We have 2 communication platforms. Primarily, Starlink (the new maritime dish) which is faster than our home cable internet. It is $2500 for the dish and $250 per month for 50 gig. We invested in Starlink as well as a used iridium go which is used as a backup satellite link. Using the Starlink, we were able to update our routing on PW when the models were updated (early to mid afternoon and early AM). Using the offshore app and the DataHub from PW, our polars were constantly updated when we were sailing and we could run routes that were hyper accurate. The DataHub provides tracking information so folks can follow along and see our speed and the wind strength and direction along our route. (https://forecast.predictwind.com/tracking/display/SY_ALTHEA/)

For our offshore passages, we also combined the power of the Starlink and PredictWind App with one of the world’s top navigational software programs called “Expedition” that we use on the laptop. Expedition allows us full navigational charts (C-Map) which link to the boat’s B&G instrumentation, AIS and even Radar. We use the polars from our PW account and GRIB files downloaded either from the PW site or use “LuckGrib” which is a mac or pc based app for downloading weather, current and wave files onto your laptop. I have used Expedition often on offshore races in the last dozen or so years and most recently on the doublehanded racing I have done with Kenny.

The Starlink also allowed us to ask questions to our onshore weather service. We sent emails to them as soon as we saw the potential for the low developing in 2 days time. They confirmed what we saw on PW and concurred that we should get as far east as we could in anticipation of the pre-frontal SE breeze…. (Reminder, we saw this possibility 2.5 days out which was crucial. If we hadn’t known, we would not have pushed hard and would have been in 30-40 knots on the nose with 12-15’ seas.)

Nick Olson provides the last word:

“Our goal is to provide more than just wind information for the route. We strive to include additional details that aid seamanship, such as ocean current and wave modeling outputs to see how your boat will react to the sea state, AIS to prepare for busy areas or avoid fishing fleets, and extreme weather warnings along the route. Additionally, we have GMDSS forecasts displayed in graphic form, where we use AI machine learning to read all GMDSS forecasts and convert them into images. That way, we can provide our customers with as much information as possible in a simple and digestible manner, helping them make better decisions when it comes to weather.”  (please stay tuned for full interview with Nick in future blog post) 

These modern applications, used in conjunction with expert analysis is the biggest safety improvement in a cruiser’s bag of tricks. As the self-proclaimed weather geek, I love this stuff.

Brad Read

Althea’s Weather/Navigational apps and Computer models:
• eWeather: Just a wonderful weather app for the SE New England area! No hype, great information and especially good with tropical systems and frontal passages in the summer and snowfall prediction and severe weather in the winter.
• Radar US+ (US only)
• PredictWind
• Sailflow/iWindsurf/ iKitesurf
• Expedition 4D
• LuckGrib
• https://ocean.weather.gov/Atl_tab.php