Weather Windows and Crossing the Gulf Stream

Getting to the Bahamas requires crossing the Gulf Stream. For most people, the task is either intimidating or completely routine. The difference comes from understanding conditions one’s likely to encounter in the stream. The stream can be a raging hell cat or a docile kitty. Since we crossed the gulf stream and seem to be getting around the Bahamas ok, we figured we should share some of what we have learned.

DSCF6575 - Version 2Conventional wisdom on crossing the stream is to get across as quickly as possible and avoid crossing when the winds have a Northerly component to them.  The idea here is that since the Gulf Stream (or more correctly Florida Current) flows towards the North, any wind from the North opposing the current creates a nasty, potentially boat eating, chop.

Before we crossed the Gulf Stream, Lisa and I did a bunch of research on how to find that magical weather window to get a smooth ride over. Unfortunately, we didn’t find much detail on the exactly how to pick a day. Fortunately, we have a great resource in Vanessa, a friend of ours in Key West. Vanessa pointed out a several things that we needed to factor in before making a decision — the most important being current.

Rule #1: Know the current and avoid opposing winds

Vanessa’s guidance was to avoid situations where the wind and current are opposed. This applies to the Gulf Stream as well as other areas like the North West Channel and Tongue of the Ocean in the Bahamas, and pretty much anywhere else like the West Coast of the US where you can find strongly opposed wind and current.

With crossing the Gulf Stream, this is a little trickier than just picking a south wind. The gulf stream has eddies that spin off periodically. If you catch one of these eddies, it’s entirely possible to have most of your ride be smooth and then get beaten up in the end when you hit an eddy with an opposing south wind.

Rule #2: Look for a wave interval in seconds that’s greater than 1.6x the wave height in feet.

What makes life uncomfortable isn’t wave height per se, but how steep they are. For example, three foot waves aren’t a problem. Three foot waves on a two second interval will make Pearl buck like a bronco. I was given this rule of thumb by a fisherman on the Oregon coast when I was contemplating crossing the Columbia Bar.

In general we look for a wave period that more than 2x the wave height and have been quite comfortable so far. The math is easier with 2x.

Rule #3: Use your OWN judgement

Regardless of what the weather gurus, services, and anyone else says, use you own judgement and interpret the data yourself. It’s your boat. It’s your life.

Everyone has a different comfort level. Chris, a good friend of ours, enjoys surfing his boat down large waves, a bottle of rum and cutlass in one hand, the wheel in his other, and a cigar stuck between his teeth. No offense to Chris, but he’s been sailing most of his life and has a very different skill and comfort level to Lisa and myself. That’s something he can do safely.

Chatting over drinks with various people, we’ve heard lots of tales of regret where someone decided to join a group of other boats and had a miserable time or a dangerous ride. Lisa and I prefer to use our own judgement even if it means we travel by ourselves. We take our time and pull back whenever we are not comfortable.

As a result, Lisa and I tend to pull data from a number of different sources before we make a GO / NO GO decision. What we like to see is a consensus between all the data sources. There appear to be at least two different weather models that services use that can offer quite different forecasts — hence our interest in consensus.

1. Hybrid Coordinate Ocean Model (HYCOM)

Hycom offiers insights into what gulf stream currents are doing — particularly eddies. If you would like to find out more about HyCOM, you can browse their website. What’s more interesting, however, are the forecast models for the speed and currents layers for the Florida Keys and the Gulf of Mexico that are found here.

There are two links to check out. One is an animated forecast for the speed and currents layer for the next 30 days. The animation gives you a good sense for what’s going on but it zips by pretty quickly. You can step through the individual images here. Make sure you read the information at the top of the page to figure out what to look at.

While this isn’t the most user friendly site, it does give you access to raw information that other sites synthesize.

2. BuoyWeather

We like Buoyweather for several reasons. The most important being that you can create virtual “buoys” along a route that you are planning save them as favorites, and either get automated daily emails or send an email to query their servers for that predefined location. You can also get passage forecasts that are optimized for low bandwidth connections. The site contains a lot of information, you just have to play with it for a bit to get it dialed in to suit your need. While you can get decent information off the free version of the site some of the most useful features require a subscription.

Note: for some reason, access to buoyweather in the Bahamas is quite slow.

3. AviationWeather

This is an aviation rather than sailing related website. It does, however, offer great insight into the “big picture,” where the highs, lows and fronts are and how they are moving. The key here is understanding what fronts are going over you. I like looking at the surface prognostication charts for this.

Typically in Florida and the Bahamas, as a front approaches the wind shifts to the north. As is passes, the wind clocks around to the east, south, and west before returning to the prevailing pattern for the season. Looking at the speed at which the fronts travel will give you a sense for the intensity of the weather you may encounter.

4. NOAA Weather

No weather evaluation would be complete without a look at what NOAA has to offer. It’s pretty easy to get lost on their site. I like to check the Marine Forecasts and the Hurricane Forecasts at the very least.

Another feature this site offers is the ability to get text-based information via email (ftp-email gateway). This is super helpful on low bandwith connections like packet radio links. There is a lot of information you can get using this method. It is intended for geeks and is NOT user friendly.

5. PredictWind

We use predict wind as well as Bouyweather. While I like the wind forecast wind and swell forecast graphics, I find the service a bit annoying. I feel like they try to upsell you on higher levels of service by versioning their product in annoying ways.

 

We’ve found out that if we stick to the rules listed above and check our weather information sources, we can have a nice time sailing. Eventually, we will get caught by something unexpected — like a squall with 65kt winds while we were at anchor. That for us, however, is a part of the magic of cruising.

We hope you’ve found this post interesting and/or useful. We’d love to hear from you if you have alternate services, rules, and/or tips and tricks that you use to avoid weather.

 

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