HOW ACCURATE ARE MARINE WEATHER FORECASTS?
Modern technology has made boating easier and more approachable over the past few decades. Gone are the days when you had to learn how to use a sextant and needed to rely on the barometer for a very approximate marine weather forecast.
Nowadays you can check an app on your smartphone to find out what the wind speed, swell, visibility, and tide are. You can even look at a weather radar to work out the chances of thunderstorms in your area.
Organisations around the world use satellites, drifting and moored buoys, ships, aircraft, and land-based observation stations to monitor conditions at all times. The accuracy of marine weather forecasts has vastly improved.
CAN YOU RELY COMPLETELY ON MARINE WEATHER FORECASTS?
The short answer is no. Even modern technology cannot predict all subtle and sudden changes in weather. The reality is that there are reporting inconsistencies all over the world and collecting data from remote areas is very hard.
Plus, some phenomena, such as small-scale hurricanes and typhoons, can be extremely unpredictable. The best models are correct roughly 70-80% of the time.
This is why experts estimate that marine forecasts are relatively accurate for the next 2-4 days. The further in advance you check the weather, the less precise it will be.
The detailed data we are now used to looking at, such as wind speed, wind gusts, and wave height, aren’t exact. And a small change in wind speed or wave height can make a big difference to a small boat.
How to use marine weather forecasts
Accept that the forecast can overestimate or underestimate some of the data and that wind gusts can greatly alter sea conditions. Make a decision on heading out based on the range of conditions you’re comfortable in and leave the forecast some room for error.
For example, you may be confident heading out in up to 25 knots of wind and 2.5m waves. Head out when the forecast calls for up to 18 knots of wind, 22-knot gusts, and 2m waves. This way, if the conditions deteriorate, you still have the self-assurance and experience needed to deal with the situation. Adjust your range as you gain confidence.
If you get to your boat and the conditions don’t look favourable, don’t go out. You can always go for a walk or a drink, safely on shore.
Compare different models
Don’t like the idea of having to cancel a boat trip at the very last minute? Looking at more than one weather model will help you judge the accuracy of forecasts.
When the models are aligned, you can be fairly sure that they are precise. Feel free to make tentative plans.
If, however, two or more models disagree, you should account for a middle-ground scenario. On days like this, accept that you may get to the boat and decide it’s not safe to head out after all.
Getting familiar with the models and their area of expertise will also help you weigh each forecast. For example, ECMWF is very accurate in Europe, but not in the USA.
Sounds complicated? You don’t need to do this. You can simplify your life by checking the local marine weather forecast and trusting that expert meteorologists have estimated it to be the most accurate outlook.
Invest in a satellite phone
If you plan to be offshore for a number of days, invest in a satellite phone, so you can regularly check for weather updates. The forecast often changes every couple of days due to varying conditions. Monitoring the situation regularly will help you make plans and prepare to deal with incoming weather.
Remember: if you get to the dock and the current conditions look a lot heavier than forecast, don’t go out.
Need a refresher on how to interpret a marine weather forecast? Have a look at this article.