Be Your Own Expert Weather Forecaster

Building your own bespoke forecast is the best way to get reliable weather updates with which to make sound decisions at sea. Toby Heppell finds out how the experts do it

Forecasts are flawed. Weather forecasts online, on an app or from the Met Office via VHF radio, are all subjective. Inshore waters or shipping forecasts are limited by brevity, large areas and a high degree of caution – they often forecast stronger winds than you may experience. Mobile apps lean towards forecasts for specific locations and so don't give you the big picture. Some are created for specific purposes such as surfing or farming and have a level of interpretation; without access to the algorithms behind them, however, it's almost impossible to work out what the built-in bias may be.

Often these forecasts are accurate, but sometimes they will be wrong. If you’re using someone else's forecast, you won’t know the reasons why it was inaccurate. Expert navigators and meteorologists build their own forecasts so they are in control of the subjective elements or variables. Learning to do this means you can judge if a forecast is accurate or reliable, and make your own informed forecasts for the precise route and time you plan to sail. If you get it wrong, you can learn from your mistakes and make better-informed decisions about when to put to sea and what conditions to expect.

To do this, you'll need to be able to access and read GRIB files (Gridded Information in Binary), which have been around for years, but are always getting more accurate, read them, and get an idea of the broad weather picture. You will need to interrogate highresolution GRIB files for problem spots using your understanding of local weather effects, and compare this overall picture to other sources of forecast to judge your assessment.

This is a skill that takes time to hone, but develop your skills over time and you will be able to make expert-level judgments about the weather, and know how to judge which forecasts you can trust or not.

ABOUT GRIBS