Guide to marine weather forecasts: chapter 7

Forecast Updates - When and Why

Forecasts are updated as needed when the difference between the forecast and actual conditions are such that the security or safety of mariners is at risk, or when the difference between forecast and actual conditions poses a hindrance to normal marine operations. Updated forecasts will only include the marine areas to which the update applies.

Regular marine forecasts will be updated when one or more of the following criteria are met:

• An unexpected change in marine weather conditions that affects the status of a warning or watch.
• For wind speeds below 60 knots: If the highest sustained wind speed is observed or is expected to differ from the forecast wind speed by 10 knots or more.
• For wind speeds equal to or greater than 60 knots: The highest sustained wind speed is observed or is expected to differ from the forecast wind speed by 15 knots or greater.
• For wind direction: If the observed or expected wind direction differs from the forecast wind direction by greater than 45 degrees when observed or forecast wind speed is 20 knots or greater.
• If any marine weather conditions such as visibility or wave height differs significantly from observed or expected conditions, the forecaster may issue an updated forecast.