1. What do the symbols on the wind forecast charts indicate?
2. What weather data do you use to produce your weather charts?
3. When are the weather charts updated?
4. What does UTC time mean?

1. What do the symbols on the wind charts indicate?

These symbols are called "wind barbs", and they indicate both the wind speed and the wind direction.  The wind direction is indicated by the angle of the barb, with the barb "flowing" from the wind direction. The speed of the wind is represented by the number of lines and/or flags on the tail. Each full line equals 10 knots and a smaller half-line is 5 knots. A flag (triangle) is equal to 50 knots. Every item should be added together to determine the speed of the wind.

In each of the following examples the wind is blowing from the NW:

2. What weather data do you use to produce your weather charts?

The weather data that we use to produce our weather forecast charts come from the most trusted and reliable sources available.  The majority of our forecasts (surface wind, surface pressure, visibility, cloud cover, precipitation) are derived from the GFS weather model from NOAA.

The global wave forecasts are derived from the WW3 wave model from NOAA.

The Mediterranean wave forecasts are derived from the WAM4 wave model run by the Atmospheric  Modelling and Weather Forecasting Group of the University of Athens..

The Gulf Stream forecasts are derived from the RTOFS model from NOAA.

The Sea Surface Temperature analysis data comes from NOAA using satelite data from NASA.

For more information on the above data sources and models, please go to the About page.
 

3. When are the weather charts updated?

The GFS model forecast charts (surface wind, surface pressure, visibility, cloud cover, precipitation) are updated 4 times a day, at approximately 0445, 1045, 1645 and 2245 UTC.

The global WW3 wave forecast charts are updated 4 times a day, at approximately 0500, 1100, 1700 and 2300 UTC.

The Mediterranean WAM4 wave forecast charts are updated once a day at approximately 0800 UTC.

The Gulf Stream forecast charts are updated once a day at approximately 1130 UTC.

The Sea Surface Temperature forecast charts are updated once a day at approximately 1430 UTC.
 

4. What does UTC time mean?

Coordinated Universal Time (Temps Universel Coordonné) The international time standard (formerly Greenwich Mean Time, or GMT). Zero hours UTC is midnight in Greenwich, England, which is located at 0 degrees longitude. Everything east of Greenwich (up to 180 degrees) is later in time; everything west is earlier.

The current UTC time is displayed in the upper right corner of the PassageWeather website.

If using the PassageWeather forecast images when offline, the easiest way to find the UTC time is to check your GPS, which will always display UTC time very accurately.