About High Seas Forecast (HSF)
The 48 hour text forecasts are prepared every 6 hours for both the North Pacific and North Atlantic. The initial conditions, based on the surface analysis, satellite interpretation, and SSM/I describes winds and seas associated with significant extratropical and tropical cyclones across the warning area. The first part of the High Seas Forecast (HSF) describes WARNINGS in affect for systems with sustained winds of 34 knots or greater. The term "Gale" refers to extratropical lows with maximum sustained winds averaged over a ten minute period, momentary gusts may be higher ranging from 34 knot (39 mph) to 47 knots (54 mph). A "Storm" refers to an extratropical low with winds sustained over a ten minute period, momentary gusts may be higher of 48 knots (55 mph) to 63 knots(73 mph) . Hurricane Force refers to a extratropical low or an area of sustained winds (averaged over a ten minute period, momentary gusts may be higher) in excess of 64 knots or higher(74 mph).
The expected trends, movement and 24 hour, 48 hour forecast position and conditions are described. The forecast has less detailed information than the Offshore Waters Forecast.
The second part of the HSF consists of the SYNOPSIS AND FORECAST section, which describes weather systems which don't meet the warning criteria. Highlighted in this section are weather systems producing winds of at least 25 knots and seas of 8 feet. The message describes the initial, 24 hour and 48 hour forecast positions along with associated conditions if appropriate.
In addition the SYNOPSIS AND FORECAST may describe areas of dense fog reducing visibility below 1 NM, areas of significant structural icing, and the expected conditions for the next 48 hours.