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.
weather.gov 
