From the National Weather Service
A special marine warning is issued for winds 34 knots or more which could last for up
to several hours. These often are issued as a result of strong thunderstorms moving off the coast.
When a severe thunderstorm warning is issued for coastal areas, winds of 50 knots or more are
likely along with hail and dangerous lightning.
Should you be just offshore in your boat, you must be prepared for even higher winds since
the relatively flat sea surface promotes faster wind speeds. If skies darken, especially to your west,
you should seek shelter from what will most likely be southwest to northwest winds. You must take
action well before a severe thunderstorm arrives because visibility will typically drop to zero
in torrential rain, making landfall difficult.
If you are caught at sea, the dangerous winds should only last about one-Half hour.
However, they can be strong enough to overturn outboard boats and small powerboats.
Sailboaters must remove nearly all sails and keep only the smallest of storm sails.
If you do reach shelter, the safest place would be at a substantial mooring or on an anchor
with extra anchor rode scope.
