Marine Glossary

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Puget Sound convergence zone

An effect known well to Puget Sound sailors in which a southerly wind reverses to a northerly wind with a brief period of calm air, rain, and clouds between them. Sometimes the wind reverses in the other direction if the zone moves north instead of its more usual slide down the Sound to the south. It comes about when a westerly wind on the Washington Coast sends wind eastward around the top and bottom of the Olympic mountains.

This creates a northerly in the north sound and a southerly in the south sound and a convergence zone of rising air, with calm (horizontal) surface wind, rain, and clouds where they meet, generally in the vicinity of Admiralty Inlet. In extreme cases, the winds can be at 20 knots when they switch, but they are more often less than that. Studies have shown that a convergence is most likely when the coastal winds are between 260 and 320 at speeds of 5 to 15 knots for a period of at least 4 hours.

These precursor conditions are available to mariners from the VHF reports for the station at Forks, WA. Convergence can happen throughout the year, but is most likely in April, May and June, when 2 to 4 major events per month occur.