Friday, May 21, 2010

Coastal convergence

Clyde catches a surf ride

Seven of us were out yesterday evening for a bit of practice in the wind and waves. The low laying clouds were blowing past us from a SSE direction. Wind waves were coming at us from the SW. It was a classic case of coastal convergence.

Wind behaves differently over land and sea. The direction of the wind can vary between land and sea because the land causes more friction than does open water. When the wind is aft and the coast is to starboard these different angles of surface winds converge and cause a band of wind that's 25% stronger. Friction caused by the shoreline keeps coastal wind speed lower than those just offshore.

That's why the wind forecast sometimes says "winds 30, gusting to 50 except 70 near the coast".

That is precisely what we experienced last evening. After beating into the wind a few times to catch surf rides back downwind, I paddled upwind hugging the shoreline where the wind was less severe, paddled offshore in the beam seas and surfed back.

After 2 hours I was content and went home, another lesson learned.

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