Monday, March 2, 2015

St Pete Sea Breeze - Under AP & New Day 1 Expectations

Thistles are under AP until 2 PM at the earliest.  Heavy fog in St. Pete right now.  With a stalled front just south of us and nothing in the gradient to drive a real breeze (despite the local forecast calling for a light NW later) our best shot at sailing today is a sea breeze.

For that to happen, a few things need to occur.  We need the fog to burn off.  Then the land needs to heat up.  Clues that the sea breeze is trying to generate include cumulous clouds generating over downtown St. Pete, birds soaring in the sky over St. Pete in the thermals, black flies in the air (less frequent in recent years it seems), and rising temps with sun.

If those things start to happen, the sea breeze will often come after the cumulous clouds over St. Pete disappear.  The sea breeze will come in as a line, often spilling around Pinellas Point to the south first.  When it first comes in there may be some right gusts as the breeze first comes over the St Pete land but it should settle in before long.  The direction typically starts around 210 and will veer (shift right) as the sea breeze matures.

Expect quick oscillations, driven by the small (<200 meter) boundary layer the sea breeze exists in.  Shift patterns are typically 2-6 minutes, which can be 1-3 minutes when sailed to windward.  If the course is in a place where the breeze flows over land first there will be added gustiness and randomness to the oscillations, but if the breeze had a long runway it should be quite steady in speed and have predictable oscillations that may even be time-able.

In a sea breeze like this you want to establish a mean number for the wind.  Once you have that number, you tack as soon as you cross that number in an oscillation.  You don't wait for the breeze to shift all the way to the maximum.  Make sure to watch for your mean number to creep to the right as the sea breeze matures.

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