Surface eddy and low pressure aloft maintain southerly winds.
by Mike Godsey,
Mike AT iwindsurf.com
Today, Saturday July 29 things start with a small surface eddy near the coast.
Then tomorrow a Bodega eddy, much like the one you see in my banner animation above, forms at the surface.
Then low pressure systems develop above the surface eddy cause it to grow much longer and to endure for several days.
Notice in the first animation how the North Pacific High’s surface NW winds turn more NNW as it pushes a ridge towards the Pacific Northwest.
Then notice how a small surface eddy forms west of the Golden Gate in response to the NNW winds. In recent years this eddy formation has gone from being a rare event to being a very common event. The reasons are complex and near global causation and are way beyond this blog’s scope.
But this building surface eddy is more complex than most eddies. As you can see in the 2nd. animation NNE winds 
develop aloft and a massive counter-clockwise spinning low pressure develop above the surface eddy. This causes the surface eddy to enlarge and endure for days. And the combo of all the southerly flow from these circulations pushes a deep marine layer far into the Bay Area.
More later….