Reduce sail before the squall line hits... If possible, get to an area where the you're in the lee of the shore, so the force of the squalls is weakened. If near a lee shore... head for deeper water and further from shore. Rig jacklines and put on your PFDs, harnesses and tethers if you've got them.
PDF's will either already be on or very close.
I'm confused about the leward vs. winward shores. Which side is leward? the side that the wind is blowing TO... correct? Wouldn't that be where the larger waves would be though?