In reply to BillyDavies:
The Eight Kings, The Pulpit Inn, The Cove House Inn?
There's not much that avoids the rain really. Depending on the wind direction you can sometimes get away with things in light drizzle, with tomorrow's forecast wind from the west the east coast is your best bet, if the forecast rain doesn't amount to much you may get something done. TBH I wouldn't make much of a journey based on the current forecast
With a marginal forecast worth checking the Portland Heights webcam before setting out:
http://webapps-wpbc.dorsetforyou.com/webcams/pages/layout.aspx?cam=heights
The isle does sometimes "get away with it" even when there is rain in Weymouth.