Check Windguru, Magic Seaweed etc for local conditions - much more applicable to inshore boaters - if it is actually (technically) 'rough' then you would be foolish going out in a SIB, regardless guessing you have a good anchor, LJs, flares, VHF etc and someone who knows when/where you are out/back.
I spent all today along the coast from Hastings to Bexhill - at first the forecasts were out a fair bit and I was gutted I choose the bike rather than the SIB, however two hours in the kite surfers were in there element and it grew to a F5+ with some very nasty chop - things change quickly in the UK...
Met office gives a very general overview but things are pretty changable and non-SIB friendly at present:
http://www.metoffice.gov.uk/weather/...ecast.html#All