Expect a water temperature of 16 to 18 deg
You will all have your favourite weather sites, but here is a short list myself and a few friends use.
http://www.bbc.co.uk/weather. Just take care with its wind forecast for Hayling Island, as it represents inland wind speed so is under-represented. The Met Office site http://www.metoffice.gov.uk/weather/europe/uk/uk.html and click on Central Southern England. http://www.windguru.cz/. UK Hayling Island appears on their list of locations
http://magicseaweed.com/ Look for UK West Wittering as the nearest location. http://www.franksingleton.clara.net/ is a useful portal to other weather sites.
The other particularly useful one is not a forecasting site, but is a weather-measuring site. The instruments are mounted on Chichester Bar Beacon – one of the markers as you go out of the harbour, so they are within a couple of km of the race area. Wave heights in the race area are generally a bit less than indicated on Chimet because of the shallow water around the site of the instruments. The website is built by local sailors for local sailors.
http://www.chimet.co.uk/ . It is also available in summary form for mobile phone
http://www.chimet.co.uk/wap so you can see what its doing in Hayling Bay from your bed