I’ve listed below those websites and suppliers that I have found particularly useful. Obviously I can’t take any personal responsibility for your experiences with them.
The Royal Yachting Association
A good start for any questions you have about sailing in the UK Weather Information: in addition to the normal Met Office info I have found the following sites incredibly accurate and helpful, as they allow 3 hourly breakdowns and include wind, swell, visibility, and rain.
My favorite weather site. It allows you to see 3 hourly accurate views of coastline and open water crossings. As well as wind it shows swell, airpressure, visibility, cloud cover and precipitation. I’ve always found it too be very accurate over a 3 day timescale.
My second favorite weather site. I use this one for local coastal hops, particularly when I want to check wave heights. It is very good for specific very local weather. Think of the places that surfers might go!
Professional Yacht Deliveries
This is the delivery company that I have done nearly all of my deliveries for. Not the cheapest, but the level of support and knowledge are superb. They have great client and supplier contacts, as well as an enormous list of skippers and crew.