Gary, at the risk of reposting stuff I have done many times before, there is one FREE website that gives you excellent weather forecasts up to 7 days out. Go to...
and click on "free access to 3 - 6 days forecasts.
This gives you a chart of the UK and Eastern Atlantic. Most usefully it shows the likely wind speed and direction for up to 7 days ahead in daily charts. All you need to know that is not shown on the chart is that wind blows anticlockwise round the centre of a low and clockwise round the centre of a high pressure area.
It is impossible for a forecaste to tell you 7 days ahead if it is going to be sunny or cloudy. But that's not what you need. You need to know if it's going to be flat calm or blowin' old boots when you want to plan your trip. That you can usually tell from these charts.
I've been doing this sort of thing for a long time now and I usually get it right, I can sometimes hazard a guess 9 days out by extrapolating a series of charts that are very straightforward. It can be difficult if the weather systems are complex.
Recent ones have been fairly straightforward and my prediction for the South West cruise 9 days out was correct and I said a week ago that it is going to be blowing for the Scillies trip. With 3 days to go it looks as if that is going to be correct as well.
There is no magic to it. Just check this FREE site once a day and get a feel for what is going to happen. If in doubt for a particular date post a thread and I will help you make sense of the charts.