Where are you going? It will still be hot and the rain will be warm! I remember swimming in a pool in Greece and it was soooooooo cloudy it was ridiculous - also got REALLY burned that day even with no sign of sun at all so be careful!
We had similar experiences with holidays in Britain - basically it rained wherever we went, so we decided to go to the Vendee (as you say, smugmum, supposedly the second sunniest part of France), in the hopes of some sunshine, and it bloody rained there, more than half the days we were there.
Even when we went down to the Cote D'Azur, we didn't escape the rain altogether - we did get lots of lovely hot sun, but at least once each holiday, the heavens opened and we had spectacularly large amounts of rain.
'Tis sunny in our bit of scotland today, though....
unfortunately you will not get much more sun / heat on the western coast of france as they are near the atlantic which is the cause of the crap weather in this country. if you want guaranteed good weather then make sure to go somewhere bordered by the Med!
Went to the Vendee to a mobile home in August 98. Think we had 5 good days out of 14. Used to hear the rain falling on the caravan roof most nights. The campsite potholes in the road were constantly waterlogged. We spent £1600 on that holiday, having holidayed mostly in the UK until then as we couldn't afford abroad. After that we did 5 years in Majorca where we could 95% of the time guarantee the weather.