Brits are set for thunderstorms and gusts up to 50mph but it is expected to be warm for the rest of the week with 22C highs.
Most of the UK had plenty of sunshine on Tuesday with the mercury rising to 20C in Sussex but in Shetland it did reach just 10C due to a high pressure that has now moved away.
And looking to Wednesday more unsettled conditions are expected as a slow moving low pressure system moves in from the west bringing wind and rain.
At the same time it will be warm for the time of year, and in the south west it could be 16C in the early morning of Wednesday - hotter than it should be during the middle of the day. While the mercury could peak at 22C in the Channel islands.
BBC forecaster Ben Rich said: "Tuesday was a fine and mostly sunny autumn day for many of us but the next few days are looking a little different. The change is being brought about this swirl of cloud. Now this is an area of low pressure and it is trapped in a dip in the jet stream.
"It will bring some outbreaks of rain at times but it will also bring some quite warm air for us, notice northern parts will stick with something a little bit colder as we go through the day on Wednesday.
"So this is how Wednesday shapes up with that area of low pressure throwing some showers and thunderstorms northwards although they will tend to weaken the further north they get. Parts of eastern Scotland, north east England seeing quite a lot of cloud, the best of any sunshine likely to be across south and eastern England.
"It will be windy … the gusts particularly for parts of west Wales could be stronger … up to 45mph or 50mph. Warm in the south in fact 22C for the Channel islands, cold in the north just 10C for Aberdeen.”
For Thursday morning it is expected to be a wet start with showers and thunderstorms overnight.
“Through Wednesday night and into Thursday we will see further heavy downpours pushing northwards, there could well be some thunder and lightning, it could be a really wet start to Thursday morning across parts of Eastern England, could be a bit of fog around in places, some low cloud," said Mr Rich.
Then the outlook for the rest of Thursday and the coming days is for more rain, thunderstorms and possibly gales.
UK 5 day weather forecast
Today:
Showery rain, heavy for some with possible thunderstorms, affecting Northern Ireland, Wales and southern, western and central England but some brighter warmer interludes in the south. Drier and brighter further north and east. Windy and gusty, especially in the west.
Tonight:
Rain crossing northern areas, another area of heavy rain affecting parts of the west, particularly Northern Ireland. Parts of south, central and western England drying up with patchy fog. Mild.
Thursday:
Rain clearing northern Scotland, another batch moving north across parts of eastern England, perhaps heavy. Further showery rain reaches the southwest by evening. In between, brighter, drier and reasonably warm.
Outlook for Friday to Sunday:
Continuing unsettled with further showers or longer spells of rain for most, some heavy. Windy at times, especially in the southwest. Remaining mild or very mild, especially in the south.
