Heavy rain will spread north-east across England and east Wales into Thursday.
The Met Office yellow warning for rain covers much of southern and eastern England from midnight on Wednesday night into Thursday, and through until 21:00 BST.
Rainfall totals by early Thursday morning could be widely 20-30mm (around 1in), and for some places 30-50mm (up to 2in).
There is a small chance a few places could exceed this, most likely over Devon and Cornwall and more generally in eastern England.
Localised flooding and some transport disruption is possible.
The wind will also strengthen with an additional yellow warning from the Met Office covering west Wales and south-west England from 04:00 until 18:00 BST.
A separate wind warning has also been issued for eastern England from 09:00 Thursday until 23:59 BST.
Very strong north-westerly winds gusting to 45-55mph (70-90km/h) in both areas are possible, while locally 65mph (105km/h) on the east coast is also possible.
While there is still some uncertainty on the intensity of this weather system, the Met Office warns that there is potential for gusts up to 75mph (120km/h) for a small period of time later on Thursday morning and into the afternoon.
These wind speeds have the potential to topple trees or their branches, cause travel disruption and even bring power cuts.
