A YELLOW warning issued for Bournemouth, Poole and Dorset for heavy rain on Thursday has been extended.
The Met Office issued the alert, which means 'be aware', on Tuesday afternoon.
The warning was originally put in place between 3am and 7pm tomorrow but is now valid from 12.05am until 9pm.
The warning says: "Areas of heavy and locally thundery rain are expected to move north and west across the southern half of England along with Wales during the early hours of Thursday.
"A brief period of drier weather reaching the extreme southeast around midnight Thursday will follow northwestwards, probably reaching much of Wales and southwest England later in the morning.
"However, scattered locally heavy showers, with the risk of some slow-moving thundery downpours, are likely to develop quite quickly during Thursday, only slowly dying out in the evening.
"The public should be aware of the risk of localised flooding.
"This warning has been updated to extend it to all of Wales and the southern half of England. There remains considerable uncertainty in the rainfall details and further updates may be issued."
A spokesperson for the Met Office added: "An active complex frontal zone is expected to move northwards into southeast England on Wednesday evening continuing across the southern half of England and Wales on Wednesday night into Thursday morning.
"To the rear of the frontal zone scattered thundery showers are likely to develop bringing some further localised downpours during Thursday afternoon.
"Considerable local variations in rainfall are likely. However, totals of more than 40 mm are likely in places through the day with a risk of 15 mm falling in less than an hour locally."