The yellow 'be aware' warning for strong winds replaces a warning issued on Tuesday for heavy rain. The warning is valid all day today.
The Met Office said: "Another spell of unsettled weather is expected on Friday with further wet and windy conditions likely across western areas in particular.
"Tides will be very high, and the public should be aware of the risks of large waves and coastal flooding."
The Met Office chief forecaster added: "Winds will gust to around 50-60 mph over coasts and hills. Whilst this is not especially strong, lowering pressure will combine with high tides around the UK coastline and bring the risk of some flooding."
*The Met Office updated the warning today (Friday), forecasting heavy showers and thunderstorms, with hail and squally winds, in southern parts of England and southern and western parts of Wales during the rest of today.
It said people should be aware of the risk of disruption, particularly to travel, with the possibility of localised surface water flooding, hail temporarily covering roads and also damage from lightning strikes.
The chief forecaster said: "A deeply unstable airmass covers the UK with bands of heavy showers and thunderstorms moving northeastwards, particularly affecting southern parts of England and southern and western Wales.
"The showers could produce 5-10 mm of rain within an hour."
A further warning has been issued for Sunday, when heavy rain is expected, according to the Met Office.
The yellow, be alert, warning is valid from 9am to midnight.
The Met Office warned: "Outbreaks of rain, heavy at times, will affect the UK on Sunday.
"Quite widespread accumulations of 10-20 mm are then likely with locally in excess of 40 mm possible over some higher ground.
"This additional rainfall, following the recent wet weather, means that the public should be aware of an increased risk of both surface water and river flooding as well as disruption to transport.
The chief forecaster said: "Another spell of wet and windy weather will affect the British Isles on Sunday as a new, deep depression becomes anchored over the eastern Atlantic Ocean. The associated frontal system is then expected to move eastwards across Britain, perhaps not clearing the far east and southeast until Monday morning."