Parts of the UK are being hit by very heavy rain and winds of up to 50mph (80kph) - as more than two million Brits head overseas on holiday.
Yellow warnings for rain and wind are in place for the East Midlands, East of England, southwest England, London and southeast England, warning people to "be aware".
The Met Office warnings are valid from noon on Friday until 9am on Saturday.
Sky News Weather Producer Christopher England said a month's rainfall is possible in some places on Friday, with a risk of localised flooding.
It comes as what has been billed as the "Great Summer Getaway" begins.
The Association of British Travel Agents (ABTA) estimates that 2.1 million holidaymakers are set to head abroad, with Heathrow Airport expecting its busiest ever day on Friday.
Officials at the west London airport are expecting more than 500,000 passengers to travel through this weekend, including a record-breaking 131,046 on Friday.
Spain remains the destination of choice for UK holidaymakers, although a strike planned by Spanish Air Traffic Control services over the weekend could cause problems.
Other eurozone countries, including Cyprus, France and Greece, are also popular as the pound is at an eight-year high against the euro.
The most popular long-haul destination is Florida, the ABTA said.
An ABTA spokesman said the wet weather might tempt more people to make a last-minute booking.
Other airports are likewise expecting a busy weekend.
A total of 310,000 passengers are expected to fly out from Gatwick, 160,000 from Stansted and 342,000 from Manchester.
In Scotland, an estimated 100,000 passengers will depart this weekend.
The ABTA spokesman added that with many airports predicting record numbers, holidaymakers should leave plenty of time to get to the airport as the roads will be "extremely busy".
Those travelling by public transport should check for any potential engineering work.
Air traffic controllers at NATS have been preparing for weeks to ensure flights get away safely and with the minimum of delay, adding that routes to all the usual holiday destinations in Spain, the Canaries and southern Europe are expected to be busy.
Roads and ports are expected to be busy as well.
The RAC estimates 2.3 million people will hit the road on Saturday, and Channel Tunnel operator Eurostar estimates 71,000 holidaymakers will leave for Paris and the south of France this weekend.
Motorists heading to France have been warned they face disruption on major routes due to action by farmers.
The AA said it had received reports from its control centre in Lyon of delays on the A6/A7, known as the Autoroute du Soleil, a major route for UK tourists travelling to the south.
The disruption comes after weeks of chaos on both sides of the Channel because of protests by French ferry workers and problems with migrants trying to reach the UK.
RAC spokesman Simon Williams predicted "road misery" in the UK, and called on motorists to stay calm.
He said: "The heavy and persistent rain will make driving conditions challenging and there is a real risk that delays may lead to frustration behind the wheel."