Wet weather is set to put a dampener on the Spring Bank Holiday weekend as sun gives way to heavy rain and high winds.
There will be a dramatic change in the weather on Sunday
The weather will be dry and sunny on Friday and Saturday, but it will worsen on Sunday and bank holiday Monday.
The AA said about 18 million vehicles will be on the roads, with Brighton, Great Yarmouth, Bournemouth, Blackpool and Newquay the top seaside resorts.
About 1.9 million Britons will travel abroad, according to the Association of British Travel Agents (Abta).
Spain and its islands is the top European destination, while Florida is the favourite for those travelling further afield.
The leading city break locations are Paris, Amsterdam, Dublin, Rome and Prague.
The weather will struggle to reach 10C (50F) in some parts of the UK by Monday.
BANK HOLIDAY HOTSPOTS
M25 around London
M6 through the West Midlands and north of Manchester and Liverpool
M5 northbound in the Midlands and southbound around Bristol
BBC weather forecaster Rob McElwee said: "It will be a fine day on Saturday. On Sunday as a low pressure develops off Ireland it will rain and rain and the wind will pick up, mostly over England and Wales, and it will touch southern Scotland.
"Temperatures will fall from 18C (64F) to more like 9C (48F) or 10C (50F), with persistent rain and howling winds."
For Northern Ireland and the rest of Scotland the weather will be changeable over the weekend.
The AA said traffic jams are set to be 33% worse than normal on Friday, 25% worse on Saturday, and 10% worse on Monday.
According to the motoring organisation, the busiest airports will be Gatwick, Heathrow, Stansted, Manchester and Luton, and the busiest cross-Channel routes will be Portsmouth, Dover and the Channel Tunnel.
The Highways Agency said roadworks at 44 sites in England were either suspended or completed by 0600 BST on Friday in time for the bank holiday, although 43 will remain.
BUSIEST UK SEASIDE RESORTS
2. Great Yarmouth
The agency's director of traffic operations, Derek Turner, said: "We are lifting as many roadworks as we can and giving drivers information about road conditions through our website, information points at motorway service areas and through travel news broadcasts."
Sports fans will be travelling to football's play-off finals at Wembley, the Scottish Cup final in Glasgow and the second cricket Test match in Leeds during the bank holiday.
Airports operator BAA said more than 1.5 million passengers will use Heathrow, Gatwick and Stansted over the weekend.
A normal weekend timetable will operate on the railways, although some services will be affected by engineering work.