More heavy rain and gusts of 50mph are forecast to hit the UK - a day after storms ended the heatwave and disrupted travel for many.
A yellow weather warning for wind and rain is in place for southern England and Wales until 15:00 BST.
The gusts are forecast for exposed coasts and hills while 80mm of rain is possible in the Brecon Beacons and Dartmoor, the Met Office said.
Flooding was possible and large waves likely in coastal areas, it added.
On Saturday evening, travellers continued to face delays at Eurotunnel and ferry terminals in Dover.
BBC Weather forecaster Matt Taylor said there had been a "drastic change" from the UK heatwave to cooler, wetter and windier conditions.
Saturday was the first day that nowhere in the UK had temperatures above 25C since 23 June.
He said the cooler conditions would continue over the next few days, but added that it "doesn't meant that summer is done with us yet".
The thunderstorms, which started on Friday night and continued on Saturday, brought the first significant rainfall for weeks to the UK.
On Saturday more than a month's worth of rain fell within a few hours in Northern Ireland, with homes flooded in County Antrim.
On one of its busiest weeks of the year, cross-Channel operator Eurotunnel said it was taking time to bring back carriages after they were removed from service during hot weather on Friday because of air-conditioning issues.
On Saturday evening,
customers travelling from the UK were departing within one hour of their booked departure time.
Customers travelling from the UK are departing within one hour of their booked departure time; the same applies from Calais. We'll give a further update at 09:00 tomorrow, until then please follow 24/7 updates here https://t.co/3GQJriovVH— Eurotunnel Le Shuttle (@LeShuttle) July 28, 2018
there were long queues into the port of Dover, with some taking three hours to get through border checks.
#PODover : Please be advised that there are long queues on the approach roads into the Port and it's taking approx. 3 hours to get through Border Checks. Rest assured that if you miss your sailing we'll get you on the next available ferry. We're very sorry for your wait.— P&O Ferries Updates (@POferriesupdate) July 28, 2018
Flights from Edinburgh, Birmingham, Luton and Stansted were delayed on Saturday and some cancelled after temporary restrictions were put in place during thunderstorms across Europe on Friday.