Bargain-hunters are expected to brave the bad weather today to match Boxing Day spending in stores with another £2.2 billion of retail sales predicted across the UK.
Shoppers were out in force yesterday, with 13.3 million people estimated to have turned out for the start of the clearance sales, up 2% year-on-year, according to the Centre for Retail Research (CRR).
The CRR said £2.2 billion was spent in stores yesterday - 5% up on last year - and it predicted the same amount will be splashed out in the second day of the post-Christmas sales, with around 13.5 million people likely to hit the shops.
But the heavy rain and gales could put off many shoppers, who are set to turn to the internet instead.
The CRR estimates that up to £370 million was spent online on Boxing Day, which could rise to £450 million today.
Joshua Bamfield, director of the CRR, said: "Depending on the weather, we might get 13.5 million people going shopping today, but we think the storms will mean people only go for a short time and could head home early."
Many keen shoppers started queuing before dawn yesterday to ensure they were first in line when the shops opened, with international tourists spending big.
Tax-free shopping experts Global Blue said shoppers from Qatar spend the most on average per transaction (£1,714), followed by those from the United Arab Emirates (£1,372), although Chinese shoppers are the biggest spenders overall.
They spend £1,367 on average per transaction, but are more likely to return to the tills with more goods.
An increasing number of shoppers went online to begin searching for early bargains on Christmas Day, with CRR predicting £250 million was spent over the internet.
Department store group John Lewis said it saw a 19% rise in Christmas Day sales - with a record 76% of orders made on smartphones and tablet computers.
The group, which releases its five-week trading update on January 2, said sales in the week to December 21 were up 4.2% on last year at £164.4 million - breaking the £160 million mark for the first time.
Howard Archer, chief UK and European economist at IHS Global Insight, said: "The initial healthy news reinforces the suspicion that the clearance sales will be strong this year - at least early on - as still squeezed consumers will be extremely keen this year to take advantage of genuine bargains in the clearance sales."
But he added: "Interest in the sales could fall away pretty quickly once the best of the bargains have gone. This would put pressure on retailers to cut prices even more, thereby further hurting their margins."
Steven Madeley, centre director for St David's in Cardiff, said he expected the shopping centre to be even busier than Boxing Day.
"The sales got off to a great start in Cardiff yesterday, with over 150,000 bargain hunters visiting us at St David's," he said.
"Today and tomorrow are likely to be even busier as stores open for longer and retailers begin to slash prices even further.
"We think up to 200,000 shoppers will visit us today and shoppers could spend up to £2 million."
Meanwhile, managers at Cabot Circus in Bristol were predicting around 100,000 shoppers would hit the Christmas sales.
Centre director Stephanie Lacey said: "Today should be one of the busiest days of the sale and we're expecting around 100,000 shoppers at Cabot Circus.
"Boxing Day was very successful for us as key retailers like Harvey Nichols and Next went into sale.
"Customers were queuing outside Next from 3am."