The heatwave has spurred people into splashing out on fans, food and drink, but it has failed to prevent a slowdown in spending growth, a survey suggests.
Sales in stores open at least a year rose by 0.5% in July, compared with 1.1% in June, the British Retail Consortium (BRC) said.
The slowdown came despite food sales having their best July for five years.
BRC chief executive Helen Dickinson said for many struggling retailers "autumn could not come sooner".
She said the recent sweltering temperatures had put shoppers off browsing in shops, while the three-month long period of sunshine meant demand for many summer products had slowed.
The survey also showed that total sales slowed last month, rising 1.6% compared with 2.2% in June.
Paul Martin, UK head of retail at KPMG - which helped to produce the BRC survey, said "perhaps it was just too hot to hit the High Street".
However, he said the survey showed the challenges retailers were facing, warning it would take more than "events-based retail and sunshine to improve the health of the High Street".
The gloomy findings suggest little let-up in the tough retail climate.
House of Fraser is urgently seeking fresh funding in order to survive, with experts warning it will collapse if it does not find a new investor.
The department store chain is one of a number of retailers struggling amid falling consumer confidence, rising overheads, the weaker pound and the growth of online shopping.
Electronics chain Maplin and toy chain Toys R Us both collapsed into administration earlier this year.
Other High Street chains such as Mothercare and Carpetright have been forced to close stores in order to survive.
A separate survey from Barclaycard, which sees nearly half of the nation's credit and debit card transactions, suggests a slightly less negative picture.
It said consumer spending rose 5% year-on-year in July.
Spending in pubs was up almost 17%, the biggest increase since April last year, a rise Barclaycard credited to England's World Cup performance.
However, it too cautioned that the rise in spending was likely to be short term with consumers less confident in their household finances than a year ago.