John Lewis said the unsettled weather drove footfall and boosted sales by 9.3% for the week ended August 9.
Fashion sales were up 13.7% over the week with womenswear performing strongly. The team managing "Sale or Return" brands (John Lewis' version of department store concessions) were also commended as new partner brands were a hit with customers.
John Lewis said it expected back to school kidswear sales to have a late surge this year.
Barry Matheson, head of selling development at John Lewis, said: "Reading the trading comments from John Lewis Direct and the branches this week brought a smile to my face. They were wonderfully upbeat and rightly so, with the division finishing well ahead of last year. While the comparisons against us were softer than of late, that in no way detracted from the strength of the performance given the extremely challenging trading conditions we are in."
At John Lewis' individual stores, sales at London's Oxford Street rose 16.3% on a year earlier and sales at Aberdeen were up by 8.1%. Shopping centre Bluewater saw an increase of 6.7% while the Trafford Centre store in Manchester was also up by 6.9% and Milton Keynes was ahead by 12.6% .