Flood warnings have been issued as up to three weeks' worth of rain could batter Bath and the South West on Friday and Saturday.
Thunderstorms, hail and lightening could cause a Glastonbury mud bath and a Wimbledon washout.
Saturday's Bath Bike event could also be affected.
The Met Office forecast the downpours to start in the early hours of Friday and have estimated that up to three weeks' worth of rain could fall in some areas over three days.
A spokesperson said: "Showers will become heavy and thundery across south western parts of England and Wales early on Friday."
Rain is expected to lighten overnight on Friday with slow moving heavy and thundery downpours developing during the day on Saturday.
Downpours may lead to localised flooding and potential disruption to transport.