The Met Office has warned of a risk of thunderstorms and torrential downpours in the Glastonbury area later on Thursday.
More than 200,000 people are descending upon Worthy Farm for the first Glastonbury Festival in three years, with gates having opened to the first revellers on Wednesday morning.
The first day was met with fine conditions, with temperatures of around 26C, and Thursday looks set to begin in a similar vein.
As the day wears on, however, the weather is expected to turn, before rain and thunder dominate over the weekend.
"Our advice that you should plan for both sunhats and raincoats for this year's festival remains," said the Met Office's chief forecaster Neil Armstrong.
"The warm and sunny conditions continue on Thursday, but there will be an increasing risk of thunderstorms through the afternoon and evening which bring a risk of some torrential downpours."
Thursday marks the opening of some of Glastonbury's smaller stages ahead of the main stages opening on Friday.