Storms could slow down the platinum jubilee festivities, and the Met Office issued a weather warning for the south of England.
Weather forecasts predict heavy rain and lightning in some places and a yellow warning has been issued from midnight until 10am on Saturday morning.
The Meteorological Office said there was a small chance that homes and businesses would be flooded quickly, with damage to some buildings due to flood water, lightning, hail or strong winds.
He also warned of a small possibility of delays and some cancellations of train and bus services due to lightning and floods, as well as possible blackouts, difficult driving conditions and road closures.
The area covered by the notice extends from Dover to Penzance and Bath and south London.
The warning was issued in the morning after it was initially believed that storms could fall on Saturday evening, during the BBC Platinum Party at the Palace.
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Some 22,000 people are expected at the star-studded event, which will feature performances by artists such as Craig David, Alicia Keys and Sir Rod Stewart.
Diana Ross will close the two-and-a-half hour show with her first live performance in the UK in 15 years.