The Met Office has issued a yellow weather warning for the whole of East and West Sussex.
The warning runs for the whole day and states that heavy rain and thunderstorms could lead to a small chance of flooding and disruption.
In a statement the Met Office said: "15 to 25 mm is likely to fall quite widely, and there is potential for 40 to 60 mm to fall in a few places."
Thunderstorms are set to hit Eastbourne, Hastings and surrounding areas at 4pm today while further west along the Sussex coast Worthing and Chichester will experience thunderstorms around 6pm.
Hail has also been forecasted for Worthing at 7pm.
Away from the coast, Crawley, Horsham, and Mid Sussex are set to experience heavy rain at 7pm.
As usual, drivers are urged to take care when driving due to excess surface water, spray and flooding.