The temperature in West Sussex today will rise to 30 degrees Celsius, predicts the Met Office.
There is a 60 per cent probability of heatwave conditions between midday today and tomorrow evening.
There will be high levels of UV and a ‘Level 2 - Alert and Readiness’ heat health warning for West Sussex has been issued.
From the Met Office site: “Heatwaves can be dangerous, especially for the very young, very old or those with chronic diseases.”
Temperatures are expected to peak in some southern and eastern areas today with a humid feel and staying warm and muggy tonight.
High temperatures are likely to continue on Friday in some eastern and southeastern parts of England.