Scattered thunderstorms this evening and early Wednesday could lead to some power cuts and travel delays in Portsmouth and Hampshire.
The Met Office has said there is a small chance of damage to property from lightning strikes, hail or strong winds
Portsmouth is due to temperatures of around 29C from 4pm today and in Gosport it is expected to get up to 30C.
Humidity, pollen and UV levels are due to be high across the UK and a level 3 heatwave has been issued for Portsmouth and Hampshire with experts encouraging people to stay in the shade and drink lots of water.
A level three heatwave is one level away from being considered an emergency situation.
Ruth May, chief nursing officer for England, said: ‘Like lots of people I'm looking forward to having fun in the sun with family and friends this weekend, but nobody wants to spend a pleasant day stuck in a hospital or urgent treatment centre.
‘It's really important to take simple precautions like drinking plenty of water, using high-factor sunscreen and remembering to take allergy medication if you need it – as is making sure to check in on neighbours and loved ones who can suffer the most from heat and pollen.’