A level three alert is in place until Sunday, after the Met Office issued it earlier in the week.
Today is set to be the hottest day with temperatures expected to exceed 30C in parts of the region.
Here is the hour-by-hour forecast for Portsmouth:
Saturday
7am – Sunny intervals – 23C
8am – Sunny intervals – 23C
9am – Cloudy – 25C
10am – Sunny – 26C
11am – Sunny intervals – 27C
Noon – Sunny intervals – 28C
1pm – Sunny intervals – 28C
2pm – Cloudy – 28C
3pm – Sunny intervals – 28C
4pm – Sunny – 28C
5pm – Sunny intervals – 28C
6pm – Sunny – 28C
7pm – Sunny – 27C
8pm – Sunny – 27C
9pm – Clear night – 27C
10pm – Clear night – 25C
11pm – Clear night – 24C