Portsmouth weather: Hour by hour forecast amid thunderstorm and heat warnings over city and Hampshire

The UK Health Security Agency (UKSHA) has issued a yellow heat alert for Portsmouth and south east of England across this weekend. It will be in place until 9am tomorrow morning (September 2).

“Minor impacts are probable across the health and social care sector”, the UKSHA previously said, “including Increased use of healthcare services by the vulnerable population and an increase in risk of mortality amongst vulnerable individuals and increased potential for indoor environments to become very warm.”

Alongside this, the Met Office have implemented a thunderstorm warning for Portsmouth, Hampshire and other parts of the UK. Starting in 4am, this will be place until midnight. The forecaster said there is a “small chance of flooding and disruption from heavy showers and thunderstorms” in a few places.

They added: “A few showers and isolated thunderstorms are expected to develop across parts of southern England on Saturday night, but by Sunday morning there is an increasing risk of more active and organised heavy showers and thunderstorms moving in to, or developing across, parts of southern England.

“The risk of storms will then steadily transfer broadly northwards through the afternoon and into the early evening. The extent of these thunderstorms is very uncertain, and many places will miss them, but where they do occur, 30 to 40 mm of rain may fall in less than an hour with perhaps over 75 mm in one or two places, leading to a chance of flooding and disruption. Frequent lightning strikes and hail will be additional hazards, most likely across southern and central England.”

Temperatures are expected to remain in the low 20sC throughout the day. There is a small chance of rain at different times, with little thunder. High levels of humidity have been forecast amid mostly cloudy weather, with pockets of sunshine.

Hour by hour Met Office forecast

9am - Thunder - 18C - 20 per cent chance of rain - 88 per cent humidity

10am - Cloudy - 19C - 50 per cent chance of rain - 91 per cent humidity

11am - Cloudy - 19C - 40 per cent chance of rain - 92 per cent humidity

12pm - Sunny Intervals - 20C - 20 per cent chance of rain - 90 per cent humidity

1pm - Sunny Intervals - 21C - 10 per cent chance of rain - 85 per cent humidity

2pm - Sunny Intervals - 22C - 10 per cent chance of rain - 82 per cent humidity

3pm - Cloudy - 23C - 10 per cent chance of rain - 78 per cent humidity

4pm - Sunny Intervals - 22C - 10 per cent chance of rain - 79 per cent humidity

5pm - Sunny Intervals - 22C - Less then 5 per cent chance of rain - 80 per cent humidity

6pm - Sunny Intervals - 22C - 10 per cent chance of rain - 82 per cent humidity

7pm - Sunny Intervals - 22C - 10 per cent chance of rain - 85 per cent humidity

8pm - Partially Cloudy Night - 21C - 20 per cent chance of rain - 87 per cent humidity

9pm - Partially Cloudy Night - 20C - 30 per cent chance of rain - 90 per cent humidity

10pm - Cloudy - 20C - 30 per cent chance of rain - 92 per cent humidity

11pm - Cloudy - 20C - 20 per cent chance of rain - 93 per cent humidity