Could a tropical storm be about to bring the UK a mini-heatwave?

Image source, PA Media

For most of the summer the weather has been fairly average at best. However, there is another burst of heat to come this weekend.

Monday could be the hottest day of the year but the hot and humid weather will be very limited and will not last long.

The sudden change in our weather is partly due to Tropical Storm Debby, which is currently bringing flooding rains to the eastern US.

Debby drenched a number of historic southern US cities earlier this week.

The storm is now going to sweep quickly north to eastern Canada, where it will weaken and break up.

Debby is not heading to our shores but will affect our weather in a couple of days’ time.

As well as bringing heavy rain it will push very warm air to higher latitudes. This will then start to change the position of the jet stream.

Downstream, in the Atlantic, the jet stream pattern changes from straight to buckled (or more amplified). That means that by Sunday it will be positioned to the north-west of the UK. A southerly breeze will develop, and very hot and muggy weather will be drawn up very quickly from Spain.

But it will not be hot for all of us.

The highest temperature of the year so far is 32C recorded in London at the end of July. That temperature could be exceeded on Monday.

Currently temperatures are distinctly average, but in England and Wales we will see them jump up by four or five Celsius as the Sun comes out on Sunday.

Scotland and Northern Ireland will not be as warm, and rain develops here later on Sunday. The rain could turn heavy and thundery on Sunday night before it heads eastwards on Monday.

If the hottest air arrives from Spain before the rain does, the temperature in south-east England could shoot up very quickly to 33C on Monday. Timing will be everything.

Once again the hot weather is not for everyone.

The heat and high humidity are focused on Lincolnshire, East Midlands, East Anglia and south-east England. Temperatures further north and west could actually fall a little on Monday because of rain and thunderstorms.

A yellow heat-health alert has been issued by the UK Health Security Agency for the Midlands and southern England for 48 hours from Sunday morning.

For it to be called a heatwave, the temperature criteria have to be reached for at least three days in a row.

But by Tuesday the jet stream pattern in the Atlantic will have straightened and we will be back to more changeable weather with temperatures nearer normal. So let’s call it a “mini-heatwave”.

We’ve seen a few of these “heat spikes” this summer.

I’ve noticed over many years of presenting the national weather forecast that it used to be the case that we needed three or four days of dry weather to lift the temperature to 30C.

Are things changing and these temperature rises happening more rapidly?

It is difficult to quantify a shift like this, but it could be that we are seeing another impact on our weather patterns as a result of climate change.