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 is forecast be the hottest day of the year so far but the hot and humid weather will not be everywhere and will not last long.
The sudden change in our weather is partly due to Tropical Storm Debby, which brought flooding rains to the eastern US.
Influence of Debby
Debby drenched a number of historic southern US cities earlier this week.
The storm then swept quickly north to eastern Canada, bringing the wettest day on record to Montreal. before it started to break up.
Having weakened considerably, the remnants of Debby are now heading out into the north Atlantic.
As well as bringing heavy rain Debby pushed very warm air to higher latitudes. This has changed the position of the jet stream with impacts expected in the UK.
Tropical Storm Debby changes the jet stream pattern over the Atlantic
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 very humid air will be drawn up very quickly from Spain and France.
But it will not be hot for all of us.
How hot is it going to get?
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.
On Saturday the temperature in the UK was distinctly average, but on Sunday we will see temperatures jump up by four or five Celsius in England and Wales as the Sun comes out.
Scotland and Northern Ireland will not be as warm but should stay dry. The weather could start to break on Sunday night with the threat of a few storms in the west.
Heavy rain and thunderstorms will then head eastwards on Monday but mainly for the northern half of the country.
Further south it will be a very uncomfortable night for sleeping. With the hottest air arriving from France and Spain before the cloud does, the temperature in south-east England could shoot up very quickly to 34C on Monday. Timing will be everything.
Some of the UK maximum temperatures forecast for Sunday and Monday
Once again the hot weather is not for everyone.
The heat and high humidity are focused on Lincolnshire, the 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 until Tuesday morning.
How long will the heat last?
For it to be called a heatwave the temperature criteria have to be reached for at least three days in a row.
Tuesday will still be very warm in East Anglia and south-east England with temperatures up to 27 or 28C. But next week the jet stream pattern in the Atlantic will straighten again and we will be back to more changeable weather with temperatures nearer normal.
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.
