UK Weather: Some parts of the UK could reach 30C, but there will be more rain

Parts of the UK could be hit by a 30C heatwave by the end of this week after an unusually wet start to July.

The heatwave is set to hit south-east England on Friday, with temperatures likely to set a new record for the hottest day of the year, after 30.5C was recorded in Wisley, Surrey, on June 26.

Areas that have so far experienced a deluge in July are now expected to become much drier and warmer, even if only for a short period.

But we shouldn’t put away our umbrellas just yet: the dry weather will be even shorter in the north-west and there could be further disruption across the UK as early as Saturday night.

The start of the month has been wet and cold for most of us, with temperatures below or just above the seasonal average. Some parts of the country, including Loftus in North Yorkshire and Northolt in London, have already recorded more than twice the average rainfall for July.

The Met Office issued a yellow warning for rain on Monday, with some areas receiving 15-20mm in just an hour and 30-40mm over several hours.

The warning was issued on St Swithin’s Day, which, as the saying goes, could mean it will rain for another 40 days.

The cool and wet July is due to the jet stream (a fast-moving wind moving high in the atmosphere) being mainly over or to the south of the UK.

Rainfall was not everywhere, however. Some areas in the north and west, including Castlederg in Northern Ireland and Machrihanish in western Scotland, were relatively dry, receiving only 20-25% of their average July rainfall.

Northern Ireland is much drier than last July, which was the wettest month on record.

The jet stream – the fast-moving band of air in the upper atmosphere responsible for propelling low pressure systems from the Atlantic – has shifted towards the south of the UK, allowing cold Arctic air to surge in from the north.

It will now move further north, deflecting rain north and west, and allowing warmer air to infiltrate once more from the south.

A high pressure system will start to form in the Azores. This means that the UK will be almost completely dry on Wednesday.

Temperatures will be close to the seasonal average, between 17 and 21°C in Scotland and Northern Ireland, between 18 and 23°C in Wales and between 25 and 30°C in England. It will of course be warmer under the July sun, which we have been missing recently.

Rain will hit Northern Ireland and western Scotland on Thursday and Friday, heralding a return to gloomy and wet conditions.

However, dry conditions could persist across much of England and Wales, where temperatures will rise slightly further, particularly in the south-east of England.

By Friday, temperatures in London could peak at 30°C, before dropping again this weekend.

Probably not – the Met Office defines a heatwave as three or more consecutive days of temperatures above a certain threshold, which varies depending on where you are in the UK.

In the London area, this threshold is 28°C. For Scotland, Northern Ireland, Wales and most of the north and west of England, it is 25°C.

If temperatures reach 25°C, it will be the first time in July in the UK.

The heat is not expected to last: a thunderstorm to the east on Saturday evening should bring temperatures back down to average.

Next week we will see westerly winds with dry spells and some sunshine, but also showers and longer periods of rain at times, especially in the north and west.