Temperatures are forecast to rise as high as 30C in parts of the UK as a potential heatwave develops across the long bank holiday weekend.

Heat health alerts, external have been issued by the UK Health Security Agency (UKHSA) - in association with the Met Office - across much of the Midlands and south-east England valid from 09:00 Friday 22 May until 17:00 Wednesday 27 May.

The mercury is set to creep up each day for the remainder of the week before the warmest weather of the year so far settles in.

If readings reach 30C before Monday, it will be the earliest date this has happened in the UK for over 70 years.

A heatwave in the UK is defined by the Met Office as at least three consecutive days with daily maximum temperatures exceeding a county-specific threshold, reflecting a sustained spell of unusually hot weather.

The heatwave threshold temperature varies across the UK. In Greater London it is 28C whereas in Northern Ireland and Scotland it is 25C.

It is likely that a few places could meet the heatwave definition during Friday, Saturday and Sunday. At the moment, areas such as London and the south Midlands are most likely to see this.

With the unseasonable warmth expected to continue into Tuesday and beyond, more parts of England and Wales could experience a heatwave after the bank holiday weekend.

Even in places where a heatwave isn't likely, it still looks warm over the long weekend, with temperatures for most between 20-26C.

As early as Friday afternoon, temperatures are expected to reach up to 28C in south-east England.

This will be the warmest weather of the year so far, exceeding the 26.6C (79.8F) recorded at Kew Gardens in April.

However, there remains uncertainty about how long the warm spell will last.

The most likely scenario is for heatwave conditions to hold on until at least the middle of next week, with a change to something a little cooler and more unsettled from Thursday onward.

Yellow heat health alerts have been issued for five English regions: East Midlands, East of England, London, West Midlands and the South East.

They come into force from 09:00 on Friday 22 March and last until 17:00 on Tuesday 27 May.

Yellow alerts are issued during periods of hot or cold weather that are only likely to affect those who are particularly vulnerable, for example the elderly, or those with existing health conditions.

The main reason for the warmer weather is a change in the wind direction.

The jet stream will shift north this weekend allowing warmer southerly winds to bring hot air from southern Europe and north Africa.

It will feel very different compared to last week when cold winds were blowing from the north.

It is rare to see temperatures up to 30C in the UK during the month of May. The last time this happened was back in 2012 in Scotland.

For England, this potential heatwave could bring the first May 30C since 2005. If we reach 30 Celsius before Monday, this will be the earliest 30C since 1952.

Following downpours for many over the past week, the rain is finally set to ease.

It comes after spring rainfall had been exceptionally low for southern and eastern England up until the start of May. Some places in south-east England have only had around a third of their expected spring rainfall so far.

Wednesday still brings the chance of a few showers, almost anywhere, but they will be less frequent than recent days and temperatures will reach around 21C.

Most parts of England and Wales will stay dry on Thursday and Friday, whilst further showers may affect Scotland and Northern Ireland at times.

Keep up to date with the latest forecast on the BBC Weather app and the Weather for the Week Ahead.