Heavy rain is forecast and a thunderstorm warning has been issued – but temperatures could rise above 30C later this week in parts of the UK.
A yellow thunderstorm warning was issued for Northern Ireland for Monday, with 15 to 20mm of rain expected to fall in less than an hour.
Met Office spokesman Stephen Dixon there will be heavy rain overnight, moving from the south of England to the North East.
Southern and western parts of England could see 30mm of rain which would make for “uncomfortable driving conditions”, he added.
Read the weather forecast for your area
Mr Dixon said: “The weekend could get up to the high 20s or low 30s, the South East will see the warmer weather.
“The week will be sitting relatively warmer for this time of year but more subdued than we’ve seen, but areas will hit heatwave criteria as we get to the weekend.”
The hottest temperature of the year so far was 32.2C (89.9F) recorded on June 10 in Surrey, but the forecaster said the weather is not likely to reach that level this week.
As for the rest of the week, Wednesday will be more of a showery day rather than persistent rain, but drier in the South East.
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As of Thursday, there will be some showers but temperatures will start to rise towards the weekend.
One flood warning was in place on Monday for the River Cole at Coleshill, Birmingham, from Cole End to Coleshill Industrial Estate.
A total of six flood alerts have been issued, meaning flooding is possible.
