Temperatures are set to reach 25C in parts of the UK on Monday, but the Met Office has said conditions will not meet the official definition of a heatwave.
According to the latest maps from the forecaster, London is expected to reach 25C on Monday, while Manchester and Cardiff could hit 22C and parts of Scotland may see temperatures of 20C.
Heatwave definition and regional thresholds
Despite the warmer weather, temperatures are not expected to reach heatwave levels. The Met Office defines a heatwave as at least three consecutive days where the daily maximum temperature reaches or exceeds a specific threshold for the area. In London, that threshold is 28C, while in Scotland it is 25C.
The Met Office's forecast for Monday to Wednesday warns of rain in some parts of the country, although there will also be spells of "drier and brighter weather".
It said: "Changeable over the next few days with spells of rain and showers, interspersed with some drier and brighter weather. Warm at first, but turning fresher from Tuesday. Breezy at times."
Outlook for the rest of September
Looking further ahead, the unsettled conditions are expected to continue for much of the rest of the month, with showers and strong winds particularly affecting northern and western parts of the UK.
Temperatures are likely to remain close to the September average of 17C, although some warmer days could still develop in the coming weeks.
The Met Office's forecast for September 17 to 26 says: "Remaining changeable, with occasional rain or showers arriving from the North Atlantic, most frequent across northern and western parts of the UK, where some strong winds will also be possible at times.
"However, there will also be some reasonably dry and more settled periods interspersed, especially across southern areas."
"Temperatures for the period as a whole will probably be close to average overall, but there is scope for some rather warm days at times, along with occasional relatively cool nights giving the occasional grass frost."
Flood concerns on the coast
Despite the sunny weather forecast, there is concern for flooding. The greatest of this is along the North Sea coast in and around Hornsea, East Yorkshire. There is also concern for parts of the east coast in Norfolk, particularly at East Cley to Kelling Hard, including Salthouse.
