Temperatures are to reach as high as 29°C in Gainsborough this week - but predictions of a thunderstorm look set to dampen the heat.
The Met Office says there is a 90 per cent probability of heatwave conditions from today till Friday.
However, forecasts have also predicted isolated heavy showers or thunderstorms for Friday, July 27.
Today and tonight:
Highs of 29 °C. Warm and muggy with plenty of clear spells at first. It may become a little cloudier into the early hours but staying dry throughout. Minimum temperature 18 °C.
Highs of 26 °C. A bright and mainly dry day, with some long sunny spells. Isolated heavy showers or thunderstorms could develop in the south into the evening. Maximum temperature 31 °C.
Outlook for Wednesday to Friday:
Mainly dry with bright or sunny spells, but heavy showers or thunderstorms are possible in the afternoon periods. Hot or very hot throughout but fresher towards the coast.
UK Outlook for Friday, July 27, to Sunday, August 5:
From Friday and through the following weekend a west/east split in the weather is expected, with cloudier, windier conditions in the west and northwest with some outbreaks of rain. In the east and southeast there'll still be some fine and sunny conditions, but with a risk of thundery showers moving north. Widely very warm or hot in the south and southeast, with warm and humid nights, whilst western areas may turn cooler. Through the rest of the period there'll be plenty of fine weather, but occasional rain in the west may spread to other parts at times, and there's an ongoing risk of thunderstorms, particularly across central and southeast England. Temperatures generally very warm away from the west, with hot or very hot conditions at times, especially in the southeast.