While temperatures in parts of England are set to reach the highly 30s C - and may even peak at 40 degrees C - the Kingdom is likely to see conditions in the mid-20s.
That means it will also avoid the amber warning which has been put in place for parts of Scotland including Lothian and the Borders, and Dumfries and Galloway.
Temperatures of between 22 and 24 C are forecast for across Fife over Saturday and Sunday.
The Met Office says a few scattered showers may also develop late on Saturday.
It will get hotter at the start of next week.
The mercury could rise up to 27 by Tuesday in Kirkcaldy, 29 in Dunfermline and 28 in Glenrothes.
By Wednesday there could be some light rain as the forecast is for 19 degrees C.
A Met Office spokesman said: “A hot spell is likely to develop from Sunday, likely peaking early next week, leading to widespread impacts on people and infrastructure.
"After a very warm night, hot weather, already underway across other parts of England and Wales is expected to develop more widely across Wales, southwest and northern England, plus southern Scotland. Some exceptionally high temperatures are possible, both by day and by night, for Monday and Tuesday. This following a warm weekend, will likely bring widespread impacts to people and infrastructure.”
Th warnings and rising temperatures come a Scottish Water issued an urgent ‘save it’ plea after customers drained public supplies by 200 million litres extra last weekend, mostly through watering their gardens.
Road tankers have been drafted in to begin delivering supplies to parts of the country, such as the isle of Arran, beginning to show the first signs of drought.
And at the same time, the Scottish Environment Protection Agency reports that much of the east of the country is now in ‘moderate scarcity’ for water, the second-highest warning possible.
The seeds of the current water shortage were sewn last year. Scotland’s water authorities warned then that only significant rainfall over autumn and winter would replenish declining water stocks, which never materialised.
Last weekend over just two days, customers used an additional 200 million litres from their taps in their homes and gardens – the equivalent of 100 Olympic-sized swimming pools – as temperatures soared.
Scottish Water also say you should take shorter showers and turn the tap off when brushing your teeth.
There is no prospect yet of a hosepipe ban but Scottish Water said it was ‘closely monitoring’ growing public water consumption, which 'could put pressure' on supplies.
Kes Juskowiak, water operations manager, said: “The warm, dry weather has seen an increase in the amount of water being used by customers and the amount we need to put into the system to meet that demand.
“Continued warm weather, a lack of rainfall and continued high use levels in the home and garden could put pressure on supplies in the days and weeks ahead.
“We are doing all we can to maintain water supply to customers.”