Tropical nights used to be a rare phenomenon, but they have blighted some Britons struggling to sleep in the heat repeatedly this summer.
The Met Office is now warning the unusually hot nights could continue for a few more days - and will become more frequent in the future - meaning anyone hoping for some respite may be disappointed.
Climate change will lead to more heatwaves in the coming years, as well as more "tropical nights" where after-dark temperatures do not fall below 20C (68F), the forecaster said.
Spokesperson Grahame Madge said tropical nights are "still extremely rare events in the UK, but with a changing climate we can expect to see more incidents".
It follows a State Of The Climate report which found the past decade was the hottest for the world in records dating back to the Industrial Revolution, according to The American Meteorological Society.
While areas of Scotland have been hit by torrential downpours in recent days, large parts of England and Wales have been struck by scorching mid-summer evenings.
The mercury has not fallen below 20C (68F) for four nights in a row, leaving many on social media complaining about it being "impossible to sleep".
While temperatures are expected to dip slightly almost everywhere across the UK over the next few days with thunderstorm warnings and floods predicted in some areas, overnight temperatures are expected to remain high.
A Met Office spokesperson told Sky News that on Wednesday and Thursday nights, some southern areas will still "remain around 20 degrees" and be "uncomfortable for some".
The highest night-time temperature recorded so far this year was 22.3C (72.14F) in Langdon Bay, Kent, they added.
Image:No cool respite in the evenings is a problem for those with long-term health problems and the elderly
There were 44 tropical nights between 1961 and 1990, which were mostly associated with the heatwaves in 1976 and 1983.
Since 1991, there have been 84 tropical nights recorded with around a quarter of these occurring since 2008.
Tropical nights have mostly been confined to the south of the UK, with only three registered in Scotland since 1961 and none in Northern Ireland over the same period.
So far the areas that have seen the highest number of tropical nights this year are Hastings in East Sussex with three, followed by two in Gosport, Hampshire; Heathrow; London City and Wych Cross, East Sussex.
"However, as well as increasing frequency of events we can also expect to see more occurrences outsides of the South East of England," Mr Madge said.
Another Met Office spokesperson, Nicola Maxey, said an increase in warm nights could become a health issue "because if you have a hot day and cool night, then people who have long-term health problems and the elderly have a chance to cool down.
"But if it's constant and you don't have that respite, it becomes more of an issue."
The hot weather will continue for many in the southern half of the UK towards the end of the week, with temperatures expected to hit 34C (93.2F) in some areas on Thursday.
Earlier on Wednesday, the Met Office said temperatures had reached 34.6C (94.28F) in central London, marking the first time since at least 1961 that there have been six consecutive days of 34C and above.