Britain is braced for a "Spanish Plume" weather event this weekend which could cause severe storms, flash flooding and even tornadoes.
Hot and humid air is expected to be pushed into northern Europe, creating the phenomenon, forecasters said.
It comes after US scientists found that July was the warmest month on record worldwide and 2015 is likely to be the hottest year.
As the wind becomes southerly on Friday and Saturday, a brief surge of heat from the continent will affect central and eastern parts of England.
Heavy rain is likely to become widespread through the weekend, especially in the west and north. Severe thunderstorms may affect some areas, MeteoGroup said.
The regions most likely to see fairly hot weather include London, which could see temperatures of around 30C (86F) on Saturday, Norwich and Cambridge at 28C (82.4F), and Bath, Birmingham and Lincoln at 25C (77F) or 26C (78.8F).
However, it looks like a slow-moving frontal system will affect western parts of Britain, with heavy rain developing through the course of Saturday.
The heat and humidity in central and eastern areas could trigger severe thunderstorms, especially for the Midlands and northern England. Hail and strong wind gusts are possible.
The rain and areas of thunderstorms then look like spreading into Scotland overnight and into Sunday, with further rain or showers still possible further south. Northern Ireland may escape much of this activity. The unsettled conditions could last into the start of next week, before turning cooler again.
Officials at the National Oceanic and Atmospheric Administration in Washington DC said July's average global temperature was 16.5C (61.86F), beating a previous record set in 1998 and 2010.
The first seven months of this year were the hottest January-to-July span on record.
:: A Spanish Plume is a colloquial description of a weather situation in which a large southwards dip in the high altitude jet stream develops to the west of Europe, encouraging a deep southerly wind flow. This pushes hot and humid air from Iberia north and north-east into northern Europe, including the British Isles.
The proximity of active weather systems moving with the jet stream along with heat from the summer sunshine can encourage thunderstorms. The strong winds from the jet stream help to organise the thunderstorms and can increase their severity.
Forecasters said the Spanish Plume can create a risk of tornadoes, although there is a low risk of that this weekend.