By Wednesday, the autumn chill will be firmly established and it is expected to be the first day since 11 June when temperatures fail to reach 20C anywhere in the UK.
Cooler north-westerly winds will bring sunshine and scattered showers to many areas, while rain could be heavy and persistent for a time across south-eastern England and East Anglia.
Temperatures will fall into the mid-teens across much of England and Wales. Scotland could see highs of just 10-13C.
The wind will also make it feel colder than the thermometer suggests, particularly around eastern coastal areas.
While mid-teen temperatures are perfectly normal for early October, the sharp contrast with the warmth of recent weeks is likely to make the change feel much more dramatic.