The Meteorological Department has warned that thunderstorms and 60mph thunderstorms are going on in Britain for nine hours today.
Forecasters have urged Britons to stay safe during the “high” with “dangerous” winds and heavy rain that could lead to travel chaos.
Delays in road, rail, air and ferry transport are “likely”, while power cuts and loss of other services are possible.
It comes as the Met Office has placed the southeast of England under a yellow weather warning.
Wind and rain warnings are in place from 1 pm tonight to 10 pm, during which strong southerly winds will blow across Britain.
Wind gusts are expected to reach 50-50mph inland – while the coast could be battered with thunderstorms as strong as 65mph.
Meanwhile, parts of South England will receive 30-40 mm of rain in 3-6 hours.
Alex Deakin of the Met Office said: “The first weekend of October and it will be very autumn.
“There will be some strong winds, particularly in the south on Saturday and north on Sunday, as well as some heavy rain.
“It won’t rain all weekend, but especially in the south later on Saturday, it’s looking really humid.
“Then on Sunday, it will be a little brighter. Some sunshine for most, but still lots of foggy showers.”
It could get so cold in the coming weeks that parts of the UK could see snow.
Experts predict that there is a possibility of some snowfall in the higher regions in the second half of October.
“We are likely to see some snowy weather in the higher parts as October approaches November,” Greg Duhurst, senior meteorologist at the Met Office, told Online.
“The likely areas to be affected are the Scottish Mountains as well as the highlands in northern England and northern Wales.
“Low areas are unlikely to see any. It’s fairly normal for this time of year.”
With only the first day of the month, the chances of this month going down as the hottest October on record have dropped to 5/1.
Jessica O’Reilly of Ladbrokes said: “October got off to a bad start and we’re forced to lower the odds this month, it’s a record breaker.”