After a humid Friday night, Mr Dewhurst said Saturday would be a case of “role reversal”.
The highest temperatures will be in the east, with a maximum of 34C possible in an area covering London and up towards Lincolnshire.
“We will see the hottest day of the year so far,” said Mr Dewhurst.
He said the spike in UK temperatures was not a heatwave, which are typically considered to last three days or more.
“It’s more just a hot spell rather than a heat wave,” he said.
“It’s different for Europe because it’s more prolonged.”
More widely across the east of England on Saturday temperatures will range between 29 and 32C, while in the west it will be 22 to 25C.
On Saturday night, there will be a risk of thundery showers in northern parts of the UK, bringing fresher air on Sunday.
Maximum temperatures could reach 25C on Sunday in the south east.
Mr Dewhurst said the outlook for next week was a mix of sunny spells, scattered showers and lower temperatures.
Feeling hot, hot, hot: Temperatures set to soar above 30C in UK as Europe continues to swelter – ITV News