Temperatures as high as 28 degrees have already been recorded in both counties, with Suffolk predicted to peak at 31.
The hottest temperature recorded in Suffolk so far stands at 28 degrees at Lakenheath, while Stansted in Essex also recorded 28.
Chris Bell, forecaster for Weatherquest, is predicting highs of 30 to 31 degrees as the day goes on.
Wattisham in Suffolk has recorded a temperature of 25 degrees, with a humidity of around 60%.
Mr Bell said: “We are forecasting highs around the 30 degree mark which will be the hottest day of the year so far in Suffolk.
“Humidity yesterday was around 40%, so while we saw temperatures of 27 degrees, it may not have felt as hot.
“Today it will be around 60%, meaning people will really feel the heat.
“We are probably going to have a very sticky night, with temperatures struggling to drop below 20 degrees.
“Friday night will also be uncomfortable.”
Tomorrow, Mr Bell predicted a cooler day, with highs of 27 degrees. He said a cold front coming in from the west would bring clouds with it.
The weather is already delaying trains across the region, click here to find out more
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