The UKHSA have issued a yellow heat health alert for Essex and the wider East of England from 9:00am on May 22 until 5:00pm on May 27.
The alert signals a higher risk of impacts on vulnerable people, including increased demand on healthcare services and a greater danger to life.
Indoor environments may also become uncomfortably warm for prolonged periods.
This comes as Essex has been forecast a period of high temperatures towards the end of the week.
Daytime temperatures in Essex are forecast to rise from the high teens into the mid-20s in the coming days, with some areas possibly reaching 27C on Friday.
Forecasters, the Met Office have previously said the chances of a heatwave hitting the county have risen.
A spokesman said: “There is an increasing chance of heatwave thresholds being met across parts of England and Wales from Sunday onward.
“On Monday, heatwave thresholds could be met across a wider area, including central southern England and perhaps parts of southwest England and east Wales.
“It will likely remain very warm in any event, with fine weather expected to continue into next week.”
Chelmsford and Colchester are expected to record the highest temperatures in the county, with readings between 24C and 26C.
Coastal locations such as Southend and Westcliff are forecast to remain slightly cooler, hovering in the low 20s.