The yellow alert has been issued across East Sussex from Wednesday, with "significant impacts" expected on health services.
A third heatwave of the summer is expected in parts of the UK - as officials warn it is likely to have "significant impacts" on health and social care services.
A yellow heat health alert has been issued for sustained high temperatures across East Sussex from Wednesday at 10am until Tuesday 15th July.
The alert also includes London, the East Midlands, West Midlands, East of England, South East and South West.
"Significant impacts" are likely across health and social care services as the Met Office has predicted heatwave conditions in some areas, with temperatures in the lows 30s centigrade by the end of the week, the alert states.
Two amber heat health alerts were issued in consecutive weeks during two separate heatwaves in June, which provisional Met Office figures suggest will England's warmest on record.
An official heatwave is recorded when areas reach a certain temperature for three consecutive days, with thresholds varying from 25C to 28C (77-82F) in different parts of the UK.
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