The warning, which has been issued by the UK Health Security Agency, came into play at 12pm and will last for the entire weekend until 6pm on June 22.
It covers the entire South East region, which includes Southampton, the New Forest and surrounding areas.
READ MORE: Hour-by-hour forecast with Southampton set to be as hot as Greece today
The health alert warns that there is likely to be an increase in demand for health services and that internal temperatures in care settings, like hospitals or homes, may exceed the recommended threshold for clinical risk assessment.
The UKHSA said: “Significant impacts are possible across the health and social care services due to the high temperatures, including a rise in deaths, particularly among those aged 65 and over or with health conditions.”
The heat may also affect the ability of workforces to deliver services, with indoor environments overheating increasing the risk to vulnerable people living independently.
Dr Agostinho Sousa, head of extreme events and health protection at UKHSA, said: “Our findings shows that even moderate heat can result in serious health outcomes, especially for older adults, and it is therefore important that everyone takes sensible precautions while enjoying the sun.”
