According to the Department of Meteorology, the affected regions include the Western, Sabaragamuwa, Southern, Eastern, North-Western, Northern, and North-Central provinces, as well as Monaragala district.
The heat index representing how hot it feels on the human body when relative humidity is combined with air temperature is forecast to rise in parts of these areas.
Officials warned that prolonged exposure to the sun and engaging in outdoor activities may lead to fatigue, while continued exertion could result in heat cramps.
Residents are advised to stay well-hydrated and limit strenuous outdoor activities during peak heat hours.
