The met office on Saturday afternoon issued an orange warning of high temperatures on Sunday.
Temperatures are expected to reach 43 degrees Celsius inland, 34C in the mountains, 32C on the west coast and around 34C in the other coastal areas.
The warning covers Sunday 1pm to 5pm.
Authorities also issued a red alert on Saturday over the severe risk of forest fires due to high temperatures.
The forestry department said that there was high risk of forest fires and raised the alert level to red. It called on the public to avoid any activity that could cause fire.
A gradual drop could occur on Monday and Tuesday.
The forestry department urged members of the public to immediately call 1407 or 112 (Fire Service) if they see smoke or fire.