The Met Office has raised the level of its extreme high temperature warning from yellow to orange.
In a new alert, it warned that the maximum temperature is expected to exceed 42.5 C in many areas of the island.
The warning is in force until 5 pm.
“Be prepared that high temperatures will lead to health risks amongst vulnerable people e.g. the elderly and very young. Listen to and act upon advice from the authorities,” it said.
Yesterday, the Met Office had issued a yellow alert for today.