The Department of Meteorology has issued an extreme high temperature warning, valid from 11.30 until 17.00 on Thursday.
In issuing the yellow alert, it said that the maximum temperature inland is expected to rise to around 40 degrees Celsius.
And in its morning weather forecast, the met office said that Thursday will be mainly fine. Increased local cloud around midday may lead to isolated showers, mainly in the mountains. Temperatures will rise to 40C inland, around 36C on the north coast, around 34C on the remaining coasts and around 31C in the higher mountains.
Friday, Saturday and Sunday will be mainly fine. There will be increased low cloud in the early hours of the morning, mainly in the west and north, and patchy fog locally, mainly inland. Temperatures will remain at the same levels until Saturday, edging down slightly on Sunday to remain a little above the seasonal average.