A warm air mass is affecting the area and there will be dust in the atmosphere until Friday, the met office said in its early morning bulletin.
Thursday will see intervals of mainly fine weather as well as intervals of high cloud. Temperatures will rise to 40 C inland, 34 C on the north and east coasts and 32 C on the remaining coasts and in the mountains.
These temperatures are some 5 C higher than average for the time of year and prompted the met office to issue an extreme high temperature warning effective from 2 pm to 430 pm.
Tonight will see intervals of increased higher cloud and there may be light fog or low cloud at dawn tomorrow. Temperatures will fall to 22 C inland, the north coasts and mountains and around 23 C on the remaining coasts.
Friday will be mainly fine with intervals of increased cloud. Temperatures will edge down in some areas, except in the mountains where no significant change is expected, but remaining noticeably higher than average for the time of year.
Over the weekend, the weather will be mainly fine. Temperatures will drop noticeably on Saturday, remaining above average for the time of year, edging down further on Sunday to close to average for the time of year.