Seasonal low pressure is affecting the area the Met Office said in its early morning bulletin adding that Thursday will be mainly fine with increased cloud at intervals, mainly in the west and in the mountains.
Temperatures will be 39 C inland, around 32 C on the coasts and around 31 C in the mountains.
Tonight will be mainly fine with the possibility of patchy fog and low cloud. Temperatures will fall to 22 C inland and the south and east coasts, around 20 C on the remaining coasts and 19 C in the mountains.
Friday, Saturday and Sunday will be mainly fine with increased cloud at intervals locally, mainly in the west and in the mountains. Patchy fog and light cloud is forecast at night and early in the morning.
Temperatures are expected to remain at the same levels on Friday, which are about average for the time of year, edging up on Saturday and remaining at a little above average for the time of year on Sunday.