A weak low pressure system is affecting the area, the met office said in its early morning news bulletin, adding that there will be dust in the atmosphere.
Friday will be mainly fine with increased cloud at intervals. Temperatures will be 29 C inland, 25 C on the south and east coasts, 24 C on the other coasts and 20 C in the mountains.
Increased cloud is forecast for tonight. Temperatures will drop to 15 C inland, 14 C on the coasts and 9 C in the mountains.
On Saturday, Sunday and Monday there will be intervals of mainly fine weather and intervals of increased higher cloud.
Temperatures will edge up to a little above average for the time of year.