Weak low pressure is affecting the area and there will be dust in the atmosphere at intervals, the met office said in its early morning weather forecast.
Increased cloud on Thursday is expected to lead to scattered showers while after midday isolated thunderstorms are possible, mainly in the mountains and inland.
Temperatures will be 29 C inland, around 26 C on the south and east coasts, around 24 on the west and north coasts and 20 C in the mountains.
Tonight will be mainly fine but with increased cloud locally, especially in the north. Temperatures will be 12 C inland and on the west and north coasts, 14 C on the south and east coasts and 9 C in the mountains.
On Friday, increased cloud is expected to lead to isolated showers and/or thunderstorms.
On Saturday there will be intervals of increased cloud. On Sunday intervals increased cloud may lead to scattered showers.
Temperatures will edge up on Saturday remaining at the same levels on Sunday.