The Met Office has issued a yellow alert for Friday, saying local heavy thunderstorms are likely, with precipitation exceeding 35 mm per hour.
The yellow alert is in force from 11 am to 6 pm.
It said that Friday will start off with intervals of mainly fine weather and local increased cloud coverage which on the coast will lead to local showers and thunderstorms.
Gradually, clouds will gather that are expected to lead to local showers or isolated thunderstorms which may be heavy and accompanied by hail and strong winds.
Temperatures will be 21 C inland and on the east coast, 22 C on the remaining coasts and around 11 C in the mountains.
Local showers and isolated thunderstorms are also expected in the evening, mainly close to the coast.
Saturday will be partly cloudy and cloudy at intervals, with local rain and isolated thunderstorms. Temperatures will remain at about average for the time of year.
Sunday and Monday will see intervals of mainly fine weather with clouds at intervals. Local showers are possible on Monday evening.