And it has warned that there could be disruption to road and rail journeys, with a risk of localised flooding.
The alert will be in place for 12 hours from 2 pm today (Monday Sept 5).
The weather experts say the thunderstorms are likely to cause disruption during Monday evening and overnight.
The alert warns that driving conditions are likely to be affected by spray, standing water, hail and gusty winds.
Lightning can cause power surges, so it says we should unplug any non-essential appliances if not already using a surge protector.
When you hear thunder you are already within range of where the next ground flash may occur, lightning can strike as far as 10 miles away from the centre of a storm - so if you are in an exposed area, you should get to shelter.
During the thunderstorm
Telephone lines can conduct electricity so try to avoid using the landline, unless in an emergency. If outside avoid water and find a low-lying open place that is a safe distance from trees, poles or metal objects.
Avoid activities such as golf, rod fishing or boating on a lake, the Met Office says.