The National Meteorological Service (EMY) on Monday issued an emergency bulletin warning of the sudden onset of a storm front from Tuesday, interrupting the unseasonably fair weather of recent days.
The wet spell is to sweep into the country this evening from the west and southwest, bringing heavy rain, storms and hail in places.
The islands of the Ionian and the southern Peloponnese are to be affected late Tuesday, followed by the rest of the Peloponnese peninsula, Crete and parts of the mainland including Attica and Evia on Wednesday.
Later on Wednesday, the wet weather is forecast to spread to Thessaly, the islands of the Sporades, parts of Epirus and the Cyclades islands before shifting to the Dodecanese and the islands of the northeastern Aegean.
On Wednesday night, the stormy weather is expected to hit Macedonia and Thrace before easing off on Thursday.