The Hellenic National Meteorological Service (EMY) issued an emergency bulletin warning of the sudden onset of a storm front from Tuesday.
The wet spell will bring heavy rainfall, thunderstorms, hail and powerful winds in some places.
The islands of the Ionian and the southern Peloponnese will be affected late Tuesday, followed by the rest of the Peloponnese peninsula, Crete and parts of the mainland including Attica and Evia on Wednesday.
The wet weather will spread to Thessaly, the islands of the Sporades, parts of Epirus and the Cyclades islands on Wednesday, before shifting to the Dodecanese and the islands of the northeastern Aegean.
The stormy weather is expected to ease off on Thursday.
EMY urges citizens and visitors to follow authorities’ instructions and avoid risks.