The rare cyclone Ianos 'hit' the islands of Zakynthos, Kefalonia, Ithaca on Thursday evening.
Greece's national meteorological service issued a top level Red Alert for winds, rain and storm conditions.
"We are preparing to face a rare extreme weather phenomenon," Deputy Civil Protection Minister Nikos Hardalias said, adding that citizens living in regions likely to be affected by the weather front should limit their movements to only those that are strictly necessary.
"Mediterranean cyclones are relatively rare phenomena, which we have encountered in Greece since 1995, but they have intensified and become more frequent in the Mediterranean region due to climate change," he added.
The minister also called on the citizens of Achaia, Arcadia, the Argolid, Viotia (Boeotia), Etoloakarnania, Fokida, Attica and Evia, who live in areas that have flooded in the past or are near rivers, streams or shorelines, to avoid going in basements and ground floors for prolonged periods of time.
He also urged them to stay with relatives or friends if possible and avoid crossing rivers or flooded roads "for any reason, either on foot or by vehicle."
'Ianos' according to the forecasts, is expected to intensify during the night.
Professor of Dynamic Tectonic Applied Geology & Natural Disaster Management, Efthymios Lekkkas confirmed while speaking to MEGA, that the powerful weather phenomena is expected for the next 48 hours.
At the same time, he added that heading south is not a favourable development as "if it came to Attica, ie from land areas, the phenomenon would be greatly weakened... When it goes to the southern Peloponnese, I am very afraid that it will be strengthened even more. If it is exactly on the coastline, it is strengthened by the sea mass, and it is discharged intensively in the land area, that is, we will have intense phenomena in Patras, Kyllini, Zacharo, Kyparissia and Methoni.
Meanwhile, the General Secretariat for Civil Protection warned residents about the extreme weather phenomena.
On Friday, Ianos is expected to affect the Peloponnese, central Greece, Attica and Evia. The Cyclades islands are expected to be affected as of Friday night, while on Saturday it is possible that Crete will also be impacted.
According to a study published in 2011, only one or two medicanes (a rare hurricane storm) occur per year. These powerful storms usually happen during the months of September and October, when sea surface temperatures in the Mediterranean are still quite warm, although they can occur at any time of year.
Warmer sea surface temperatures in the Mediterranean can allow the storms to take on more tropical appearances and characteristics, increasing the wind speeds and making the storms more intense.