Forecasters are warning that a tropical-like cyclone is due to hit Greek islands, bringing gale-force winds and possible landslides.
The storm has been labelled a ‘Medicane’, which combines the words Mediterranean and hurricane.
The poor weather is being caused by an area of low pressure developing in the Mediterranean Sea off the northern coast of Africa.
Heavy rainfall and flash flooding in Tunisia and Libya over the last week have killed at least five people.
The storm is expected to hit islands in the Ionian Sea, to the southwest of the Greek mainland, on Friday.
Sky’s weather producer Joanna Robinson said: “There is some uncertainty on the track of this storm, but parts of southeast Europe and northeast Libya will see damaging winds, dangerous seas and significant rainfall.
“At the moment, southern Greece looks most at risk this weekend, particularly Crete.
“This system is capable of bringing severe gales, along with up to 250mm of rain in 24 hours.”
She added that flash flooding and landslides are possible.
Most schools have already been closed and ferries on some islands have remained in ports, severing their connections to the mainland.
Trees have fallen on power lines in the northern suburbs of Athens, while the fire department said it received more than 350 calls to remove debris.
Authorities in the Saronic municipality near Athens, on the Ionian island of Zakynthos and the Aegean islands of Tinos, Andros and Mykonos ordered schools to remain shut.
The last notable Medicane was back in 2014, bringing gusts of up to 96mph in Malta.