ATHENS, GREECE — Meteorologists are warning of a high probability of a tropical-like cyclone forming in the Ionian Sea to the southwest of the Greek mainland, as gale-force winds continued to batter the country and forced the closure of most schools.

Ferries remained in port Thursday, severing islands’ connection to the mainland. Trees have fallen on power lines in the capital’s northern suburbs, 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.

Meteorologists have warned of the formation of a Mediterranean cyclone, known as a medicane, which combines the words Mediterranean and hurricane, in the Ionian Friday.