Greece's national meteorological service has issued red-level storm warnings for Athens and large swaths of the country as Storm Erminio is set to bear down on Wednesday, with forecasters warning of up to 90 millimeters of rain in the greater Athens area and a serious risk of urban flooding across a city of five million people.
The Hellenic National Meteorological Service issued an emergency severe weather bulletin placing Attica, eastern Peloponnese, central Greece, Euboea, Thessaly, the Sporades and the Dodecanese under red alert for Wednesday, with the heaviest rainfall expected from late morning through the evening.
The Ionian Islands, northern Cyclades and Eastern Aegean islands were placed under orange alert.
Meteorologist Tasos Arniakos warned that the most intense conditions would strike western and southwestern parts of the country, the Thermaic Gulf area and Thessaly, with thunderstorms carrying lightning and possible hail.
He urged both authorities and the public to monitor drainage systems, culverts and water runoff points, predicting an improvement from Saturday onward.
For Athens specifically, forecaster Giannis Kallianos compiled projections from thirteen major global weather models, which showed maximum 24-hour rainfall estimates ranging from 60 to 150 millimeters, with an indicative average of around 80 millimeters.
Mr. Kallianos noted that a catastrophic January 2026 storm over Attica had recorded 174 millimeters at Papagos station, killing one woman, offering a benchmark for what the drainage-strained capital could face.
Alpha television meteorologist Giorgos Tsatrafyllias forecast up to 90 millimeters for Attica, stressing that total accumulation was secondary to rainfall intensity.
"If part of that rain falls within a short period at rates of 20 to 40 millimeters per hour or higher, the risk of urban flooding, stream overflow and road network disruption rises sharply," Mr. Tsatrafyllias said.
Red warnings extend into Thursday for western and southern Peloponnese and western Crete.