Waves of heavy rain and dust blown in from North Africa are expected to sweep across Greece starting Friday.
Forecasters warn that storms in the west could turn dangerous.
Low-pressure systems that formed over the Iberian Peninsula are moving east toward Greece, meteorologist Klearchos Marousakis said.
They will hit western regions first before spreading east.
The worst of the weather is expected in the northern Ionian Sea, the northwestern Epirus region and western central Greece.
Heavy rain and locally severe thunderstorms are forecast there. Mr. Marousakis said the storms could reach dangerous intensity from Friday.
Persistent southerly winds are also carrying dust from North Africa across the eastern Mediterranean. The haze is expected to peak Friday and will be heaviest over western Greece, the Cyclades islands and Crete.
Temperatures will stay unusually high for mid-November in many parts of the country, creating unstable conditions.