UPD:

After about an hour, the situation in north-northeast Attica was extremely difficult, with flooded streets from Peania to Chalandri.

In Agia Paraskevi, a strong hailstorm has broken out resulting in motorists coming to a virtual standstill due to low visibility. This has caused huge traffic jams in main roads in the northern suburbs.

The extreme weather forecast by meteorologists to hit the wider Athens area has already started in the western suburbs with the district of Petroupoli already feeling its effects with heavy rains.

The phenomena will be locally intense, with topical hail storms during the afternoon, according to meteorological service of the National Observatory of Athens.

The main feature of the weather will be electrical activity, which is expected to increase, causing many lightning storms.

In general, heavy rains are expected to hit locally with storms expected to occur in the continental parts of the country, mainly during the afternoon and evening hours.
Isolated storms in the islands of the North and East Aegean are also a possibility. The phenomena will be accompanied by hailstorms, locally intense, while in the areas affected by the storms, there will be gusty winds.