The city of Catania at the foot of Mount Etna has been particularly hard hit.
A woman is the third fatality counted from the current natural disasters in southern Italy.
Catania - A lot is coming together in Sicily.
The region of Italy is preparing for the second major storm within a week.
The Ispra authority expects the storm with waves more than 4.5 meters high between Thursday evening and Friday morning on the east coast.
At the same time, the Etna volcano erupted again a few days ago.
At its foot, parts of Catania were completely flooded.
Water and mud flowed into a number of houses, and in some cases the power went out.
The city's police have now reported a third fatality from the heavy rain.
A woman, like her husband, probably got out of the car on Sunday and was caught in the water.
Her body was discovered about three miles from the car.
Her husband had previously been found dead about two kilometers away.
Another man died in Catania on Tuesday, who also got out of his car.
"Nightmare": Etna volcano in Sicily active again
Etna, which is more than 3350 meters high, has been very active so far this year.
Since mid-February it broke out regularly and sometimes spectacularly.
The ash raining down is often a problem for people in the area, and Catania airport has also had to temporarily stop operations in the past because the runway was dirty.
The Sicilian government pledged two million euros in aid to the municipalities in September for the ash damage.
The Coldiretti Agricultural Association spoke on Saturday that the "nightmare" was returning to the Sicilian fields.
The ashes cause damage to the cultivated areas.
Standards are needed that protect farmers.
The cleaning of the fields takes time, water and therefore a lot of work at barely affordable costs.
(dpa / frs)