Two of them lost their lives Tuesday evening in Istanbul, the country’s largest city, where streets were transformed into torrents.
Twelve people were injured, according to a report released by the governor’s office.
Turkish emergency services also deplored three dead and three missing in the province of Kirklareli, in the northwest of the country.
The overnight storm partially flooded a metro station in Istanbul and forced the evacuation of dozens of people from a municipal library, according to press reports.
Images broadcast on television and social media showed floods sweeping away cars and market stalls.
The rains follow a particularly dry summer that saw water reservoirs in this city of 16 million fall to their lowest levels in nine years.