While nine died in Burdwan district, three each were killed in Kolkata and Purulia district.
In Burdwan district, five died in several parts of Asansole sub-division, its Sub-Divisional Officer Surojit Dutta Sharma said.
Four others died in Durgapur, hospital sources said. The deaths occurred both yesterday and today.
Three persons -- a woman and two men -- died of sunstroke in three different places in Kolkata today, police said.
A 33-year-old man died due to sunstroke at Charah in Purulia district today, District Magistrate Abanindra Singh said, adding that the toll has reached to three persons in the past three days.
The Regional Meteorological Office said Birbhum, Burdwan, Bankura, Purulia and West Midnapore districts recorded around 45 degrees Celsius or more during the day, while Kolkata registered the season's highest of 40.2 degrees Celsius.