The region is under pressure from the El Nino weather phenomenon, with the volume of rainfall in the northern Amazon below the historical average.
All districts have been experiencing heat that is two to five degrees above normal over the past week.
The 2003 heatwave, which saw temperatures in Europe reach 47.5 degrees Celsius, was one of the worst natural disasters of recent decades.
Weather office says all districts likely to experience temperatures 3-4 degrees Celsius above normal
The Kerala State Disaster Management Authority (KSDMA) has issued cautionary instructions for the public in view of the increasing temperatures.
The Ballia Chief Medical Officer has, however, claimed that only two died of heat stroke, other fatalities were related to fever and other diseases.
A yellow alert has been declared in Ernakulam and Idukki districts on Wednesday. The districts may receive 64.5 mm to 115.5 mm rainfall in the next 24 hours.
IMD sounds yellow alert in Idukki for Sunday.
Summer showers have somewhat reduced the extreme heat conditions in Palakkad, Thrissur and Kozhikode districts.
Palakkad district recorded the highest maximum temperature of 38.4 degrees Celsius