Calcuttans prayed for a Nor?wester on Sunday as the mercury crossed the 40-degree mark in the afternoon, making it the hottest day of the season.

The maximum temperature recorded at Alipore during the day was 40.6 degrees Celsius, six degrees above normal.

In Dum Dum, the maximum temperature was 40.4 degrees. The hot spell is likely to continue for the next 24 hours.

Officers at the Regional Meteorological Centre in Alipore said the temperature rise was due to a change in the wind-flow pattern.

?Over the past four or five days, the wind direction has changed. Dry and hot winds have been flowing from the north-western parts of the country and the temperature is shooting up. As there is no wind from the south, there is virtually no incursion of moisture from the Bay of Bengal. So, the dry heat is searing us,? an officer said.

Calcutta is yet to weather the first Nor?wester this season. ?By this time, we usually have two to three Nor?westers. But this year, there has been none. Only a Nor?wester can cool down the city. But, we can?t expect any thunderstorm right now as there is little moisture in the atmosphere during the day,? an officer said.

The maximum temperature has been rising steadily over the past four or five days. On Saturday, the maximum temperature stood at 38 degrees at Alipore.

On Sunday, the minimum humidity recorded by the Met office was 21 per cent.