Calcutta received only two Nor'westers instead of the seven or eight it normally gets by now, making this May - traditionally the wettest month of the season - uncomfortably hot.

Nor'westers are strong thunderstorms generated in the Chhotanagpur Plateau and are characterised by tall, dark clouds that travel north-west towards Calcutta, bringing soothing showers and strong winds. These storms that blow across the city bring down the temperature and suck out moisture from the air making the evening pleasant after a hot and humid summer day.

"Normally, the period between March 15 and June 15 is known as the period of Nor'westers. The number of storms keeps increasing as the summer progresses. There are about eight to nine Nor'Westers every season. But this year it has been unusually dry," said a senior official of the Ranchi Met office.

With Nor'westers staying away, the heat generated during the day is not being able to escape at night and the city has felt like a pressure cooker. "With the moisture in the air not being able to escape, the relative humidity remained very high. So people felt extremely uneasy throughout the day in the sun and even at night," said G.C. Debnath, director, India Meteorological Department, Calcutta.

As a result, the RealFeel, according to Accuweather.com , hovered between 48 and 53 degrees Celsius on most May afternoons and the minimum temperatures shot above 30 degrees Celsius for the first time in over a year.

On April 28, the season's first Nor'wester brought 33.6mm of rain to Calcutta, the highest of the month, and winds blew at 52kmph. The May 3 Nor'wester brought 23.5mm of rain and winds raged at 44kmph.

According to weather scientists, there needs to be both heat and humidity in the Chhotanagpur Plateau for the generation of Nor'westers. This time, the humidity was missing. "There needs to be a confluence of two types of winds, the hot and dry winds from central India and moist winds from the Bay of Bengal for the generation of Nor'westers," said a weather scientist.

Calcutta did receive three other squalls in the season - where wind speeds exceeding 43kmph were sustained for over a minute - but some of them brought as little as 1mm of rain.

On Wednesday, the maximum temperature in the city jumped a notch to reach 37.4 degrees Celsius and the RealFeel hovered between 45 and 48 degrees Celsius. With no rain still on the radar the uncomfortable weather in Calcutta is likely to continue for the time being before the pre-monsoon showers arrive, not before the start of next week at the earliest.