Rain hope blowin' in the wind

TT, May 9: Gusts of wind brought relief from the sweltering heat today but no shower.

Thunderclouds sailed past the city in the afternoon and the wind picked up around 3.30pm, bringing down the temperature but dashing hopes of squall and rain.

The Met office has held out hope for rain tomorrow.

Calcuttans woke up to a hot and humid morning and the maximum temperature crept up to 36.1 degrees Celsius, a notch above normal. According to weather portal AccuWeather.com, the RealFeel - the impact of heat and humidity on your skin - touched 50 degrees Celsius.

But as the storm approached, clouds filled the sky and blocked out the sun.

The thunderclouds that had formed over Burdwan floated west to east, passing just north of Calcutta. The weather office said the prevailing wind conditions at that time led the clouds towards Rajarhat, Dum Dum and nearby areas and only the outer reaches of the clouds - 12km to 15km tall - passed through the city proper. Not high enough for a squall.

Cumulonimbus clouds carry an updraft and a downdraft of winds at great speeds. A squall happens when tall clouds pass over a particular area because the downdraft escapes from the base of the cloud and reaches the surface.

"At 12-15km above the surface, winds were blowing in the westerly (west to east) direction. For a squall to come to Calcutta, the wind needs to flow in the north-westerly (north-west to south east) direction. It skirted just north of the city," said Sanjib Bandyopadhyay, deputy director general, India Meteorological Department, Calcutta.

The weather office held out some hope of rain on Wednesday, citing a cyclonic circulation over the sub-Himalayan region in Bengal and Sikkim, another cyclonic circulation over Bihar and east Uttar Pradesh and a trough of low pressure from Bihar to south Chhattisgarh across Jharkhand.

"All these systems are pulling moisture from the Bay of Bengal towards themselves. The conditions would thus be favourable for generation of thunderclouds tomorrow as well," Bandyopadhyay said.