Bengaluru on course for its wettest May ever

Torrential rain that lashed Bengaluru on Tuesday night set some records and may well break more.

In the 24-hour period ending 8:30 am on Wednesday, Bengaluru city received 114.6 mm of rainfall, the HAL airport 86.4 mm, Kempegowda International Airport 66.8 mm and GKVK (Jakkur) 130 mm, data from the India Meteorological Department (IMD) shows.

It was the highest rainfall that the IMD’s city observatory has recorded in a 24-hour period since August 2017. At 253.9 mm of rainfall, this May has turned out to be the wettest for the city since 2012. And if the forecast is anything to go by, it could turn out to be the wettest May ever. The record for the wettest May belongs to 1957 when the city received 287.1 mm of rain. In all, the city observatory has recorded 405 mm of rain this summer (since March 1), an increase of 289 mm.

For HAL airport, this is the wettest May. It received 377 mm of rain this summer, an increase of 269 mm. The figure for KIA is 325 mm.

The rain was so intense that many parts of the city received 10 cm or more of rainfall in just one and a half hours — between 8.15 pm and 9.45 pm.

A Prasad, Scientist-D, Meteorological Centre, IMD, Bengaluru, said Cyclone Asani was not the cause for the rain.

It’s because of two systems in the atmosphere. The first is a north-south trough (an elongated area of relatively low atmospheric pressure) running from eastern Madhya Pradesh to South Interior Karnataka via Vidarbha, Telangana and Marathwada. Running at 0.9 km above mean sea level, it is leading to the convergence of air, which then causes clouds to form and rains to occur, Prasad explained.

The second system, he went on, is a deep upper air cyclonic circulation moving at between 1.5 km and 5.8 km above mean sea level over North Interior Tamil Nadu, Kerala and South Interior Karnataka. “Because of these two systems, we expect rainfall in the next five days,” Prasad said. “Clouds either don’t move or move very slowly, leading to torrential rain.”

The IMD has forecast a generally cloudy sky with a few spells of rain/thundershowers for the city until the morning of May 20 but has issued only a yellow alert, meaning there will be heavy rainfall.

It has forecast widespread rain for coastal and South Interior Karnataka.

Bright day, wet night

Wondering why Bengaluru’s weather is fluctuating, like sunshine during the day and downpour at night? That’s because of the convective rainfall, which occurs via heat transfer by the movement of air molecules. “The sunshine provides energy for clouds to develop. If there is no sunshine, thunderstorms will not occur at all,” Prasad said.