Delhi's Primary Weather Station Sees No Heat Wave In Pre-Monsoon Season, First Time Since 2014

May is usually the hottest month in Delhi with a mean maximum temperature of 39.5 degrees Celsius, but saw below-normal temperatures and excess rain this time.

New Delhi: Delhi's primary weather station, the Safdarjung Observatory, has not recorded any heat wave in the pre-monsoon season for the first time since 2014, officials said on Tuesday. A few isolated areas, however, witnessed heatwave conditions for a brief period in April and May, they said. May, historically the hottest month in Delhi with a mean maximum temperature of 39.5 degrees Celsius, has recorded below-normal temperatures and excess rain this time. Meteorologists attributed the phenomenon to higher-than-usual western disturbances -- weather systems that originate in the Mediterranean region and bring unseasonal rainfall to northwest India -- this pre-monsoon season (March to May).

"Usually, five to six western disturbances are recorded in the northern plains in April and May. We saw 10 western disturbances, mostly strong ones, this time," said Kuldeep Srivastava, head of the Regional Forecasting Centre of the India Meteorological Department (IMD).

Delhi recorded maximum temperatures above the 40-degree mark for just nine days in May with heatwave conditions affecting some parts for two days.

According to IMD data, the Safdarjung Observatory has so far recorded 86.7 mm of rainfall in May. On average, the national capital logs 19.7 mm of rainfall in the whole month.

The city logged more than 20 mm of rainfall in April, the highest in the month since 2017, and heatwave conditions at isolated pockets.

Overall, Delhi has gauged 158 per cent higher rainfall -- 161.2 mm against a normal of 62.6 mm -- during the pre-monsoon period this year.

"The Safdarjung Observatory, which is representative of Delhi, has not recorded any heat wave in the pre-monsoon season this year. This has happened for the first time since 2014," Srivastava said.

The weather station recorded 13 heatwave days in the pre-monsoon season last year -- nine in April and four in May. It saw just one heatwave day during this period in 2021, four in 2020 and one in 2019.

The threshold for a heat wave is met when the maximum temperature of a station reaches at least 40 degrees Celsius in the plains, 37 degrees in the coastal areas, and 30 degrees in the hilly regions, and the departure from normal is at least 4.5 degrees.

Rain, thunderstorm hit Delhi; 10 flights diverted

A severe thunderstorm reaching speeds up to 80 kilometres per hour and rain hit the national capital on Tuesday evening, affecting vehicular movement and leading to the diversion of many flights. The IMD said another western disturbance is likely to bring storms and rain to the northern plains, including Delhi, over the next few days. Maximum temperatures are predicted to remain below the 40-degree mark until June 5.

The Safdarjung Observatory on Tuesday recorded a maximum temperature of 35.9 degrees Celsius, five notches below normal.

Delhi experienced moderate to severe thunderstorms with lightning and gusty winds, reaching speed of 70-80 kilometres per hour, the Met office said.

As gusty winds blew across the city, many pedestrians rushed for shelter as it began to rain while vehicular traffic was also affected.

"Due to bad weather in Delhi, 10 Delhi-bound flights were diverted (nine from Jaipur and one from Lucknow) between 6:25 pm and 8 pm," an airport official said.

The weather office has issued a 'yellow' alert for Wednesday, warning of traffic disruptions and inundation of low-lying areas due to rain. The maximum temperature is expected to hover around 35 degrees Celsius.

With the IMD anticipating a slight delay in the arrival of the southwest monsoon, the maximum temperatures are likely to remain above normal for a longer-than-usual period in June.

"During June, normal to above-normal maximum temperatures are likely across most parts of the country, except for the extreme north and some parts of the southern peninsular region," the IMD said.