April max ‘above normal’ but 40°C crossed just once

NEW DELHI: April recorded only one day when the day temperature surpassed the 40-degree mark but the month has not quite been cooler than usual, with the maximum temperature — when averaged over the month — settling half a degree higher than the long period average (LPA) for the 30 days at 37°C.

The assessment is based on data from the India Meteorological Department, which also showed that the last time there was only one day of 40°C in April was in 2020. This year, Safdarjung, the base station for the city, recorded 40.5°C on April 26.

The Met department said that though the number of 40.C°-plus days was kept in check by frequent western disturbances impacting the city, these spells however did not bring significant rain, which would have otherwise led to more perceptible cooling. The LPA for April is 36.5°C.

“April normally averages around four to five western disturbances and we have already seen five. However, none of them have been strong enough to bring moderate to heavy rain, which can keep the temperature down for several days. Most of the rainfall received in April this year has been towards late evening or at night, which does not impact the maximum temperature significantly,” said Kuldeep Srivastava, scientist at IMD.

Till April 29, Delhi had recorded 7.5mm of rainfall, meaning it is likely to end the month in a rain deficit, similar to March. The LPA for April rain is 16.3mm, while it is 17.4mm in March. Delhi only received 4.3mm of rainfall in March, making it a deficit of 75%, IMD data showed. The monthly rainfall was 20.1mm last April and the average monthly maximum was 35.3°C.

That the city could have been cooler had the western disturbances brought more rain is best supported by comparing it with 2020, when there was only one 40°C-plus April day like this year. That year, the average peak for the month was 35.3°C.

Last April, Delhi recorded four days of 40°C or higher and in 2022, there were 16 such days in the month. In 2021 and 2019, Delhi had eight such days each, five in 2018 and 10 in 2017. In 2012, the daytime temperature did not surpass the 40-degree mark in Delhi, and the highest maximum was capped at 38.7°C.

Srivastava said though the western disturbances were feeble and unable to bring much rain, they have kept wind speeds around 20-30 km/hour on nearly 15 days this month — a factor which has largely prevented mercury from rising rapidly during the day.

“Even when we have had clear skies, calm winds have been missing, which can cause temperature to rise fairly quickly. These strong surface winds have kept temperature fairly constant, between 37 to 39°C,” said Srivastava, adding that a dip in temperature by 3-4°C is expected once again in the coming days.

“It could drop to 36°C by Wednesday due to strong winds,” he added.

IMD’s forecasts show a western disturbance could influence parts of Delhi NCR in the early hours of Tuesday, which might bring a drizzle in isolated parts. The next western disturbance, around May 4, is also expected to be weak.

The passing western disturbances, though feeble, are expected to bring strong surface winds with high speed, which would continue to keep the maximum from crossing over the 40°C threshold.

On Monday, Delhi’s maximum was 38.3°C — a degree below normal. It was 38.2°C on Sunday and 38°C on Saturday. Data from previous years showed the highest maximum in April has gone as high as 43.5°C in the absence of rain or strong winds. This was recorded on both April 29 and 30, 2022. Last year, the highest maximum was 40.6°C (April 18). In 2021, it was 42.2 (April 29). In 2020, it was 40.1 (April 16) and 42.1°C in 2019 (April 26).

Though the days have been warmer than usual, the nights have been cooler. The average monthly minimum temperature has been 20.6°C — 0.7 degrees lower than the LPA. It was 19.3°C last April when Delhi received 20.1mm of rainfall. In 2022, it was 22.2°C, when only 0.3mm was received during the entire month.

Mahesh Palawat, vice president at Skymet, a private weather forecaster, said the premonsoon months of April and May generally receive only one or two spells of intense rain, but this has largely been missing in Delhi this year. “We have not seen a good spell lasting two to three days, where the temperature has stayed below normal and there is significant cloudiness. We can expect the temperature to begin to heat up in Delhi only from the second week of May when clear skies return for a prolonged period,” he added.