Delhi enjoyed its coolest May in 36 years, says IMD

Delhi was affected by multiple western disturbances over the past month, resulting in the Capital experiencing its coolest May since 1987, with the average maximum temperature for the month settling at 36.8 degrees Celsius (°C) — more than three notches below the long period average (LPA) for May — India Meteorological Department (IMD) data showed.

In 1987, the average maximum temperature for May was 36°C.

A western disturbance refers to an area of “disturbed” or reduced air pressure, moving from the west to the east, carrying with it moisture associated with rainfall, snowfall and fog in northern India, and at least five affected the Capital in May. These weather systems led to gusty winds, overcast skies, and intermittent rain, and brought down the city’s temperature considerably. In fact, the maximum mercury breached the 40-degree mark on only nine occasions this May.

Also Read: Delhi-NCR likely to see more rainfall in next 2 days; IMD issues yellow alert

In comparison, Delhi in May 2022 had an average monthly maximum of 40.1°C, and the maximum temperature breached the 40-degree mark on 19 occasions, while in 2021, the monthly maximum average was 37.5°C, though the day’s high breached the 40-degree mark on only seven occasions.

The gusty winds and rain also led to a marked drop in the minimum temperature, which averaged at 22.2°C — the lowest in 12 years, and 3.6 degrees below the LPA for May, IMD data showed.

Kuldeep Srivastava, scientist at IMD, said, “This May saw the lowest monthly maximum temperature for Delhi since 1987. The average monthly minimum is the lowest in at least 12 years, with minimum data not readily available before 2011.”

Srivastava added, “The month started with two western disturbances in the first and second week, a third in the middle of May, and now two towards the end of the month. Each spell had gusty winds of speeds of around 50 kmph, and even when it did not rain much, we still had overcast conditions for large parts of the day.”

Mahesh Palawat, vice president at Skymet meteorology, a private weather forecaster, said western disturbances are not very common in May, as they tend to shift to higher latitudes by this time of the year. “Northwest India mainly gets impacted by convective rain, which is when local thunderclouds form over an area due to moisture and high temperatures. This time around, we have seen these western disturbances remain at fairly low latitudes and thereby influence northwest India and central India too, bringing rain. This appears to be an exception, as this does not happen every year, nor should it repeat next year,” he said, adding that there are chances of another weather system developing over Delhi-NCR by June 2 and 3.

The IMD currently has a yellow alert in place for Delhi for Thursday, with chances of light rain and gusty winds of up to 50 kmph being expected. The maximum temperature is likely to be around 33°C, while the minimum will be around 21°C.

The Met department data also revealed that this year, the Capital logged its warmest day on May 22, when the mercury touched 43.7°C. However, the city did not record a single heatwave day this month, though isolated parts of Delhi recorded heatwave conditions in brief spells between May 12-16, and later between May 21 and 23.

In comparison, the city recorded four heatwave days in May 2022.

This May, Delhi also recorded fog — something not witnessed in the summer month for several decades — with visibility dropping to 100m at Palam on May 4, which was the Capital’s coldest morning in 41 years day, with a minimum temperature of just 15.8°C. The last time Delhi had recorded a lower minimum at Safdarjung was on May 2, 1982, when it was 15.2°C.

Till last year, the normal monthly mark for rain in May was just 19.7mm, based on the period 1960-2010. From this year onwards, IMD revised the figure to 30.7mm, after rain data between 2010 and 2020 was included — a period in which the city largely saw excess rain in May.

However, in May 2023, even this monthly average was cleared with ease, with the capital recording an overall excess of 262% this year in terms of rain.

Delhi ended the month with 111mm of rainfall, making it the fourth wettest May for Delhi between 1991 and 2023. The city only received more rain in 2002 (129.3mm), 2021 (144.8mm), and 2008 (165mm — the all-time high for May).

1991 is the first year for which IMD has full rain data for May.

Srivastava said that while pre-monsoon showers are common in May, as a combination of high temperature and local moisture can lead to the formation of convective clouds fairly quickly, the intensity of rain this year has been higher, largely influenced by these western disturbances.

“In 2021, Delhi received 119.3mm of rainfall in a single day due to Cyclone Tauktae. This year, the spread of rain has been more widespread and fairly even throughout the month. That has made it even cooler than 2021,” he said.