A preliminary analysis indicates that on Monday, Mumbai was still under the influence of the clockwise winds or an anticyclone that has been persisting over the Arabian Sea for almost two months now

Massive dust storm along with rains at Vashi area in Navi Mumbai on Monday. (HT Photo)

This week Mumbai was at the receiving end of an unexpected mix of a blinding dust storm, battering winds and sheets of rain but which also dissipated quickly. Freak weather events can always occur because of a confluence of circulation features.

A preliminary analysis indicates that on Monday, Mumbai was still under the influence of the clockwise winds or an anticyclone that has been persisting over the Arabian Sea for almost two months now. These winds tend to bring humidity from the warming Arabian Sea or dust from the Arabian Peninsula and Pakistan depending on exactly where the anticyclone is situated over the sea on any given day. On Monday, it was close to the northern edge of the Arabian Sea and it ramped up the humidity and particulate matter since the morning.

By the afternoon, as the Indian subcontinent warmed up like a popcorn kettle under the scorching sun, the Western Ghats around Nashik managed to fire up a convection cell like kernels of corn popping in the hot kettle. While Nashik itself did not receive any rain, the surrounding Ghats saw heavy rain. The heating due to condensation of moisture began to demand more and more moisture from the Arabian Sea and it also started to sweep in the dust. This created the meld of a dust storm at one end and heavy rain on the other with accelerating winds and rains feeding off each other.

South-westward drift of the rain system

Since the winds were anticlockwise, they began to extend the rain bands from the Ghats down south-westward towards Mumbai. The combination of the dust-loading acting as additional heat pump or cloud condensation nuclei, and the warm, humid air cascading down the Ghats to the coast, likely added to the ferocity of the winds and the rain.

Details are yet to emerge in terms of the processes and the location of the maximum rain – whether it was on the Western Ghats or over the city itself.

Weather station data indicates that Mulund received over 75mm of rain while Powai received only about 34mm. Many parts of Mumbai saw much less rain or even no rain at all. The question then is whether this was just a freak event, or is this part of a weather change that is an emerging pattern.

Middle East warming and Mumbai’s changing weather

I am part of a group that is conducting a series of studies which have been pointing out that the rapid warming over the Middle East or West Asia has been pulling the southwesterly winds over the Arabian Sea northward of its usual location. And this northward pull and the wind shift occurs in March-April-May. The wind shift is causing the warming of the northern Arabian Sea at a fast pace.

The dust storm of January 2022 that covered large parts of Mumbai, Western Ghats and Pune, is still fresh in people’s minds. Monday’s dust storm produced another flavour of the interactions between the Middle East warming, Arabian Sea winds, a dust storm, gusts of wind and sudden pre-monsoon rains over Mumbai. The warming Arabian Sea also contributed to last year’s October heat and is likely to do so again this year.

Change is blowin’ in the wind

It can be expected that the Middle East warming will continue, and it will continue to influence the winds over the Arabian Sea during the pre-monsoon as well as during the monsoon and the post-monsoon. The impact of the Arabian Sea warming and the northward shift of the southwesterly winds are now being manifest as increased instances of extreme rainfall events over northwest India and Pakistan.

Pakistan has seen a large-scale flood every year since 2010. Northwest India too is facing erratic pre-monsoon activities and crop damages as well as heavy monsoon rains. While the climatic impacts cannot be controlled, predicting them well and issuing reliable early warnings is our best strategy.

Given that this phenomenon will continue or even worsen the heat and rainfall extremes over northern Western Ghats and northwest India, adaptions to better manage agriculture, water, energy, health, and such are critical. As for Mumbai, mitigating urban heat island effects with green cover and anti-flooding measures should take top priority.