A lightning strike captured over the CSMT railway station in Mumbai.
(Shriram Vernekar/TOI, BCCL, Mumbai)
Friday, October 8: Over the course of this week, the story of Mumbai’s weather has remained more or less the same: typically warm October mornings and afternoons, followed by evenings filled with the rumbling of clouds, flashes of lightning and blasts of thunder!
These spine-chilling evening thunderstorms, and the intensity at which they have occurred all week, has taken the City of Dreams by storm. And they may very well continue, with forecasts indicating the prevalence of such conditions at least for the next one week.
To know more about these thunderstorms and understand why Mumbai is experiencing these dramatic conditions, The Weather Channel India got in touch with Sridhar Balasubramanian, an Associate Professor at IIT-Bombay and a weather expert.
We asked him some FAQs related to this phenomenon, the answers to which are listed below:
Firstly, how do these thunderstorms form?
Thunderstorms are usually an evening feature. Two major factors are essential for their formation: high daytime temperatures (which cause vigorous instability in the atmosphere); followed by the incursion of moisture from the seas/oceans (usually facilitated by sea breeze or the presence of a cyclonic circulation in the sea).
Due to the high daytime temperature, the warm air has a tendency to hold more moisture and rise to very high levels vertically. This is why we see very tall cumulonimbus clouds during thunderstorms.
As warm air rises, it condenses; and as it keeps rising, it freezes into ice. The instability in the atmosphere (triggered by high daytime temperatures) causes a vigorous collision of these ice particles, giving rise to thunder and lightning.
Once the clouds become big enough, they precipitate, causing thunderstorms.
Why are these thunderstorms occurring in Mumbai?
Warm daytime temperatures triggered by a weak anti-cyclone and warm winds blowing from land to sea are the main factors contributing to the occurrence of thunderstorms in Mumbai. The latter is expected, considering the monsoon is currently displaying signs of withdrawal.
Furthermore, a cyclonic circulation that is currently located in the Arabian Sea is incurring tremendous amounts of moisture, effectively fuelling these thunderstorms.
Are these thunderstorms an unusual occurrence for Mumbai?
No, they are very common during October, when the monsoon gets ready to withdraw. The wind pattern starts changing, causing high daytime temperatures. Then by evening, a monsoon circulation system brings moisture inland, resulting in such thunderstorms.
However, what’s unusual is the intensity of the thunderstorms. Such strength and intensity is usually seen in the interior regions, and not in the coastal zones. But with climate change, the temperatures are soaring higher during daytime, thereby allowing such intense thunderclouds to form.
For how long are these conditions likely to prevail in Mumbai?
Mumbai could see these thunderstorms up until October 14-15, depending on how high the daytime temperatures get and how much moisture is dragged inland due to prevailing monsoon systems, mainly from the Arabian Sea.
It may not be a daily feature, but until October 14-15, such activity shouldn’t come as a surprise considering the meteorological factors will remain conducive.
For more insights, follow Professor Sridhar on Twitter.
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