Monsoon breaks the wall: Mumbai gets first rain showers as system moves
Mumbai recorded passing showers across its suburbs on Sunday, June 21, breaking weeks of an unusual dry spell that had pushed the city's reservoirs to critically low levels. Here is the science behind why the monsoon was held back for so long and why the rain is finally here.
Mumbai waited weeks for this.
The city woke up on Sunday, June 21 to passing showers rolling across its suburbs, the first proper rain of the season after an unusually long and punishing dry spell.
Ghatkopar recorded roughly 24 mm, Worli around 25 mm, Lower Parel 21 mm, and Chembur 20 mm, all in the early morning hours.
Residents in Mulund called it the first real rain they had seen all season.
In Thane, people stepped outside just to smell the petrichor, that sharp, earthy scent that wet soil releases after a long dry period.
The India Meteorological Department (IMD) has issued a yellow alert for June 22 and 23, warning of thunderstorms, lightning, and gusty winds reaching 30 to 40 kmph at isolated places.
Conditions are also favourable for the southwest monsoon to advance further into Maharashtra around June 23.
The relief is real. But the science behind why it took this long is even more interesting.
WHY MUMBAI WENT SO LONG WITHOUT RAIN
Mumbai's reservoirs had dropped to roughly 9 to 10 per cent capacity by mid-June.
The city had recorded a rainfall deficit of over 90 per cent in some areas.
The Colaba weather station recorded only about 4.3 mm for the early part of June, a number that tells you everything about how badly the monsoon had stalled.
The scientific reason for this is a process called entrainment.
The clouds that bring Mumbai its heavy monsoon downpours are towering convective systems called cumulonimbus clouds.
They grow when warm, moist air rises rapidly from the ocean surface, cools as it climbs, and condenses into water droplets.
But for weeks, a layer of dry air was sitting at the middle levels of the atmosphere, getting pulled into the base of these rising columns.
Dry air evaporates water droplets faster than they can form.
The clouds collapsed before producing a single drop of rain. That dry air was the wall the monsoon could not break through.
Saturday night, it finally did.
HOW THE WESTERN GHATS ARE HELPING
The showers arriving over Mumbai are partly being driven by storm cells forming over the Western Ghats through a process called orographic lifting.
When strong, moist southwesterly winds blowing off the Arabian Sea strike the steep slopes of the Ghats, the air has nowhere to go but up. As it rises, it expands and cools, and the moisture it carries condenses into thick clouds.
This condensation releases latent heat, the energy stored in water vapour that gets released when vapour turns to liquid, which further powers the upward motion and builds the storm cell.
When upper-level winds push these cells westward toward the coast, they break over Mumbai as the passing showers the city woke up to on Sunday morning.
WHY SOUTH MUMBAI ALWAYS GETS IT FIRST
There is a reason weather observers consistently predict that rain creeps into south Mumbai before anywhere else.
South Mumbai is a narrow peninsula with the open Arabian Sea on three sides.
It is the first landmass in the path of incoming marine moisture.
As onshore winds strengthen and rainbands organise over the water, the tip of the peninsula intercepts them before the rest of the city does. The rain then moves northward into the suburbs and interior Thane.
Heavier and more widespread rainfall is expected to build through the coming week, with significant intensification likely around June 25 and 26 as the monsoon system strengthens further.
The wall is down. The monsoon is moving.
Mumbai waited weeks for this.
The city woke up on Sunday, June 21 to passing showers rolling across its suburbs, the first proper rain of the season after an unusually long and punishing dry spell.
Ghatkopar recorded roughly 24 mm, Worli around 25 mm, Lower Parel 21 mm, and Chembur 20 mm, all in the early morning hours.
Residents in Mulund called it the first real rain they had seen all season.
In Thane, people stepped outside just to smell the petrichor, that sharp, earthy scent that wet soil releases after a long dry period.
The India Meteorological Department (IMD) has issued a yellow alert for June 22 and 23, warning of thunderstorms, lightning, and gusty winds reaching 30 to 40 kmph at isolated places.
Conditions are also favourable for the southwest monsoon to advance further into Maharashtra around June 23.
The relief is real. But the science behind why it took this long is even more interesting.
WHY MUMBAI WENT SO LONG WITHOUT RAIN
Mumbai's reservoirs had dropped to roughly 9 to 10 per cent capacity by mid-June.
The city had recorded a rainfall deficit of over 90 per cent in some areas.
The Colaba weather station recorded only about 4.3 mm for the early part of June, a number that tells you everything about how badly the monsoon had stalled.
The scientific reason for this is a process called entrainment.
The clouds that bring Mumbai its heavy monsoon downpours are towering convective systems called cumulonimbus clouds.
They grow when warm, moist air rises rapidly from the ocean surface, cools as it climbs, and condenses into water droplets.
But for weeks, a layer of dry air was sitting at the middle levels of the atmosphere, getting pulled into the base of these rising columns.
Dry air evaporates water droplets faster than they can form.
The clouds collapsed before producing a single drop of rain. That dry air was the wall the monsoon could not break through.
Saturday night, it finally did.
HOW THE WESTERN GHATS ARE HELPING
The showers arriving over Mumbai are partly being driven by storm cells forming over the Western Ghats through a process called orographic lifting.
When strong, moist southwesterly winds blowing off the Arabian Sea strike the steep slopes of the Ghats, the air has nowhere to go but up. As it rises, it expands and cools, and the moisture it carries condenses into thick clouds.
This condensation releases latent heat, the energy stored in water vapour that gets released when vapour turns to liquid, which further powers the upward motion and builds the storm cell.
When upper-level winds push these cells westward toward the coast, they break over Mumbai as the passing showers the city woke up to on Sunday morning.
WHY SOUTH MUMBAI ALWAYS GETS IT FIRST
There is a reason weather observers consistently predict that rain creeps into south Mumbai before anywhere else.
South Mumbai is a narrow peninsula with the open Arabian Sea on three sides.
It is the first landmass in the path of incoming marine moisture.
As onshore winds strengthen and rainbands organise over the water, the tip of the peninsula intercepts them before the rest of the city does. The rain then moves northward into the suburbs and interior Thane.
Heavier and more widespread rainfall is expected to build through the coming week, with significant intensification likely around June 25 and 26 as the monsoon system strengthens further.
The wall is down. The monsoon is moving.
