Moody monsoon keeps Mumbai guessing

Hindustan Times

4 days ago

MUMBAI: Mumbai woke up to a fairly sunny August day on Tuesday, not a monsoon cloud in sight. But quirky weather doesn't surprise Mumbaiites any longer. Who would have thought May would steal the monsoon's thunder? (HT Photo)
Experts say the pivotal factor that shapes the Mumbai monsoon, notorious for bringing the city to its knees at least once during its four-month run, are low pressure systems over the Bay of Bengal, which push westerly winds from east to west, and bring moisture, and thus rain, to Mumbai.
The unusual activity, or lack of it, was a curtain-raiser for the strange twists May had in store. What is usually one of two hottest months of the year turned out to be the wettest in over a century – Colaba recorded 503.2 mm of rain and Santacruz 378.4 mm, values not exceeded since 1918.
May also heralded the earliest-ever monsoon onset in recorded history, from the 1950s. Starting May 26, Mumbai saw 135.4 mm rainfall in Colaba and 33.5 mm in Santacruz – embarrassing the BMC for its lack of monsoon preparedness, although some might say it gave them a convenient excuse!
An official with the Indian Meteorological Department (IMD), Mumbai, explains, 'The system over the Bay of Bengal had formed and had a strong pull, which led to a rapid progression from Kerala to Maharashtra. After the pull relaxed, rainfall petered out and took a break.'
It explains the monsoon's slow start in June. But, by mid-month, the rains rolled in like clockwork, delighting Mumbaiites and making sure June hit its usual quota – 500mm-plus for both Colaba and Santacruz. It was a fairly typical month.
Naturally, Mumbaiites braced for a wet July, which usually delivers the season's heaviest downpours. But the skies did not oblige. The rain picked up only during the last ten days, delivering only half the month's average rainfall, at 381.0mm in Colaba and 797.3mm in Santacruz. It was the driest July Mumbai has seen in a decade.
Five days into August and the monsoon's taken a pause – again. Weather experts say that with North India experiencing heavy rain, the region over Mumbai is in an inactive phase. 'As August proceeds, the monsoon will pick up but mainly in interior parts. Expect a slight increase in rainfall over the Konkan and the ghats in Maharashtra between August 12 and 18,' said the IMD official.
What about Mumbai, which by now should have had social media on fire with a deluge of monsoon-related memes and complaints. 'August is also expected to be on the drier side for Mumbai and the whole of Maharashtra,' said an official with the IMD, Mumbai. 'Cloudy skies, especially in the latter half of the day, are on the cards for the next few days. Light rain and thunderstorm activity may be seen starting August 7.'
If the Mumbai monsoon is to meet its 'above normal' seasonal forecast, September will have to deliver. For now, though, the IMD's forecast is not promising. 'As of now, the system in the Indian Ocean Dipole is not favorable for heavy rainfall in September. If those systems change, we could see more active rainfall in the last monsoon month to meet the seasonal forecast,' said an IMD official.
The relatively dry monsoon, at least until now, has not impacted the lakes that supply Mumbai its drinking water. 'The lakes are already 90% full, and some have even overflowed. But the levels will have to hold steady in October to make sure there's enough supply for the year,' says weather enthusiast Rajesh Kapadia.
Of Mumbai's moody monsoon, KS Hosalikar, former head of IMD, Pune, says, 'The beauty of Mumbai's rainfall is that there is a lot of intrinsic intra- and inter-seasonal variability, making it very hard to predict.'
He adds, 'Part of the reason is that Mumbai is surrounded on three sides by water, with moisture always available, so slight changes in the weather system can affect rainfall.'
Hosalikar explains, 'Mumbai's rainfall is full of anomalies and irregularities, all while being normal for Mumbai. The typical pattern of rainfall in Mumbai is that a large chunk is covered by a few heavy rainfall days, while an approximate 20% is covered by light and moderate rain.'