After brief lull, rains set to return to Mumbai from tomorrow

Despite registering a surplus of over 3,000 per cent in May, IMD data shows that in June, so far, the Colaba coastal observatory has received 83 mm of rain while the Santacruz station has registered 87 mm of rain. This marks a departure of between 23 mm to 26 mm below the normal.

When can Mumbai witness a revival in showers?

As monsoon showers gather pace, the Konkan region, which includes Mumbai, is also set to experience heavy to very heavy rainfall, with isolated pockets of the region even forecast to witness extremely heavy rainfall between Friday and Saturday.

For perspective, rainfall in the range of 64.5 mm to 115.5 mm in a 24-hour period is categorised as ‘heavy rain’, while 115.6 mm to 204.4 mm of rain in the same duration is attributed as ‘very heavy rainfall’. Meanwhile, showers exceeding 204 mm of rain within a 24-hour window are categorised as ‘extremely heavy rainfall’.

Amid the likelihood of rains gathering pace, the weather bureau has issued a yellow alert in Mumbai, Thane and Palghar districts, after Thursday, stating the likelihood of heavy rainfall coupled with thunderstorms and gusty winds. In other districts of Konkan, which include Raigad, Ratnagiri and Sindhudurg, an orange alert has been sounded between Thursday and Saturday.

What is influencing this resurgence?

Meteorologists have attributed the incoming spell of heavy rains to developing systems such as a trough and an upper air cyclonic circulation over north Odisha. For the record, a monsoon trough is an elongated low-pressure area which extends from the heat low over Pakistan to the Bay of Bengal. It is a semi-permanent feature of monsoon circulation, and its southward movement results in heavy downpours. Meanwhile, a cyclonic circulation is an atmospheric wind flow in upper levels associated with any low-pressure system.

For Mumbai, systems such as troughs and low-pressure systems are crucial in ushering in heavy showers during the monsoon.

As of Tuesday, there was a trough which was running from north Tamil Nadu to south Maharashtra coast as a shear zone, which persists approximately 3.1 km and 4.5 km above the mean sea level. Meanwhile, referring to an upper air cyclonic circulation over north Odisha and neighbourhood, the IMD said that the system is likely to move westward over southern parts of Maharashtra.

“Under the influence of the systems, rainfall activity over Maharashtra is likely to increase during the next 12-17, June,” added the IMD.

Interestingly, the revival of showers also coincides with the typical date of monsoon onset in Mumbai, which is June 11.

Why did Mumbai experience a dry spell?

When Mumbai experienced its earliest onset in the past 75 years on June 26, it had been driven by favourable conditions, with a key factor being a low-pressure area along the west coast. However, after ushering in heavy rainfall in the region between May 24 – May 27, the low-pressure area system fizzled out.

Following this, none of the weather systems–they are responsible for heavy showers ranging from strong westerly winds, troughs or the Somali Jet–were active. In the absence of a strong system, the city experienced only passing showers over the past two weeks.

According to IMD scientists, this lull is typical of the southwest monsoon, which is characterised by dry and wet spells, which are phases influenced by the presence of active systems.

With Mumbai now expected to experience a revival in monsoon currents, experts have said that conditions are also favourable for the further advancement of monsoon over parts of central and east India after Saturday.