Mumbai: The city this year experienced its driest June in seven years. The India Meteorological Department’s (IMD) base weather station at Santacruz recorded just 252.4mm of rainfall since June 1, as of 8.30am on Wednesday, as against the normal measure of 493.1mm.
This is the lowest June rainfall received in Mumbai since 2014, which happened to be a drought year for the entire country when the IMD received just 87.3mm of rain.
Experts and officials attributed this year’s sluggish monsoon performance to largely three factors. One, lack of low-pressure zones in the Bay of Bengal combined with a ‘weak’ offshore trough in the Arabian Sea, close to the Konkan coast. When the offshore trough is strong, the moisture content in the atmosphere increases, resulting in more cloud cover and rainfall. Strong low-pressure systems in the Bay of Bengal then ‘pull’ this moisture from the sea and deposit it over the Konkan region, and play an important role in maintaining the strength of offshore troughs.
These low-pressure systems did not form because meteorological conditions over the Bay of Bengal were not favourable. Tropical intraseasonal oscillations, including the Madden-Julian Oscillation (MJO) and the Boreal Summer Intraseasonal Oscillation (BSISO), which modulate the formation of these low-pressure systems were not active over the Bay of Bengal, impeding rains not only in Mumbai but across the state of Maharashtra.
Moreover, on June 22, an east-west wind shear zone developed over the south Konkan region, moving north-westward toward south Gujarat. This system prevented rain-bearing clouds in the Arabian Sea from entering inland despite a cyclonic circulation which later strengthened into a low-pressure area close to the Konkan coast. “This caused heavy rains in parts of the south Konkan, but not over Mumbai and adjacent districts,” said Mahesh Palawat, vice-president (meteorology and climate change) at Skymet Weather, a private forecaster.
Thirdly, experts pointed out, that the monsoon low-level jet (MLLJ) which plays a vital role in transporting moisture from the Indian Ocean toward the west coast, kept skipping the Indian subcontinent due to an active Southern Hemisphere Equatorial Trough (SHET) and a disturbance in the Eastern Indian Ocean, which deflected the MLLJ axis and hampered the arrival of moist winds in the north Konkan region.
Weather models are presently showing the formation of the season’s first tropical storm over the South China Sea around July 4, which may then traverse Indo-China passing over Thailand, Vietnam, Laos, and Myanmar before entering the northeast Bay of Bengal around July 6-7. “This storm could turn into the season’s first low-pressure area over the Bay of Bengal, bringing the first monsoon surge to the west coast,” said Abizer Kachawala, an independent weather forecaster.
Experts and officials, however, expressed uncertainty over this outcome. “There is still a possibility of an error with this forecast because it is around a week away. A low-pressure will likely form around July 7, but we are not yet sure how this will impact rains on the west coast,” said an official with the IMD’s regional forecasting centre in Mumbai. This view was echoed by independent meteorologist Akshay Deoras, who said, “Extended forecasts are not showing good rain possibilities after around July 10. Things will become much clearer in the next week. It is a waiting game as of now.”
BOX:
June rainfall in Mumbai:
2022: 252.4mm (up to 8:30am, June 29)
2021: 961.4mm
2020: 395.0
2019: 515.1
2018: 792.5
2017: 523.3
2016: 697.4
2015: 1106.7
2014: 87.3