Even as October draws to a close, Mumbai continues to wake up to unexpected downpours, long after the official withdrawal of the southwest monsoon. Confused citizens have flooded social media with questions, wondering why the skies refuse to clear. mid-day asked India Meteorological Department’s (IMD) Scientist-B, Nitha Sashidharan, to decode the weather mystery.
Why is Mumbai still experiencing rainfall after October 10, even though the southwest monsoon was officially withdrawn on that date?
The present rainfall activity over Mumbai is associated with a depression over the east-central Arabian Sea and the resulting moisture incursion into the region. Rainfall can occur due to different weather systems, and in this case, no mixed activity has been observed. Two separate systems are responsible for the rainfall in Mumbai — one during the monsoon season (until October 10) and another post-monsoon system (continuing till Sunday). After October 10, when the IMD declared the withdrawal of the southwest monsoon from Mumbai, the city remained largely dry until October 16.
What are the main reasons for Mumbai’s heavy rainfall this week?
Thundershowers with short intense spells were experienced over Mumbai and adjoining areas during past 2-3 days. IMD’s daily forecast has placed Mumbai under a yellow alert, predicting up to 60 mm of rainfall per hour, accompanied by thundershowers. Thundershowers cause short, intense spells of rain, as witnessed on Sunday, unlike the monsoon’s more persistent, day-long showers.
Which factors determine IMD’s announcements for the onset and withdrawal of the monsoon?
For the withdrawal of monsoon, factors like cessation of rainfall activity over the area, establishment of anticyclone in the lower troposphere and considerable reduction in moisture content are considered.
What systems and infrastructure does IMD use to predict weather and issue early warnings?
IMD bases its forecasts on several inputs: synoptic weather observations, upper-air readings, satellite and radar imagery, and numerical weather models.
Regarding early warnings, the department has been closely monitoring the evolution of the current low-pressure system over the Arabian Sea and has been issuing district-wise warnings for the past five days.
