"Synoptic Weather Systems Behind Intense Mumbai Rains"

Context:

Mumbai has witnessed extremely heavy rainfall (200 mm+ in 24 hours at some stations) between August 16–19, due to combined synoptic weather systems amplifying the southwest monsoon.

Synoptic systems:

Synoptic systems are large-scale weather phenomena that influence rainfall patterns during the monsoon season in India. They are the immediate drivers of daily and seasonal rainfall distribution.
These includes
- Low-Pressure Systems
  - Types: Depressions, cyclonic circulations, low-pressure areas.
  - Origin: Mostly over the Bay of Bengal (less frequent over the Arabian Sea).
  - Role: They travel inland, carrying moisture and triggering widespread rainfall across central and north India.
  - Depressions: The most important rain-bearing system; responsible for major share of monsoon rains.
- Monsoon Trough
  - An elongated low-pressure zone extending from northwest India to the Bay of Bengal.
  - It oscillates north-south during the season.
  - Northward shift ? heavy rains over Himalayas & NE India.
  - Southward shift ? heavy rains over Gangetic plains, Central & Peninsular India.
  - Break monsoon condition linked to weakening of this trough.
- Troughs & Cyclonic Vortices
  - East–West Troughs: Promote sustained cloud formation & prolonged rain.
  - Cyclonic Vortices: Small-scale circular systems, short-lived but can cause localised intense rainfall.
- Off-shore Trough
  - Runs parallel to the West Coast of India during active monsoon phases.
  - Responsible for heavy rains along Konkan, Goa, Karnataka, and Kerala coast.
- Western Disturbances (WDs)
  - Extra-tropical weather systems originating in the Mediterranean region.
  - Move eastwards and cause rainfall in NW India during winter & early monsoon season.
  - In summer, they interact with monsoon currents, influencing rainfall variability.
- Easterly Waves
  - Formed in the Bay of Bengal and move westwards.
  - Influence east coast rainfall during monsoon and Tamil Nadu rainfall in NE monsoon season.