The ‘False Monsoon Signal’: Why Early Rain in Mumbai May Mislead Forecast Expectations
The sudden downpours in Mumbai signal the arrival of the monsoon. As winds strengthen and temperatures drop temporarily, rain is all around; however, what we see is actually ‘false monsoon signals’ rather than the true monsoon itself.
What Is a ‘False Monsoon Signal’?
‘False monsoon signal’ refers to pre-monsoon rainfall events that create an illusion of monsoon-like conditions, therefore suggesting the onset of the monsoon. These rains are characterised by being:
* brief,
* concentrated in the location
* caused by thunderstorm activity rather than by monsoon-related wind systems
While they may appear to be monsoonal in nature, they do not behave as monsoonal events do.
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Why Mumbai Gets Early Rain Before the Monsoon
1) Pre-Monsoon Thunderstorms
Due to rising temperatures in May, there is upward movement of air, which meets up with moisture flowing north out of the Arabian Sea and provides the ingredients for the formation of sudden thunderstorms.
These storms have the following three characteristics:
1) intense precipitation, but short-duration,
2) lightning and strong winds, and
3) sharp decline in air temperature.
2) Temporary Moisture Surge
In unusual circumstances (but unfortunately infrequently), moisture may be drawn into Mumbai ahead of schedule by the respective weather/disturbance system; however, there is insufficient development of the monsoon system itself in terms of providing adequate moisture to support sustained precipitation over an extended period of time.
3) Atmospheric Instability, Not Seasonal Shift
The primary difference is that while pre-monsoon rainfall events are manifestations of atmospheric instability, the monsoon is based on an established system and provides continuous rain for an established period of time.
What Real Monsoon Onset Looks Like
The monsoon is defined as having:
- Steady rain that lasts for several days
- Steady wind from the south-west for a prolonged time
- Rain that occurs over a large area (not just small areas or one storm)
- Mumbai usually experiences it in mid-June, not May.
What to Expect in the Coming Weeks
Going by current data expectations:
- Hot, humid weather will continue
- The rain will continue to be scattered and inconsistent
- There will be sudden storms, but not for very long
Final Words
Mumbai’s early rain doesn’t mark a change. It cools down for just a little while, gets your hopes up, then it will be hot & humid again. The monsoon doesn’t arrive sporadically – it comes as a regular, large amount and stays.
FAQs
1. Did Mumbai experience Monsoon earlier than when it is supposed to?
No! Rain we have experienced so far is associated with pre-monsoon activities
2. Why does it appear as though we have a monsoon?
Because thunderstorms made it appear as such temporarily!
3. Will it continue raining daily from here on out?
No. Rain will continue to be sporadic until we actually enter the monsoon.
4. When can we expect actual relief?
When the monsoon comes, it usually comes around mid-June.
