Mumbai is currently experiencing pre-monsoon showers, and anticipation is building as weather experts predict the arrival of the southwest monsoon in the city within the next few days. The India Meteorological Department (IMD) has indicated that conditions are favorable for the monsoon to advance into Maharashtra, with some forecasters suggesting an onset around June 5-7, 2025, slightly ahead of the usual date of June 11.

The early arrival of the monsoon in Kerala, which occurred on May 24, 2025, nearly a week ahead of its normal onset date, has further fueled expectations of an early monsoon in Mumbai. The IMD attributes this early arrival to prevailing favorable weather conditions and expects the monsoon to progress steadily towards Maharashtra.

While the typical onset date for Mumbai is around June 10 or 11, the actual arrival date can fluctuate significantly. In recent years, the monsoon has arrived as late as June 25 (in 2019 and 2023) and as early as June 5 (in 2021). This variability is influenced by a range of factors, including the formation of low-pressure areas, the intensity of the summer heat, and the presence of cyclonic systems.

The city has been experiencing unusual pre-monsoon activity, with rainfall totals already approaching levels not seen since the early 2000s. The Colaba and Santacruz observatories have recorded significant rainfall since March 1, with a majority of it occurring in May. This surge in pre-monsoon showers has raised hopes for an early monsoon arrival, with some experts suggesting it could arrive in the first few days of June.

While a precise date is still uncertain, the current conditions suggest that Mumbai is on track for an early monsoon in 2025. The IMD has issued a yellow alert for Mumbai and Thane until May 28, indicating moderate to heavy spells of rainfall with thunderstorms and gusty winds.

Mumbai's Historical Monsoon Onset Dates

While the anticipation for the monsoon's arrival is high, it's interesting to look back at historical data. According to available records, Mumbai has experienced monsoon onset in May only three times in recorded history: in 1872, 1952 and 1956. This makes the possibility of a May onset a rare and noteworthy event.

The average date of monsoon onset over the Mumbai area during the period of 1781–1878 was June 10, with a standard deviation of 6.9 days. However, a study suggests that the climatic regime governing monsoon advance over western India has changed, with monsoon onset occurring at a generally later date since 1955.

Factors Influencing Monsoon Onset

Several factors influence the onset and progression of the monsoon. These include:

• The formation of low-pressure areas: Low-pressure systems in the Arabian Sea and the Bay of Bengal can either accelerate or delay the monsoon's progress.
• The intensity of the summer heat: Early and intense heatwaves can lead to early pre-monsoon showers and potentially an early monsoon onset.
• Cyclonic systems: Cyclones can pull the monsoon trough forward, favoring an early onset, but they can also disrupt the monsoon flow and cause it to stall.

The IMD is closely monitoring the situation and will continue to provide updates as the monsoon approaches. While Mumbaikars eagerly await the arrival of the monsoon, they should also be prepared for the possibility of heavy rainfall, thunderstorms, and gusty winds.