Weather Decoded: Mumbai's Monsoon – Expect Early Showers & Above-Normal Rain

 The IMD's 2025 Monsoon Outlook indicates that Mumbai and its metropolitan regions are expected to receive above-normal rainfall during the southwest monsoon season (June to September). Quantitatively, for the country as a whole, the monsoon seasonal rainfall is likely to be 105% of the Long Period Average (LPA), with a model error of ±5%. This suggests a generally good monsoon season for Mumbai.

Monsoon Onset:

• There are indications of an earlier onset of the monsoon this year.
• Conditions are currently favourable for the advance of the southwest monsoon into parts of the Andaman Sea, the South Bay of Bengal, and the Andaman and Nicobar Islands around May 13, 2025.
• The monsoon is likely to reach Kerala around May 27th or May 28th, 2025, which is a few days earlier than the typical onset date of June 1st.
• While a specific date for Mumbai's monsoon onset is yet to be announced, an earlier arrival in Kerala often influences the progression towards Mumbai. The IMD will release more specific onset forecasts for Mumbai closer to the date, likely in the last week of May.

Mumbai Monsoon 2025 Forecast: 

+----------------------+ 

| ABOVE NORMAL | <--- (IMD Prediction) 

+----------------------+ 

| Normal (LPA) | 

+----------------------+ 

(Indicates total rainfall expected to be more than the Long Period Average) Nationally: 105% of LPA (±5%)

Pre-Monsoon Activity (Current Situation - Mid-May 2025):

• Mumbai has already been experiencing significant pre-monsoon rainfall activity in May.
• As of early May, the Santacruz observatory had recorded 33.9 mm of rain since March 1st (against an average of 32.5 mm), and the Colaba observatory recorded 48.7 mm (against an average of 46.7 mm). Some reports indicate this has been the wettest May for Mumbai since 2021, with Santacruz recording 34 mm of rain in a short period around May 7th-8th.
• Yellow alerts have been issued by the IMD for Mumbai and neighbouring districts like Thane, Raigad, and Palghar for May 13th and 14th, 2025. These alerts predict thunderstorms accompanied by lightning, light to moderate rainfall, and gusty winds (30-40 kmph) at isolated places.
• This pre-monsoon activity has been attributed to factors like a low-level trough causing wind pattern disruptions and western disturbances.

Southwest Monsoon Onset Progression (2025 Prediction):

 

|-------------------|--------------------|--------------------|-------------------> Towards Mumbai

Early May         Mid-May            Late May            Early June 

                    [ Predicted: May 13 ]

                    Andaman & Nicobar Islands

 

                                             [ Predicted: May 27th/28th ]

                                            Kerala Onset (Earlier than normal)

 

                                                                             [ Typical: June 1st ]

                                                                            Kerala Onset (Normal)

 

                                                                               [ Mumbai Onset: Likely Early - Awaited ]

Conceptual Monthly Rainfall Pattern - Mumbai (Above Normal Monsoon):

 

June     |  ▆▆▆▆▆▆▆

July     |  ▆▆▆▆▆▆▆▆▆▆▆▆▆▆▆  (Peak Month - Higher than average)

August   |  ▆▆▆▆▆▆▆▆▆▆▆▆▆    (Peak Month - Higher than average)

September|  ▆▆▆▆▆▆

 

(**This is a general representation. Actual monthly distribution will vary and specific IMD forecasts will provide details as the season progresses.**)

Pre-Monsoon Activity (Current Situation - Mid-May 2025):

• Mumbai has already been experiencing significant pre-monsoon rainfall activity in May.
• As of early May, the Santacruz observatory had recorded 33.9 mm of rain since March 1st (against an average of 32.5 mm), and the Colaba observatory recorded 48.7 mm (against an average of 46.7 mm). Some reports indicate this has been the wettest May for Mumbai since 2021, with Santacruz recording 34 mm of rain in a short period around May 7th-8th.
• Yellow alerts have been issued by the IMD for Mumbai and neighbouring districts like Thane, Raigad, and Palghar for May 13th and 14th, 2025. These alerts predict thunderstorms accompanied by lightning, light to moderate rainfall, and gusty winds (30-40 kmph) at isolated places.
• This pre-monsoon activity has been attributed to factors like a low-level trough causing wind pattern disruptions and western disturbances.

Expected Rain Patterns During Monsoon Months (June - September):

• While the overall forecast is for an "above-normal" monsoon, the precise distribution and intensity across the individual monsoon months (June, July, August, September) will be detailed in subsequent, more specific forecasts issued by the IMD.
• Traditionally, July and August are the wettest months for Mumbai. With an above-normal prediction, we can anticipate substantial rainfall during these peak months.
• It is important to stay updated with the IMD's local forecasts, as these will provide more granular information on the intensity and distribution of rainfall as the monsoon progresses.

Key Takeaways for Mumbai Residents:

• Be prepared for an active and likely above-average monsoon season.
• Expect the monsoon to arrive possibly a bit earlier than usual.
• The current pre-monsoon showers are a precursor to the main rainy season.
• Stay tuned for regular updates and warnings from the IMD, especially regarding heavy rainfall events, to take necessary precautions.

The IMD will continue to monitor the atmospheric conditions and provide updated forecasts. For the most current and detailed information, please refer to the official IMD website and its Mumbai regional centre updates.