India Southwest Monsoon 2026 – State-by-State Onset Dates & Forecast

The southwest monsoon is the lifeblood of India's agriculture, delivering roughly 70% of annual rainfall between June and September. In 2026 the season comes with a critical split: an early onset on one hand, and a below-normal seasonal rainfall forecast on the other — driven by a developing El Niño. Here is what IMD's official forecasts say and what to expect state by state.

How Monsoon Onset Works

The India Meteorological Department (IMD) declares monsoon onset over a region when specific criteria are met simultaneously: at least 60% of available stations in a region report rainfall of 2.5 mm or more for two consecutive days, alongside supporting atmospheric indicators — deepening of the westerly jet, strengthening of the cross-equatorial flow, and negative OLR anomalies over the region.

Onset is not simply the first rain of the season. A prolonged dry spell after initial rains causes IMD to suspend the onset declaration — as happened in Kerala in 2023. Critically, an early onset does not guarantee good seasonal rainfall totals — the months that follow depend far more on ENSO state and monsoon break/active cycles than on the onset date itself.

Monsoon Progression: Normal Climatology vs. 2026

The chart below shows the normal northward progression of the monsoon from Kerala to northwest India. In 2026 the entire advance is running approximately 4–5 days ahead of normal in the initial phase, consistent with the early Kerala onset. However, as El Niño strengthens through July–August, the advance may stall or weaken over northwest India.

State-by-State Onset Date Table – 2026

Normal onset dates are IMD climatology (1961–2020). The 2026 onset estimates follow from the early Kerala onset (26 May, IMD official), applying typical propagation lead times. The seasonal rainfall signal is based on IMD's April 2026 Long-Range Forecast — onset timing and seasonal rainfall are separate forecasts.

State / Region	Normal Onset	±1 SD Range	2026 Onset Estimate	Onset Signal	Season Rainfall
Kerala	1 Jun	25 May–8 Jun	22–30 May 2026	Early (IMD: 26 May)	Below Normal
Coastal Karnataka / Goa	5–7 Jun	30 May–14 Jun	1–5 Jun 2026	Early (~4 days)	Below Normal
Tamil Nadu	1 Jun	25 May–10 Jun	26–31 May 2026	Early	Near Normal*
Andhra Pradesh	12 Jun	5–20 Jun	7–11 Jun 2026	Early (~4 days)	Below Normal
Telangana	12 Jun	5–20 Jun	7–12 Jun 2026	Early	Below Normal
Maharashtra (Konkan)	10 Jun	3–18 Jun	5–9 Jun 2026	Early (~4 days)	Below Normal
Maharashtra (Vidarbha)	15 Jun	10–22 Jun	10–14 Jun 2026	Early (~4 days)	Below Normal
Odisha	15 Jun	8–22 Jun	10–14 Jun 2026	Early (~4 days)	Below Normal
Chhattisgarh / MP (E)	15 Jun	10–22 Jun	10–14 Jun 2026	Early	Below Normal
West Bengal / Jharkhand	8–10 Jun	2–18 Jun	4–8 Jun 2026	Early (~4 days)	Near Normal*
Bihar	15 Jun	8–24 Jun	10–14 Jun 2026	Early	Below Normal
Uttar Pradesh (E)	18 Jun	10–28 Jun	13–17 Jun 2026	Early (~4 days)	Below Normal
Delhi NCR / UP (W)	27 Jun	18 Jun–10 Jul	22–27 Jun 2026	Slightly Early	Below Normal
Madhya Pradesh (W)	20 Jun	12 Jun–3 Jul	15–20 Jun 2026	Early	Below Normal
Gujarat	20 Jun	12 Jun–2 Jul	15–20 Jun 2026	Early	Below Normal
Rajasthan (E)	1 Jul	22 Jun–12 Jul	26 Jun–3 Jul 2026	Near Normal	Below Normal
Punjab / Haryana	5–8 Jul	26 Jun–18 Jul	3–9 Jul 2026	Near Normal	Below Normal
Himachal Pradesh	27 Jun	18 Jun–10 Jul	23–29 Jun 2026	Near Normal	Near Normal*
Uttarakhand	20–25 Jun	12 Jun–5 Jul	17–23 Jun 2026	Slightly Early	Near Normal*
Rajasthan (W) — Full India	15 Jul	5–25 Jul	12–18 Jul 2026	Near Normal	Below Normal

* IMD indicates near-normal rainfall likely over parts of Northeast India, extreme Northwest, and northern South Peninsular India. Sources: IMD Long-Range Forecast April 2026; IMD monsoon onset bulletin May 2026. Onset estimates for states other than Kerala are derived from typical propagation rates; verify against latest IMD bulletins.

What is Driving the 2026 Monsoon?

El Niño / La Niña (ENSO) — The Dominant Signal

Weak La Niña conditions that prevailed in early 2026 initially provided some support. However, by May 2026 conditions have shifted dramatically — El Niño is now rapidly developing, with NOAA and IRI both assigning a 98% probability of El Niño during May–July 2026, strengthening further through the monsoon season. El Niño conditions are expected to persist through Northern Hemisphere winter 2026–27.

El Niño suppresses the Indian monsoon by weakening the Walker Circulation, reducing moisture flux from the Arabian Sea and Bay of Bengal, and promoting more frequent monsoon break conditions. IMD's below-normal forecast of 92% LPA directly reflects this El Niño signal. Historical El Niño years have included major droughts (2002, 2009, 2014, 2023).

Indian Ocean Dipole (IOD) — Partial Late-Season Offset

The IOD is currently neutral over the Indian Ocean. IMD's model forecasts indicate a positive IOD developing towards the end of the monsoon season (September–October). A positive IOD (warmer western Indian Ocean) can enhance rainfall, but its influence typically comes too late to offset El Niño suppression during the core June–August monsoon months. It may support a better September for parts of south India.

Madden-Julian Oscillation (MJO) — Triggered Early Onset

The MJO played a key role in the unusually early 2026 onset. A low-pressure area formed over the southwest Bay of Bengal around 12–13 May 2026, strengthening cross-equatorial flow and pushing the monsoon into the Andaman Sea by 15–17 May — ahead of the normal 20 May date. This MJO-enhanced convection pulse is what drove the early Kerala onset signal. However, MJO influence is cyclical (30–60 days); subsequent phases will determine active and break spells within the season.

How to Track Monsoon 2026 on VayuMet

1. Enable the Rainfall layer on the main map and step through GFS forecast hours to watch moisture advancing northward. Compare successive 6-hourly runs — if consecutive runs agree, confidence in placement is higher.
2. Check the Seasonal Forecast panel (right panel → Seasonal Forecast → Precip) for CFSv2 district-level anomaly maps. In a below-normal year like 2026, most districts will show negative anomaly (blue tones = below average).
3. Watch the 850 hPa Wind layer — the southwesterly low-level jet (LLJ) over the Arabian Sea strengthening to >15 m/s is the key precursor before each active monsoon spell. During monsoon breaks, this jet weakens and shifts northward.
4. Monitor air quality (GEFS-Aerosols layer) — a sharp drop in dust AOD over northwestern India marks the boundary between dry continental air and advancing monsoon moisture. In El Niño years, this boundary often retreats southward during prolonged break periods.
5. Compare Day 1–2 vs Day 5–7 GFS rainfall — in an El Niño year, GFS often shows active spells at Day 1–2 that evaporate by Day 5 as the monsoon trough weakens. Short-range forecasts are more reliable than extended range in such years.

Historical Kerala Onset Extremes

Category	Year	Onset Date	Days vs Normal	Season Outcome
Earliest on record	1918	11 May	−21 days	—
Recent early onset	2017	30 May	−2 days	Near normal season
2026 (IMD forecast)	2026	26 May	−5 days	Below normal (92% LPA)
Normal onset	—	1 June	—	—
Early onset, drought year	2002	29 May	−3 days	Severe drought (El Niño)
Recent late onset	2019	8 June	+7 days	Near normal season
Latest on record	1972	18 June	+17 days	Drought year

Note: 2002 is included to illustrate that an early onset does not prevent drought when El Niño suppresses mid-season activity — directly relevant to 2026. Source: IMD monsoon onset records.

Further Reading & Sources

• IMD Official Seasonal Forecast Page
• IMD Monsoon Information & Onset Bulletins
• IRI ENSO Forecast (Columbia University)
• NOAA CPC ENSO Diagnostic Discussion
• IITM Pune – Monsoon Research
• How the GFS Model Forecasts Rainfall in India – VayuMet
• Kerala Weather Forecast – VayuMet

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