As of May 26, 2026, formal monsoon onset over Kerala is yet to be declared — but all pre-onset indicators remain broadly favorable. IMD had pointed to May 26–27; should onset slip by a day or two, the atmospheric setup still supports arrival on or around the climatological normal of June 1, possibly a little earlier. What is unambiguous is the season ahead: every major global forecasting agency — IMD, ECMWF, NOAA/CPC, WMO, JMA, and the UK Met Office — has converged on a below-normal monsoon season for India in 2026. The driver is a rapidly developing El Niño, expected to strengthen through the very months India needs its rains most.
🌧 IMD Long Range Forecast — April 13, 2026: Seasonal (JJAS) rainfall for India as a whole is forecast at 92% of the Long Period Average (LPA) — firmly in the Below Normal category. India's first below-normal monsoon forecast since 2023. The MMCFS dynamical model projects El Niño conditions developing during the monsoon season itself.
📋 Seasonal Forecast Disclaimer: All agency outlooks presented here are probabilistic guidance products, not deterministic forecasts. A below-normal central estimate does not mean the entire country will be uniformly dry — spatial distribution, intra-seasonal variability, and active/break cycles can significantly alter outcomes at the regional level. Read the full disclaimer in Section 5.
For IMD to declare monsoon onset over Kerala, three simultaneous criteria must be satisfied: sustained westerly winds at 925 hPa (≥ 15–20 knots), Outgoing Longwave Radiation (OLR) below 200 W/m² over Kerala and Lakshadweep, and rainfall at ≥ 60% of the 14 designated Kerala meteorological stations for two consecutive days. The Andaman & Nicobar Islands received their monsoon onset on May 16 — six days ahead of IMD's own forecast — signalling a highly energetic pre-onset configuration.
| Parameter | Status (May 26) | Assessment |
|---|---|---|
| Low-Level Jet (925 hPa) | 15–22 knots | Favorable |
| Cross-Equatorial Flow | Active | Favorable |
| OLR over Kerala | 185–195 W/m² | Favorable |
| Moisture Flux Convergence | Increasing | Favorable |
| Upper-Level Anticyclone (150 hPa) | Establishing | Marginally Favorable |
| MJO Phase | Phase 2–3 (Maritime Continent) | Marginally Favorable |
| ITCZ Position | 8°N–12°N | Favorable |
The synoptic picture is broadly favorable for onset in the coming days — on or around the climatological normal of June 1, and quite possibly a little ahead of it. The MJO in Phase 2–3 is not actively suppressing convection over the Indian Ocean, and the pre-onset low-pressure system in the southeast Arabian Sea has maintained the deep convection needed to satisfy IMD's threshold criteria. Critically: an early onset does not predict a good season. Onset timing reflects current synoptic energy; the seasonal total reflects the multi-month state of the Pacific and Indian Ocean — and both point clearly below-normal in 2026.
The El Niño-Southern Oscillation (ENSO) cycle is the dominant remote forcing agent of the Indian Summer Monsoon. For 2026, the signal is no longer ambiguous — El Niño is developing with near-consensus agreement among all global modelling centres. ENSO-Neutral conditions prevailed through most of 2025, with a weak La Niña tendency emerging in November–December 2025. However, Niño3.4 SSTs began warming rapidly from February 2026 onward. By May 2026, the trajectory toward El Niño is unmistakable — the equatorial Pacific is crossing the +0.5°C anomaly threshold that formally defines El Niño onset.
| Index / Agency | Status / Probability | Trend |
|---|---|---|
| Niño3.4 SST Anomaly | Approaching +0.5°C threshold | Rising |
| NOAA/CPC El Niño Prob. (May–Jul) | 82% | High |
| IRI/CCSR El Niño Prob. (May–Jul) | 98% | Very High |
| El Niño persistence (Dec 2026–Feb 2027) | 96% (CPC) | Near Certain |
| IOD (Indian Ocean Dipole) | Currently Neutral | Positive IOD expected by September |
| PDO (Pacific Decadal Oscillation) | Mixed | No significant offset provided |
El Niño suppresses the Indian monsoon by warming the central-eastern Pacific, tilting the Walker Circulation, weakening the cross-equatorial low-level jet, and reducing moisture flux into the subcontinent. Historically, El Niño years produce below-normal monsoon rainfall in approximately 60–65% of cases. With El Niño expected to develop during the monsoon season and strengthen through July, August, and September — the most critical months are precisely when the suppressive influence will be most intense.
The Indian Ocean Dipole (IOD) provides a partial offset: IMD and global models forecast a shift from neutral to a positive IOD phase toward the latter half of the monsoon season. A positive IOD enhances moisture inflow from the Arabian Sea and may improve late-season September rainfall across parts of India. The precise regional beneficiary — whether the signal strengthens the peninsula, the northwest, or the Himalayan arc — is model-dependent and will only become clear as the season progresses and forecast lead times shorten. It is a modifying factor, not a corrective one — it cannot rescue the season for central India regardless of where the benefit ultimately concentrates. The magnitude of the developing El Niño remains the single largest source of forecast uncertainty for the season overall.
Every spring, the world's premier climate prediction centres release seasonal outlooks for the upcoming monsoon season — probabilistic assessments expressing the likelihood of rainfall falling in the below-normal, normal, or above-normal tercile over the June–September season. Here is how the major global agencies assess JJAS 2026 for India.
Methodology: Statistical Ensemble Forecast System (SEFS) supplemented by the Monsoon Mission CFS (MMCFS) dynamical model. LRF Stage-1 issued April 13, 2026.
IMD Regional Guidance:
Methodology: NMME (North American Multi-Model Ensemble, 8+ coupled GCMs) + CFSv2 flagship dynamical model. ENSO Assessment: 82% probability of El Niño emerging May–July 2026, rising to 96% through NH Winter 2026–27. The NMME consensus strongly favours El Niño forming by June and persisting through the year.
India Monsoon Signal (JJAS 2026): Below-normal precipitation over most of India's core monsoon zone. The CFSv2 ensemble shows a strong negative precipitation anomaly over central and northwestern India, consistent with established El Niño teleconnection patterns. Northeast India retains a near-normal to mixed signal, partially sheltered via Bay of Bengal moisture pathways.
Methodology: SEAS5, a 51-member ensemble dynamical model — widely regarded as the world's most sophisticated operational seasonal prediction system.
SEAS5 shows a 70% likelihood of below-normal to drought conditions over the South Asian monsoon region for JJAS 2026. The ensemble mean indicates a clear negative precipitation anomaly over central and western India for the full June–September period, deepening from July onward as El Niño strengthens. South Peninsular India may see near-normal to improved rainfall assisted by the late-season positive IOD tendency.
The 34th Session of the South Asian Climate Outlook Forum (SASCOF-34) was convened on April 28, 2026 at Malé, Maldives — bringing together WMO-designated Regional Climate Centres and national meteorological services from across South Asia.
"Below normal rainfall is most likely during the June–September 2026 southwest monsoon season across most parts of South Asia, with the strongest deficit signal over central parts of the region. Parts of the north-western, north-eastern and southern sub-regions are likely to receive normal to above-normal rainfall. There is strong consensus among experts that El Niño conditions are likely to develop during the 2026 monsoon season. The Indian Ocean Dipole is expected to transition from neutral to a positive phase."
— SASCOF-34 Consensus Statement, April 28, 2026
The WMO has separately confirmed in its Global Seasonal Climate Update: "South Asia is expected to receive below average monsoon rainfall" — based on inputs from all WMO-designated climate centres globally, including ECMWF, NCEP, JMA, BoM, Météo-France, and the UK Met Office.
Both the UK Met Office (GloSea6, 42-member ensemble) and JMA (MRI-CPS3, 50-member ensemble) have contributed their outputs to the WMO Global Seasonal Climate Update and SASCOF-34 consensus. Their JJAS 2026 India outlooks:
Specific tercile probability tables from JMA and the UK Met Office are available via their respective operational portals and are best consulted directly for the most current ensemble runs.
| Agency | Model / System | All-India Forecast | Below-Normal Probability | Key Driver |
|---|---|---|---|---|
| IMD | SEFS + MMCFS | 92% LPA — Below Normal | ~60–65% | El Niño developing |
| ECMWF | SEAS5 (51-member) | Below Normal | ~70% | El Niño + SST anomalies |
| NOAA/CPC | NMME + CFSv2 | Below Normal | Consistent negative | El Niño 82% probability |
| WMO / SASCOF-34 | Multi-model consensus | Below Normal (most of S. Asia) | Strong consensus | El Niño developing |
| JMA | MRI-CPS3 (50-member) | Below Normal | Aligned with WMO | El Niño + IOD |
| UK Met Office | GloSea6 (42-member) | Below Normal | Aligned with WMO | El Niño |
Cross-Model Consensus: All six major seasonal forecasting centres independently point to a below-normal monsoon for India in 2026. The convergence across independent models with different physics and SST initialisation provides strong confidence in the below-normal outcome as the central scenario. The principal unknowns are the depth of the deficit — dependent on El Niño's final intensity — and the spatial distribution of the worst shortfalls.
VayuMet Weather has analysed NOAA CFSv2 dynamical model output (30-member ensemble, initialised May 25, 2026) for the June–September season. The CFSv2 signal reflects the developing El Niño pattern: a suppressed monsoon trough across central and northwest India, with the northeast showing mixed behaviour driven by Bay of Bengal moisture pathways, and September carrying the highest forecast uncertainty of the four months.
The CFSv2 ensemble's most consistent and severe signal covers the northwest-to-central belt. These are deficits sustained month by month — not a brief break in the monsoon. This is a drought signal. The classic El Niño imprint — a weakened, southward-displaced monsoon trough — is clearly expressed in this corridor. Madhya Pradesh (−75.3%) and Chhattisgarh (−23.7%) are also significantly below normal, a critical correction from pre-season estimates that had central India in a more favourable category.
The northeast is not a uniform zone of relief in 2026. Meghalaya — one of the wettest regions on Earth — faces a significant deficit (−65% JJAS average). Assam dries progressively from June onward, reaching −49.7% in July. Only Manipur, Nagaland, and Sikkim retain above-normal signals, driven by orographic channelling of residual Bay of Bengal moisture that partly bypasses the El Niño suppression mechanism.
Peninsular India shows a consistent below-normal signal across June, July, and August in the May 25 CFSv2 ensemble — Kerala averaging −53%, Karnataka −51%, and Telangana −53% over these three months. The September picture is where uncertainty is highest. Earlier ensemble runs (IC May 1) showed a sharp late-season IOD-driven recovery across the peninsula; the May 25 IC run redistributes this signal differently. This divergence is expected behaviour at a four-month forecast horizon — September is the farthest lead-time month in this outlook, and the location of any IOD benefit is precisely the kind of detail that resolves progressively closer to the event. The June and July CFSv2 updates will sharpen this picture considerably.
Odisha remains the most resilient eastern state: a moderate Jun–Aug deficit (−27%) with Bay of Bengal low-pressure systems providing compensating rainfall pulses, and a near-normal September (+14%).
📅 The monthly progression is critical: June is the least affected month and may give a misleading impression of a manageable season. The real deficit story unfolds from July onward when El Niño fully asserts itself. Farmers, water resource managers, and policymakers should not extrapolate a reasonable June into a good season.
| Month | All-India Signal | Dominant Feature |
|---|---|---|
| June 2026 | Variable; NW/Central severely deficient | Onset active; El Niño imprint already evident across plains |
| July 2026 | Broadly below normal | El Niño asserting dominance; Northeast turns dry |
| August 2026 | Deeply below normal across most of India | Peak El Niño impact; even northeast dries significantly |
| September 2026 | Highest forecast uncertainty; broad signal unclear | September sits at maximum lead time — ensemble runs diverge on where any IOD benefit concentrates. Below-normal continues as central scenario; regional distribution will sharpen with June & July updates |
📊 Why September Has the Widest Uncertainty: September is the farthest month from the May 25 ensemble initialisation date — a full four-month lead. Comparing two recent CFSv2 IC runs (May 1 and May 25), the June–August signals are consistent and robust across both; September shows the largest inter-run divergence, particularly in where any IOD-driven late-season improvement concentrates. This is normal behaviour for seasonal models at extended range: the large-scale below-normal story is stable, but fine-grained regional detail in the final month resolves only as the season progresses. VayuMet will update this outlook monthly — the June update (by 28 June) will substantially reduce September uncertainty.
For the full state-wise and district-level CFSv2 seasonal precipitation and temperature forecast maps — updated with each new ensemble run — visit the VayuMet Weather Seasonal Forecast portal below.
View VayuMet Seasonal Forecast Portal →The seasonal rainfall anomaly fields presented in this article — from ECMWF SEAS5, NOAA/NCEP CFSv2, the UK Met Office GloSea6, JMA MRI-CPS3, and VayuMet's own CFSv2 analysis — are probabilistic guidance products, not deterministic forecasts.
ECMWF and NOAA/NCEP also indicate seasonal anomaly fields for the same period, but their operational products are best interpreted as probabilistic guidance rather than a single definitive national rainfall forecast. The numbers represent the central tendency of a probability distribution, not a guaranteed outcome.
VayuMet Weather presents CFSv2 and multi-model ensemble guidance as one layer of a multi-source forecasting framework, to be used alongside real-time observed data and IMD operational bulletins.
VayuMet Weather will update its CFSv2 Monsoon Outlook every month through the JJAS season. Each bulletin will incorporate the latest CFSv2 ensemble initialization, IMD observed rainfall data, and revised ENSO/IOD diagnostics.
| Bulletin | Expected Date | Focus |
|---|---|---|
| June 2026 Update | 28 June 2026 | Post-onset analysis; revised July–September outlook |
| July 2026 Update | 28 July 2026 | Mid-season assessment; August–September outlook |
| August 2026 Update | 28 August 2026 | Late-season forecast; withdrawal outlook |
| Post-Season Report | October 2026 | Full JJAS 2026 verification and analysis |
Sources: IMD Long Range Forecast April 13, 2026 (PIB) · IMD LRF Press Release PDF · SASCOF-34 Outlook Statement · WMO South Asia Below-Average Statement · WMO El Niño Likelihood Update · IRI May 2026 ENSO Quicklook · NOAA CPC CFSv2 Seasonal · VayuMet CFSv2 30-member ensemble, initialised May 25, 2026.
View VayuMet Seasonal Forecast Portal →