El Nino has set in, Positive IOD likely by July, says Japanese weather body

Japan's Meteorological Agency (JMA), one of the key international agencies monitoring ENSO, has confirmed that El Niño conditions have set in for 2026. JMA's...

What Happened

Japan's Meteorological Agency (JMA), one of the key international agencies monitoring ENSO, has confirmed that El Niño conditions have set in for 2026.
JMA's forecast indicates a moderate-to-strong positive Indian Ocean Dipole (IOD) is likely to develop by mid-to-late July 2026, potentially partially offsetting the El Niño's suppressive effect on the southwest monsoon.
All four Niño-region sea surface temperature (SST) indices have been above the neutral threshold since late April 2026, with the Niño 3.4 index — the standard benchmark — at +0.4°C.
IMD's current forecast shows neutral IOD conditions during the core monsoon season (June–September), suggesting the positive IOD may arrive too late to significantly benefit peak monsoon months.
The southwest monsoon arrived over Kerala on June 4, 2026 — three days behind the normal onset date of June 1 — consistent with the El Niño pattern of delayed monsoon onset.

Static Topic Bridges

El Niño–Southern Oscillation (ENSO) — Classification and Monitoring

ENSO is the dominant mode of interannual climate variability globally. It is monitored through a network of moored buoys (TAO/TRITON array in the Pacific) and satellite observations. Multiple international agencies — NOAA (US), JMA (Japan), Australian Bureau of Meteorology (BoM), IMD (India), and the European Centre for Medium-Range Weather Forecasts (ECMWF) — issue independent ENSO outlooks, providing ensemble guidance.

Niño 3.4 region: 5°N–5°S, 120°W–170°W (central-eastern Pacific) — primary benchmark for ENSO monitoring.
Oceanic Niño Index (ONI): 3-month running mean of SST anomaly in Niño 3.4; threshold ≥ +0.5°C for El Niño, ≤ −0.5°C for La Niña.
El Niño is formally declared after five consecutive overlapping 3-month periods above the +0.5°C threshold.
JMA's El Niño Monitoring: uses 5-month running mean of SST anomaly in Niño 3 region (5°N–5°S, 90°W–150°W) as its primary index.
ENSO events typically peak in December–February (boreal winter) and dissipate by the following boreal spring.

Connection to this news: JMA's confirmation of El Niño onset is significant because its forecast — using a different regional index than NOAA — adds credibility to the multi-agency consensus that the 2026 monsoon season will be adversely affected.

Indian Ocean Dipole (IOD) — Mechanism and Monsoon Interaction

The Indian Ocean Dipole (IOD) is a coupled ocean-atmosphere climate mode, characterised by an east-west gradient in SST across the tropical Indian Ocean. A positive IOD (warmer-than-normal western Indian Ocean, cooler eastern Indian Ocean) strengthens moisture transport into the Indian subcontinent, enhancing monsoon rainfall especially over central and peninsular India, and can partially or fully counteract El Niño's drying influence.

IOD concept first described by Saji, Goswami, Vinayachandran and Yamagata (1999) in Nature.
Dipole Mode Index (DMI): difference in SST anomalies between the western Indian Ocean box (50–70°E, 10°S–10°N) and the eastern Indian Ocean box (90–110°E, 10°S–0°N); positive DMI = positive IOD.
Historical countervailing effect: positive IOD in 1983, 1994, and 1997 resulted in normal-to-above-normal monsoon rainfall in India despite concurrent El Niño events.
Negative IOD amplifies El Niño's drying effect.
The IOD season runs from June to October; it typically peaks in September–October, which is after the bulk of India's monsoon rainfall has occurred (July–August peak).

Connection to this news: JMA's forecast of positive IOD emergence by late July 2026 is encouraging but timing is critical — even a strong positive IOD developing after July may be too late to rescue kharif-season rainfall distribution in central and northwest India.

Southwest Monsoon — Onset Mechanics and ENSO Relationship

The southwest monsoon (June–September) is India's primary rainy season. Onset over Kerala is the official commencement marker, declared by IMD based on criteria including rainfall across specified stations, outgoing longwave radiation (OLR) thresholds, and wind speed/direction at 925 hPa. El Niño events are statistically associated with delayed onset, weaker circulation, and below-normal seasonal totals.

Normal onset date over Kerala: June 1 (±7 days is considered normal variation).
Four phases of monsoon: onset (June), advance (June–July), peak (July–August), withdrawal (September–October).
Monsoon delivers approximately 70–80% of India's annual precipitation.
IMD's classification: Normal = 96–104% of LPA; Above Normal = 105–110%; Excess = >110%; Below Normal = 90–95%; Deficient = <90%. LPA = 868.6 mm (base: 1971–2020).
El Niño years with positive IOD: India has seen normal monsoon in 1983 (+IOD offset), 1994 (+IOD offset), 1997 (excess monsoon despite strong El Niño). El Niño without IOD offset (e.g., 2002, 2009, 2014) caused significant deficits.

Connection to this news: The June 4 onset — three days late — is a mild early signal consistent with El Niño influence; the season's fate hinges substantially on whether the forecast positive IOD materialises with sufficient strength before the July–August peak.

Key Facts & Data

El Niño onset confirmation: JMA, May–June 2026; Niño 3.4 anomaly at +0.4°C
Southwest monsoon 2026 onset over Kerala: June 4 (normal: June 1)
JMA positive IOD forecast: likely to develop by mid-to-late July 2026
IOD season: June–October; peaks September–October
Historical El Niño + positive IOD years (normal/above-normal monsoon): 1983, 1994, 1997
India's LPA (southwest monsoon): 868.6 mm (1971–2020 base period)
IMD 2026 monsoon forecast: 90% of LPA (below-normal category)
ONI threshold for El Niño: ≥ +0.5°C for 5 consecutive overlapping 3-month periods
IOD first described: Saji et al., Nature, 1999