General background on the oscillation itself, for context alongside the live reading above.

The number above is NOAA CPC's weekly Niño3.4 anomaly -- the fastest-updating reading this site has, and what the AI summary below draws on. RONI, shown underneath, is a 3-month running mean (e.g. "AMJ 2026" = the April-May-June average): CPC's officially-confirmed index, but slower to move. During a fast-moving swing the weekly figure will typically run ahead of RONI, and both can differ from the "CPC: ..." Alert Status badge, which CPC moves to Advisory/Watch as soon as one season crosses threshold, ahead of RONI's five-season persistence rule. All three are legitimate readings of the same event, just answering different questions: what's SST doing right now (weekly), has a multi-month state been confirmed (RONI), or has CPC flagged it operationally (Alert Status)?

What

A recurring, irregular (roughly 2–7 year) warming and cooling cycle in sea-surface temperature, driven by coupled ocean-atmosphere interaction.

Ocean

Tropical Pacific Ocean.

Most effective

Centered on the equatorial Pacific (the Niño 3.4 region this site's RONI index tracks), with atmospheric teleconnections that reach South Asia mainly by shifting the Walker circulation and, with it, the summer monsoon.

• El Niño (warm phase) Equatorial Pacific SSTs above average; tends to weaken the South Asian summer monsoon, favoring below-normal rainfall and drought risk over India.
• La Niña (cool phase) Equatorial Pacific SSTs below average; tends to strengthen the South Asian summer monsoon, favoring above-normal rainfall.
• Neutral SSTs near average; no strong Pacific-driven monsoon signal, so other factors (IOD, MJO, local conditions) dominate.

General background on the oscillation itself, for context alongside the live reading above.

What

An irregular oscillation in the sea-surface temperature difference between the western and eastern tropical Indian Ocean, measured by the Dipole Mode Index (DMI).

Ocean

Tropical Indian Ocean.

Most effective

The SST gradient between the western Indian Ocean (off the Horn of Africa) and the southeastern Indian Ocean (off Sumatra), which in turn modulates rainfall across South and Southeast Asia.

• Positive IOD Warmer water in the west, cooler in the east; tends to enhance monsoon rainfall over India and South Asia, while favoring drought over Indonesia and eastern Australia.
• Negative IOD Cooler water in the west, warmer in the east; tends to suppress South Asian monsoon rainfall, and can reinforce El Niño's drying effect when the two coincide.
• Neutral No strong east-west SST gradient; minimal IOD-driven influence on regional rainfall.

General background on the oscillation itself, for context alongside the live reading above.

What

An eastward-moving pulse of enhanced and suppressed tropical rainfall and convection that circles the globe roughly every 30–60 days. Unlike ENSO or the IOD, it is intraseasonal (weeks, not years).

Ocean

Originates over the Indian Ocean and propagates eastward across the Indian and Pacific Oceans along the equator.

Most effective

The Indian Ocean and Maritime Continent/western Pacific, where its convective center most strongly modulates the South Asian monsoon.

• Indian Ocean phase (RMM phases 2–3, active) Convection centered over the Indian Ocean; tends to trigger active, wet monsoon spells over South Asia.
• Maritime Continent phase (RMM phases 6–7, active) Convection centered over the Maritime Continent/western Pacific; tends to trigger monsoon break, dry spells over South Asia.
• Other-active (RMM phases 1, 4, 5, 8) Convective center elsewhere (western Hemisphere/Africa or western Pacific); mixed, indirect effect on South Asian rainfall.
• Inactive (amplitude below 1) Convective signal too weak to read reliably; little effect on the monsoon either way.

* Tentative. RONI isn't published for a month until partway through the next one, so the most recent 1–2 months shown here are filled from NOAA CPC's weekly Niño3.4 anomaly instead -- not RONI itself, and typically higher (see the ENSO card's Info for why). The current calendar month, if shown, is doubly provisional: it's still in progress, so its average will keep shifting until the month ends.

Still Neutral by NOAA's official classification: the latest reading (0.98°C, MJJ 2026) is past the ±0.5°C threshold, but an episode is only confirmed once that threshold is sustained for 5 consecutive overlapping 3-month seasons. So far 1 of the 5 required months has qualified toward an El Nino episode. Separately, CPC's real-time ENSO Alert System Status (issued 2026-07-09) already reads "El Niño Advisory." This is CPC's operational designation, which can move to Advisory or Watch as soon as one season crosses threshold with supporting atmospheric coupling, ahead of the persistence rule above.

Issued 2026-08-01 · BOM ACCESS-S IOD outlook*

* From BOM's ACCESS-S seasonal model, the same real-time source behind the "BOM real-time" reading above. CPC does not publish an equivalent IOD forecast; its Indian Ocean outlooks cover the whole basin rather than the DMI specifically. This forecast comes directly from BOM's published operational outlook, so it includes a numeric mean value in addition to category probabilities.

Still Neutral by BOM's own standard: the latest reading (0.63°C, August 2026) is past the ±0.4°C threshold, but BOM only declares Positive IOD once that's sustained for "several weeks to 3 months." So far 2 of the 4 weeks required by this site's threshold have qualified. This reading is sourced from BOM's real-time weekly IOD index, used because NOAA PSL's HadISST1.1 series (the table below) has not carried a value past May 2026. The two products track the same signal but can differ by a few tenths of a degree from month to month (see docs/DATA.md).

Cell values are mean daily RMM amplitude by month. A value of 1 or higher is considered dynamically active. Amplitude only; see below for why the dominant phase group is not shown for ROMI-filled (ringed) months.

Phase 8: the official BOM RMM record's most recent month (July 2026) had this phase on the most days, with a mean daily amplitude of 1.66 (>= 1 is considered dynamically active). For any month the table below has no official RMM value for, it's backfilled using NOAA/PSL's ROMI index instead (see docs/DATA.md's MJO staleness note). This backfill covers amplitude only, shown as ringed cells. ROMI's own dominant-phase read is far noisier than RMM's, so no phase is shown for ringed months. ROMI's real-time amplitude reading is currently 0.20 (as of July 2026).

Generated using AI, from this pipeline's own computed data (see the Outlook and Impacts tabs for the full figures, thresholds, and methodology behind each point). AI-generated text can make mistakes. Users should exercise caution before making decisions based on it, and always verify against the underlying data and sources shown elsewhere on this site.

Generated using AI, condensing NOAA CPC's own published ENSO Diagnostic Discussion into a short summary. AI-generated text can make mistakes. Users should exercise caution before making decisions based on it, and always verify against the original CPC source cited below.

Any weekly Niño-3.4 figure mentioned here reflects CPC's own discussion as of its issue date below, which can already be a couple of weeks behind the always-current weekly reading on the ENSO card above.