Nino12 SSTA Vs. Brazil Rainfall Pattern
05/07/2025, 8:28 am EDT
May 2025 Climate Impact Company Monthly ENSO Outlook
Highlight: Neutral ENSO here to stay.
Executive summary: The Climate Impact Company constructed analog ENSO phase forecast valid through May 2026 yields oceanic (Nino34 SSTA) El Nino potential for later this year while the atmospheric (multivariate ENSO index) ENSO phase is neutral. Dynamic models mostly agree with neutral phase. ECMWF slightly favors El Nino while several NOAA models indicate La Nina regeneration. Forecast confidence is low therefore siding with neutral ENSO for the foreseeable future is recommended.
Discussion: As of early May 2025, ENSO phase is neutral. The daily Nino34 SSTA index is +0.17C and the trend is warming. In the equatorial East Pacific Ocean subsurface, upper-ocean heat is slightly warmer than normal, a substantial warmer change. The southern oscillation index (SOI) has shifted to neutral phase after many months of borderline La Nina (or Na Nina) characteristics. Consequently, the multivariate ENSO index (MEI) shifted to neutral phase (after an extended La Nina signature) during April. The Madden Julian oscillation (MJO) has been active. A recent shift of the convection phase shifting east of the Dateline to the tropical Atlantic Ocean caused Nino34 SSTA, SOI, and MEI to shift out of La Nina to neutral phase. The Climate Impact Company Nino34 SSTA analog forecast identifies 5 reasonably similar (ENSO) regimes from the past 30 years. Averaging the forward one-year (through May 2026) Nino34 SSTA signatures of the analog years suggest additional warming is likely and weak oceanic El Nino could form by Q4/2025 (Fig. 1). The Climate Impact Company MEI analog forecast also identifies 5 past similar regimes which average neutral atmospheric ENSO through 2025 and into 2026 (Fig. 2). The MEI analogs vary widely with 3 years favoring weak La Nina and 2 years favoring weak La Nina. A leading dynamic ENSO forecast model, the International Multi-modal Ensemble (IMME), indicates neutral ENSO for September 2025 (Fig. 3). As previously stated, the upper ocean heat east of the Dateline shifts warmer (Fig. 4). The subsurface upper ocean heat trend usually foreshadows any ENSO phase change ahead.
Fig. 1: The Climate Impact Company ENSO phase analog forecast utilizing the Nino34 SSTA index. Indicated is warm phase (El Nino) oceanic ENSO.
Fig. 2: The Climate Impact Company ENSO phase analog forecast utilizing the multivariate ENSO index. Indicated is neutral atmospheric ENSO.
Fig. 3: The International Multi-modal Ensemble (IMME) global SSTA forecast for September 2025 indicates neutral ENSO.
Fig. 4: Tracking the equatorial Pacific Ocean upper ocean heat anomalies which have recently warmed considerably.