Fig. 1: Nino SSTA 12-week observations reveal slow warming and still neutral SSTA except robust El Nino warmth off the northwest coast of South America.
Discussion: All the ingredients are there, transient intense Madden Julian oscillation (MJO) to shut down trade winds, steady and intensifying negative southern oscillation index (SOI) to produce an El Nino climate, and exceptionally warm subsurface temperatures across the equatorial Pacific to fuel a developing warm ENSO. However, El Nino as defined by the Nino34 SSTA and multivariate ENSO index (MEI) is still neutral to very borderline warm ENSO. The reason? Possibly the unusual combination of warm SSTA in both the East Pacific tropics associated with developing El Nino and the West Pacific tropics where the 2020-23 La Nina warm SSTA pattern lingers.
The Nino SSTA regions indicate the very borderline El Nino SSTA conditions while the previously very warm SSTA off the northwest coast of South America is losing some intensity (Fig. 1). Note the Modoki signature has redeveloped due to the near normal SSTA at the Dateline and warmer SSTA farther eastward.
The subsurface equatorial Pacific is very warm with additional warming trend indicated in the East Pacific usually an indicator of El Nino onset and/or intensification ahead. Climate Impact Company projects formal announcement of El Nino in June.
A collection of all ENSO phase forecast models by the International Research Institute for Climate and Society reveals a wide range of forecast solutions for 2023 (Fig. 2). Dynamic models are aggressively forecasting a vigorous EL Nino ahead while statistical models (analogs) are much weaker with only a marginal El Nino in the forecast. The Climate Impact Company Nino34 SSTAS forecast indicates a robust El Nino ahead peaking by December and slowly weakening early next year.
Fig. 2: A collection of all ENSO phase forecast models and their Nino34 SSTA projection through Q1/2024.