03/09/2023, 12:39 pm EST

March 2023 Monthly ENSO Outlook: El Nino ahead for mid-year. Intensity uncertain.

Executive summary: The Madden Julian oscillation (MJO) is forecast to shift eastward across the equatorial Pacific Ocean during the next 2 weeks. Following passage of the MJO, equatorial wind shifts to west or southwest and eliminates trade winds. The lack of trade winds eliminates the up-welling process that sustains La Nina. Oceanic La Nina 2020-23 likely dissipates by March 1st. The southern oscillation index (SOI) remains in the positive phase and is forecast to remain so Discussion: As of early March, ENSO diagnostics reveal a weakening to neutral phase in the Nino34 SSTA. Implied is oceanic La Nina is ending as of March 2023. The southern oscillation index (SOI) is neutral to weak positive phase during the past week. The persistent strong positive phase, which is very supportive of La Nina, has weakened due to passage of a Madden Julian oscillation episode (MJO) through the central and eastern equatorial Pacific. Usually, MJO passage through this zone reverses SOI to negative phase. The reluctance of -SOI evolution during MJO passage implies that the unusually strong La Nina climate of 2020-23 is continuing. In the subsurface, evolving warmth is noticed as the cool waters needed to up-well to the surface by trade winds to sustain La Nina is fading. Overall, oceanic La Nina is ending while atmospheric La Nina lingers. Additional MJO activity to inspire increasing subsurface warmth of the equatorial Pacific is needed to justify El Nino forecasts for mid-year made by many dynamic model projections. The oceanic source region for MJO in the tropical Indian/West Pacific Ocean(s) remains robust warm although cooling slightly in recent weeks. The latest Climate Impact Company Nino34 SSTA analog forecast reis consistent with a non-aggressive emergence of weak El Nino by July (Fig. 1). Similarly, the long-standing +SOI regime is forecast to reverse to a weak negative phase indicating onset of El Nino mid-year (Fig. 2). Although the atmosphere-biased multivariate ENSO index (MEI) has shifted into a stronger La Nina signature than the ocean-based Nino34 SSTA since 2021, the constructed analog forecast indicates MEI reverses and catches the Nino34 SSTA warming to support weak El Nino by July (Fig. 3). The ENSO phase probability forecast is supportive of mid-year El Nino development with increasing risk of a stronger El Nino for later in 2023 (Fig. 4). The upper limit ENSO forecast which supports a faster evolution of a stronger El Nino which peaks in intensity next northern hemisphere winter (Fig. 5). Implications: The ENSO seasonal prediction barrier (SPB) is MAR/APR/MAY when ENSO phase forecast skill is lowered. Consequently, close monitoring of ENSO diagnostics (Climate Impact Company issues weekly diagnostics reports on Monday to CIC client web site) to validate predictions made now and over the next couple months must be followed closely. ENSO has limited influence on warm season climate except in the tropics. Evolution of El Nino may have limited influence on climate during summer across the northern hemisphere. ENSO influence on the climate pattern peaks during the cool season. The outlook indicates El Nino by JUN/JUL/AUG 2023. Initial significant climate influences include general dryness across the western half of the U.S., a possible wet climate in the Gulf States particularly Florida, and strong dryness emerging in Central America to the Caribbean Islands. In South America, wet weather becomes present and possibly consistent by late winter across drought-parched Argentina while the Brazil pattern is mostly wetter than normal. Dryness for Western Indonesia and Australia is likely. A positive Indian Ocean dipole (+IOD) may develop which leaves the India forecast uncertain. El Nino will lower the amount of seasonal activity in the North Atlantic basin although a warmer than normal North Atlantic may cause storms that do generate to overachieve. The East Pacific observes above normal tropical cyclone activity. Fig. 1: The Climate Impact Company Nino34 SSTA forecast reveals weak El Nino by July. Fig. 2: The Climate Impact Company southern oscillation index forecast reveals weak El Nino by July. Fig. 3: The observed Nino34 SSTA vs. MEI for the 2020-23 La Nina episode and 2023 forecast. Fig. 4: The Climate Impact Company ENSO phase probability forecast for each remaining month of 2023. Fig. 5: The upper limit ENSO probability forecast reveals a stronger El Nino ahead for 2023.