Highlight: La Nina Is Weaker.
Fig. 1: The 12-week Nino region SSTA observations.
Discussion: Last week the Nino SSTA regions across the equatorial central and eastern Pacific Ocean warmed slightly indicating an intensity change of La Nina from moderate to weak (Fig. 1). The catalyst for the weaker La Nina is an east-shifting subsurface warm anomaly of ocean water known as a Kelvin Wave (Fig. 2). East-shifting Kelvin Waves are the process by which La Nina weakens and if 2 or 3 Kelvin Waves generate over a period of 3-4 months onset of El Nino can occur. Indeed, some global SSTA forecasts by at least 3 models indicate some warming in the equatorial East Pacific by June, a sign of El Nino evolution.
The Kelvin Wave is sufficiently strong to counter the lingering cold anomaly farther to the east. NOAA indicates upper ocean heat to the east of the Dateline is now neutral and if that (warming) trend continues, La Nina could fade quickly (Fig. 3).
The first influence of this potential ENSO phase change is influence on the North Atlantic tropical cyclone season. If an El Nino generates, seasonal activity will be suppressed. Forecast confidence for EL Nino later in 2022 is still low but increasing while evidence for La Nina’s demise is increasing.
Fig. 2: Subsurface temperature anomalies in the equatorial Pacific Ocean identify emergence of a Kelvin Wave shifting well east of the Dateline.
Fig. 3: NOAA/CPC indicates upper ocean heat in the equatorial Pacific Ocean to the east of the Dateline has moderated to near normal.