Nino34 SSTA Reaches La Nina Threshold

Fig. 1: The 12-week Nino SSTA observations.

Discussion: Last week, the Nino34 SSTA cooled to the La Nina threshold (Fig. 1). Other Nino SSTA regions remain in the neutral phase. The key to ENSO phase ahead is (mostly) the upper ocean heat observation and trend near and east of the Dateline. Recently, the cool waters in the eastern equatorial Pacific subsurface have strengthened and shifted eastward to the Dateline (Fig. 2). The daily southern oscillation index (SOI) was strong positive in August causing trade winds to increase to help cool the surface waters of the eastern equatorial Pacific (Fig. 3). However, since that time, the +SOI regime has ended, and SOI is mostly neutral in recent days. Consequently, the push of the Nino34 SSTA to the La Nina threshold is likely to level off. The most recent collection of Nino34 SSTA forecasts by the International Research Institute for Climate and Society reveals La Nina is likely for Q4/2024 and Q1/2025 shifting back to neutral phase during Q2/2025 (Fig. 4).

Fig. 2: The equatorial Pacific Ocean subsurface upper ocean heat anomalies.

Fig. 3: The daily southern oscillation index for the past 30 days.

Fig. 4: A collection of Nino34 SSTA forecasts by the International Research Institute for Climate and Society.