Subsurface Equatorial Pacific Is Cooling…Supports La Nina Onset Q4/2021

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In the weekly ENSO diagnostics report we take a look at the continued cooling in the subsurface equatorial Pacific Ocean signaling La Nina onset for Q4 of 2021.

Discussion: The Nino SSTA regions were steady neutral phase for the second week in a row last week (Fig. 1). An interesting development in the subsurface…the cool anomaly in the equatorial East Pacific is shifting westward toward the Dateline while warm waters in the equatorial subsurface West Pacific are less warm (Fig. 2). The monthly subsurface upper ocean heat analysis across the equatorial Pacific continues to steadily cool and is very supportive of returning La Nina (Fig. 3). The southern oscillation index (SOI), a measure of the atmospheric reaction to ocean SSTA patterns has favored La Nina since mid-2021 (Fig. 4). ENSO is in neutral phase but subsurface cooling supports La Nina development during quarter 4 of 2021.

Fig. 1: The 12-week Nino SSTA region monitor indicates steady neutral phase the past 2 weeks.

Fig. 2: Subsurface equatorial Pacific Ocean upper ocean heat analysis for last week.  

Fig. 3: Equatorial Pacific Ocean subsurface equatorial het anomalies for the past 12 months.

Fig. 4: Monthly southern oscillation index (SOI) for the past 12 months.