Highlight: Nino34 SSTA zooms past the La Nina threshold last week.
Discussion: Last week the Nino34 SSTA region (where ENSO phase is monitored) dipped to -0.9C which is well within the La Nina threshold (Fig. 1). The Nino3 region also turned cooler dipping beneath the La Nina threshold. Near the Dateline and off the northwest coast of South America SSTA is neutral. In the subsurface, the eastern equatorial Pacific Ocean has turned much cooler and certainly supports the cooler Nino34 SSTA observation (Fig. 2). Given the cool subsurface, the Nino34 SSTA is likely to strengthen and if so La Nina onset should be announced no later than early October.
Fig. 1: The 12-week Nino SSTA region monitor indicates sharply cooler SSTA for the Nino34 region last week and certainly within the La Nina threshold.
Fig. 2: Subsurface equatorial Pacific Ocean temperature anomalies. Cool East Pacific is trending much cooler just-after mid-August.