Warm Equatorial Subsurface BUT East Pacific Surface Not Warming (Yet)

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The equatorial Pacific Ocean subsurface has warmed dramatically west AND east of the Dateline. However, the surface of the equatorial East Pacific has not warmed (yet).

Discussion: Upper ocean heat across the equatorial Pacific is surprisingly aggressively uniform from west of Guam in the West Pacific to the Dateline and eastward toward the northwest coast of South America. Warming from the Dateline to the northwest coast of South America is boldest and supportive of an evolving El Nino. The Nino SSTA regions have warmed to neutral phase but have been reluctant for further warming suggesting El Nino is on the horizon (Fig. 1). In fact, SSTA off the northwest coast of South America cooled slightly last week. Diminished trade winds and steady negative southern oscillation index (SOI) is necessary for the subsurface warming to show at the surface and these conditions have not fully developed (yet). The NCEP CFS V2 Nino34 SSTA forecast currently indicates weak El Nino by late summer and moderate El Nino developing in autumn (Fig. 2).

Fig. 1: Nino SSTA regions over the past 12 weeks.

Fig. 2: The latest NCEP CFS V2 ENSO phase forecast using the Nino34 SSTA Index.