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Several weeks of warming in the surface and subsurface eastern equatorial Pacific signals an ENSO trend toward weak El Nino. But is this warming a head fake?

Highlight: Recent East Pacific Warming Continues.

Fig. 1: The 12-week Nino SSTA trend indicates sudden warming the past few weeks. The Nino34 SSTA is close to the El Nino threshold.

Summary: ENSO is in neutral phase. The Modoki-look in recent months is weakening. The equatorial East Pacific is warming and that warming is supported by vast subsurface warming associated with a Kelvin Wave. A change in ENSO toward weak El Nino is possible. However, the cooling off the West Coast of North America and that cooling extending into the tropics via the California Current is not a good sign for any possible El Nino ahead. ENSO has produced several head fakes since the 2015-16 El Nino and this may be another such event.

Discussion: The combination of an intense positive phase Indian Ocean Dipole (+IOD) and long-duration tropical East Pacific/Atlantic Madden Julian oscillation (MJO) episode caused trade winds to ease in the equatorial East Pacific allowing surface and subsurface oceanic warmth near the Dateline to shift eastward the past 2-3 weeks. Consequently, Nino SSTA regions are approaching El Nino thresholds (Fig. 1).

The daily North Pacific basin SSTA analysis identifies the weak surface warming spreading eastward in the equatorial Pacific region (Fig. 2). Farther to the north a robust warm SSTA pattern is north of Hawaii however the far northeast Pacific basin is near normal signaling the end of a recent positive phase Pacific decadal oscillation (+PDO) now in neutral phase.

The 30-day SSTA trend analysis (Fig. 3) identifies sharp cooling off the west coast of North America. For this reason – as mentioned above – the +PDO regime has ended. This change is important as the trend away from +PDO signals no evolving El Nino ahead despite the recent surprising warming. Note the cooler change SSTA pattern arcing into the tropics to the south of Hawaii (via the California Ocean Current). While the equatorial East Pacific is warming the warm SSTA pattern near the Dateline is likely to cool in November.

There’s plenty of subsurface warmth (Fig. 4) as a Kelvin Wave has formed and warrants close attention to the ENSO pattern.

Fig. 2: The North Pacific SSTA pattern identifies a new weak El Nino tendency but loss of a recent positive phase Pacific decadal oscillation.

Fig. 3: The daily North Pacific SSTA 30-day change analysis indicates vigorous cooling off the West Coast of the U.S. The cooler changes are driven into the tropics south of Hawaii.

Fig. 4: A large mass of warmer than normal ocean water near and east of the Dateline in the equatorial East Pacific.