Intense Kelvin Wave Shifting East Across Pacific Could Dissipate La Nina by April

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Discussion: An intensifying Kelvin Wave, a large area of warmer-than-normal water in the equatorial subsurface, is moving east of the Dateline (Fig. 1). If the Kelvin Wave remains intact while continuing an easterly trek through the equatorial East Pacific changes to the climate pattern will occur.

The changes include…

  • Immediate dissipation of La Nina.
  • Warming of the East Pacific such that another Kelvin Wave could flip ENSO to an El Nino.
  • The best way to push a Kelvin Wave across the equatorial Pacific is with interaction of the Madden Julian oscillation.
  • If the MJO/Kelvin Wave link is established the risk of major weather events across the U.S., focused mainly on flooding rainfall will occur.

Upper ocean heat analysis identifies a robust large area of anomalous warmth emerging in the central equatorial Pacific (Fig. 2). Upper ocean heat east of the Dateline is now shifting into the warmer-than-normal category (Fig. 3) coupling lingering cool waters in the upper ocean of the eastern equatorial East Pacific coupled with robust warming toward the Dateline.

The required MJO scenario to combine with the Kelvin Wave to produce hostile storms across the U.S. is an enhanced phase 6/7 (Pacific Ocean). The 30-day forecast issued by ECMWF does not indicate this scenario over the next 30 days (Fig. 4). Therefore a very slow east drift of the Kelvin Wave is expected. Without MJO Help the Kelvin Wave should reach the northwest coast of South America and dissipate La Nina in early April.

The Nino SSTA regions warmed slightly last week although weak La Nina remains intact (Fig. 5).

Conclusion: Monitoring a Kelvin Wave now moving east of the Dateline and intensifying is extremely important as to a potential rapid dissipation of La Nina during early calendar spring. The dissipation of La Nina process would likely produce extreme storms (flooding) in the U.S. due to the energy release to the atmosphere of a Madden Julian oscillation episode coupled with an oceanic Kelvin Wave. These conditions are not indicated by forecast models – yet. However, risk of the identified conditions is increasing for around April 1st due to the increasing strength of the Kelvin Wave.

Fig. 1: NOAA analysis identifies a robust Kelvin Wave east of the Dateline.

Fig. 2: Upper ocean heat anomalies across the entire equatorial Pacific.

Fig. 3: Upper ocean heat of the Pacific Ocean east of the Dateline.

Fig. 4: The ECMWF 30-day MJO forecast indicates a weak signature for week 3 and 4 ahead.

Fig. 5: The Nino SSTA observations for the past 12 weeks are indicated.