Sunday, December 15, 2019

Will the West Pacific trade winds die down around January 4th 2020?

The following figure shows that the West Pacific trade winds died down around the 17th of September 2019 and two tropical months (i.e. 56.4 days) later around 10th of November 2010.


Just prior to these two dates, a hybrid combination of an Equatorial Rosby wave and Equatorial Kevin wave, known as a Madden Julian Oscillation (MJO), past just north of Papua New Guinea.
Associated with the Rosby wave component of the MJO were a pair of tropical low-pressure cells located on either side of the Equator that produced a burst of strong westerly winds that dramatically reduced the strength of the West Pacific trade winds a few days later.

The figure below displays the time-longitude plots for 850 hPa westerly wind anomalies covering this period of time. It clearly shows the Aug-Sep and Oct-Nov MJO events that "kill" the West Pacific trade winds around September 17th and November 10th.

If this pattern repeats itself, then we should expect the strength of West Pacific Trade winds to die down around January 4th, 2020. It will be interesting to see if this is enough to tip the Pacific in its EL Nino mode or will it require a couple more of these (lunar-driven) events.

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