ENSO ADVISORY NO. 2

742 PM EST Thu. Feb. 25, 2016

 

SYNOPSIS: A transition to ENSO-neutral is likely during late Northern Hemisphere spring or early summer 2016, with a possible transition to La Niña conditions during the fall.

Sea surface temperature anomalies were in excess of 2C across the east-central equatorial Pacific Ocean. The Nino indices in the eastern Pacific declined, while Nino 3.4, and 4 were nearly unchanged. The sub-surface temperatures in the central and eastern Pacific increased due to a downwelling Kelvin wave, but toward the end of the month weakened again in association with the eastward shift of below normal temperatures at depth in the central Pacific. Also, low-level westerly wind anomalies and upper-level easterly wind anomalies continued across much of the tropical Pacific. The traditional and equatorial Southern Oscillation Index values remained negative but weakened relative to last month. Convection remained much enhanced over the central and east-central tropical Pacific and suppressed over Indonesia.

UPDATE:  During the last four weeks, tropical sea surface temperatures were above average across most of the Pacific.  During the last four weeks, tropical sea surface temperatures were above average across the most of the Pacific and the Indian Ocean. During the last four weeks, positive sea surface temperatures anomalies persisted across most of the equatorial Pacific, with diminishing strength in the far eastern Pacific. Sea surface temperatures anomalies decreased in the eastern equatorial Pacific and increased near the Date Line. The basin-wide equatorial upper ocean (0-300 m) heat content is greatest prior to and during the early stages of a Pacific warm episode, and least prior to and during the early stages of a cold episode.  The slope of the oceanic thermocline is least (greatest) during warm (cold) episodes.

 

Recent values of the upper-ocean heat anomalies (positive) and thermocline slope index (negative) reflect El Nino. During January–March 2015, a significant sub-surface warming occurred across the eastern Pacific. During August through late September, positive anomalies decreased. Positive anomalies decreased during November and December, increased during the first half of January 2016, and have recently decreased.

 

Downwelling phases of a Kelvin wave were observed in March-April, mid-May to late June, July-August, and October to November. During August and September, positive subsurface temperature anomalies slowly shifted eastward. More recently, the downwelling phase of a Kelvin wave has shifted eastward into the eastern Pacific, while an upwelling phase is apparent in the central Pacific.

 

Anomalous upper-level divergence and convergence have generally persisted over the Central/Eastern Pacific and Indonesia, respectively. Sub-seasonal or Madden-Julian Oscillation (MJO) activity contributed to an eastward propagation of regions of upper-level divergence and convergence during late October-early November 2015 and more recently in December and January 2016. The positive Indian Ocean Dipole (IOD) event persists. This event has been in place for over three months. International climate models expect the positive IOD to break down during November and early December. More broadly, Indian Ocean temperatures remain very warm: the October sea surface temperatures anomaly for the southern hemisphere Indian Ocean was the highest positive anomaly for any month on record.

Jim G. Munley, jr.
http://www.jimmunleywx.com



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