Island Climate Update 248 - May 2021

The NINO3.4 Index anomaly (in the central Pacific) during April was -0.30⁰C and the SOI (Southern Oscillation Index) was +0.3, both within the neutral range. Despite the transition to ENSO neutral, atmospheric patterns may continue to be reflective of La Niña for some time to come due to its lag effect –this means that dry conditions and potential water stress may persist in island groups that have experienced dry conditions during recent months.

In the subsurface equatorial Pacific, substantial warming over the past several months is now surfacing in the eastern part of the basin. As a result of this the La Niñabase state has almost entirely faded, with a weak, remnant cool pool still lingering near the surface in the central Pacific. Accordingly, upper-oceanic heat content continued to increase.

According to the consensus from international models, the probability for ENSO neutral conditions is 78% for May to July. For August to October and November to January, the probability for ENSO neutral is 53% and 43%, respectively.

During early and mid April, a strong active pulse of the Madden-Julian Oscillation (MJO) moved over the Maritime Continent and the Western Pacific. This resulted in the formation of two late seasontropical systems, Severe Tropical Cyclone Sejora(Australia region) and Super Typhoon Surigae(North Pacific).

The tropical cyclone season is over. With the MJO active over Africa and the Indian Ocean early in May, out-of-season tropical cyclone development is unlikely in the Southwest Pacific.

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