Island Climate Update 247 - April 2021

The NINO3.4 Index anomaly (in the central Pacific) during March was -0.44˚C. This marked the first time since August 2020 that SSTs in this region were in the neutral range.  The SOI value for March was +0.1 (in the neutral range).

In the subsurface equatorial Pacific, warming continued at depth in the west and central regions during March, associated with the expansion of the western Pacific warm pool. Ocean temperatures remained marginally cooler than normal closer to the surface. This is aligned with other indicators: La Niña has waned considerably and a transition to ENSO neutral is well underway, but it will likely take an additional month for the transition to fully occur.

According to the consensus from international models, the probability for ENSO neutral conditions is 66% for April – June. For July – September, the probability for ENSO neutral is 56%.

The convectively active phase of the Madden-Julian Oscillation (MJO) was over the western Pacific during early March and was associated with the development of Severe Tropical Cyclone Niran. The MJO and its associated regional affects then moved out of the western Pacific for most of the rest of the month, leading to an extended period of suppressed tropical activity.

From late March into April, the MJO re-entered the Australasia region and then crossed into the Pacific. It may come with a slightly increased risk for regional tropical cyclone activity during the mid and late part of the month.

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