Island Climate Update 246 - March 2021

The NINO3.4 Index anomaly (in the central Pacific) during January was -0.68˚C, entering ENSO “cool neutral” territory (-0.5 to -0.69˚C) for the first time since August 2020. The SOI value also increased compared to January and is now on the La Niña threshold (+1.0). These trends suggest that La Nina is steadily weakening in both the ocean and atmosphere.

Of note, trade winds are expected to weaken during March in the eastern equatorial Pacific, which may allow for additional warming of SSTs.

Meanwhile, cooler than average subsurface waters persisted in the central equatorial Pacific during February, but warming was observed in the east. This signature remained consistent with the central Pacific variety of La Niña called Modoki. The persistence of the cool pool at depth in the central equatorial Pacific continues to suggest that the trend away from La Niña will be gradual rather than abrupt.

Based on the consensus from international models, the probability for the continuation of La Niña is 56% for March-May. During June-August, ENSO-neutral becomes most likely at 56%.

The convectively active phase of the Madden-Julian Oscillation (MJO) was over the western Pacific during late February and early March and was associated with the development of Severe Tropical Cyclone Niran. Niran will track very closely to New Caledonia during the first weekend of March. With the MJO exiting the region in the mid-month, the risk for additional cyclone activity is reduced.

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