PACIFIC OCEAN UPDATE - LA NINA ENDS.


These signals have been building during the last week on the longer term Euro and GFS modelling.


In March 2021, the NINO.3 sea surface temperature(SST) was below normal with a reading of -0.6°C. The five-month running mean of the NINO.3 SST departure from normal was -0.8°C in January 2021 and continued to be -0.5°C or below for 7 months beginning from last July.





That meets most global agencies criteria for reaching and maintaining a La Nina status throughout the Pacific Basin.


SSTs in the equatorial Pacific were above normal in the western part and below normal in the central and eastern parts. That contributed to widespread rainfall through Australia and flood events through northern and eastern Australia during the summer and autumn.

Subsurface temperatures were above normal in the western and central parts and below normal in the eastern part. That also has persisted into recent weeks though the signal is starting to weaken.


During the summer and early autumn, convective activity near the dateline over the equatorial Pacific was below normal, and trade winds over the central equatorial Pacific were stronger than normal. Again all indicators that La Nina is in full swing during the summer and into early Autumn.


Monthly mean SST and anomalies in the Pacific and Indian Oceans. Base period for normal is 1981-2010

Depth-longitude cross sections of temperature as well as anomalies along the equator, in the Indian and Pacific Oceans. This is from assimilated data from 1981-2010.



However the La Nina event has decayed through late March and April with the event now concluded.


The eastward movement of the subsurface warm waters is reaching the eastern equatorial Pacific, expected to continue and weaken colder-than-normal SST conditions in the eastern part soon. That will see the end of the La Nina event by the end of this month and neutralisation of the water anomalies out through the eastern Pacific will take place during May and into June.


Most climate modelling suggests that the Pacific will remain in a neutral phase for the remainder of this year - with an 80% chance of those conditions taking us through the summer 21/22.


Talk of a La Nina or El Nino redeveloping is just that, talk. No evidence from climate modelling suggests either will develop at this stage, but again those details become clearer in the coming 2 months.


This is the JMA outlook - usually very reliable and indicates that neutral phase.



So that fairly good agreement across multi agencies suggests that we will likely see little influence from the Pacific Ocean for the remainder of 2021 into early 2022.


The lagging impacts of La Nina will be felt for a little while longer with the potential for heavy rainfall along the east coast, but again not broadly supported like past events.


Rainfall for the next 6 weeks - shows that lag impact on the east coast, but finally some rainfall potential heading back to the southern and western coastlines.

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