Primed for El Nino, but Pacific sees warming ‘level off’

The Australian Bureau of Meteorology has picked at least two weather matrices that run counter to typical El Nino development in the tropical Pacific Ocean.

These are the positive Southern Oscillation Index values and large areas of warm water in the western Pacific and off northwest Australia.

SOI VALUES

In a typical El Nino scenario, warm waters grow in the east of the Pacific basin relative to the west.

Southern Oscillation Index, or SOI, gives an indication of the development and intensity of El Nino or alter La Niña (El Nino in reverse) events in the Pacific Ocean.

It is calculated using the pressure differences between Tahiti and Darwin. Sustained negative values of the SOI below −8 often indicate El Nino episodes.

But this index has risen over the past two weeks and has generally remained around +8 to +10. The latest approximate 30-day value to June 15 is +10.3.

Sustained positive values of the SOI above +8 may indicate a La Nina event, while sustained negative values below −8 may indicate an El Nino event.

Values of between about +8 and −8 generally indicate neutral conditions.

EL NINO WATCH

In the latest update, the Bureau said that warming of the tropical Pacific over the past several months has primed the climate system for an El Nino in 2014.

However, in the absence of the necessary atmospheric response, the warming has ‘levelled off’ in recent weeks.

But the Bureau quoted climate models to surmise that El Nino is likely to develop despite these observations and some easing in the model outlooks.

It has maintained the El Nino alert, indicating at least a 70 per cent chance of the warming of the Pacific developing in 2014.

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