La Nina to be announced today

I'm reasonably certain (this time!) that the Australian Bureau of Meteorology will announce today that La Nina weather conditions now exist in the Pacific ocean. Here are some reasons why:

  1. The Southern Oscillation Index (SOI) is now in positive territory (currently about +12). In order for La Nina to exist, the air pressure in Tahiti must be greater than the air pressure in Darwin (at the moment, the positive SOI figure indicates that this is so).
  2. The water in the Eastern Pacific needs to be considerably cooler than the water in the Western Pacific, which it currently is.
La Nina brings wet winter weather to South Eastern Australia. For the past three weeks, four intense low pressure systems have formed off the East coast of Australia (one of which is active now) and have dumped large amounts of rain.

The BOM says
Renewed signs of La NiƱa development

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