Different flavours of La Niña - a word of caution

While scientists monitor the magnitude of cooling SSTs across the ENSO regions for La Niña strength, one could easily assume a moderate-to-strong event equates to “lots of rain, just on what scale”. Commentary from international experts this week helps to explain the nuances among La Niña events, and how each occurrence differs in terms of rainfall.

2010 v 2020 SST distribution (top image, below) shows cooler waters in the Coral and Arafura Sea regions now (red circles), when compared with 2010. These are key zones for convective moisture, feeding into northern area agricultural areas.

The 2020 La Niña, characterised by cooler waters through the Maritime continent north of Australia, are believed to be more similar to events occurring in the 1980s rather than signature events of 1998 or 2010. Whilst analogue year and statistical analysis has its critics, its useful to revisit Nov-Jan rainfall in those years.

• 1983-84 La Niña rainfall (Nov-Jan) shows NSW, SA and Southern Qld in the sweet spot with a north-west moisture flow from a warmer Indian Ocean, and drier in the tropics.

• 1988-89 La Niña rainfall (Nov-Jan) shows the main beneficiaries of the event occurring in NSW and SA, with much of Qld not achieving average 3-monthly rainfall.

At this stage, guidance suggests from a tropical forcing perspective, the 2020-21 La Niña is expected to have more activity through the Eastern Indian Ocean and less over the Maritime Continent (north of Australia). Under this scenario, summer rainfall potentially favours the mid-latitudes rather than the tropics and northern Australia.