El Nino indication looms in bureau-watched climate model

28 February 2023

The Bureau of Meteorology says one of the seven international climate models it surveys is indicating a swing to El Nino thresholds may be reached in late autumn following the decay of the current flood-driving La Nina.

Most of the models anticipate that central Pacific sea-surface temperatures will remain at neutral levels through the southern hemisphere autumn, while one model is neutral in March and April but “just touches on El Nino thresholds in May”, the bureau says in an update today.

While models suggest an increase in the risk of an El Nino developing in mid-to-late 2023, accuracy when forecasting through autumn is low, and outlooks that extend past autumn should be viewed with caution, it says.

The El Nino Southern Oscillation (ENSO) climate driver reflects swings between La Nina and El Nino conditions. El Ninos are associated with more heatwaves, reduced chance of widespread floods and an increased risk of bushfire in Australia’s southeast.

Events typically begin to develop during autumn, strengthen in winter and spring, then decay during summer and autumn of the following year.

The current La Nina, Australia’s third in a row, has weakened in the tropical Pacific Ocean and is likely near its end, the bureau says.

“Ocean indicators of La Nina have returned to neutral levels, while atmospheric indicators that remain at La Nina levels have started to weaken,” it says.

The Southern Annular Mode (SAM) index, which reflects the north-south shifts in rain-bearing westerly winds below Australia, is positive, but is expected to return to neutral values over coming weeks.

A positive SAM is typically associated with more rainfall in the east, and a reduced chance of extreme heat in spring and summer.