Friday 21 June 2024
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La Niña weakens, although atmospheric signal persists

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MELBOURNE, Australia – The 2021–22 La Niña event continues to weaken, with oceanic indicators mostly at neutral levels reports the Bureau of Meteorology of the Australian Government in its latest update. However, atmospheric indicators remain above La Niña thresholds, meaning La Niña’s influence continues.

Sea surface temperatures in the tropical Pacific are cooler than average but have been at neutral levels for much of April. Beneath the surface, waters also remain slightly cooler than average.

However, in the atmosphere, indicators remain at typical La Niña levels, with stronger than average trade winds in the western Pacific and decreased cloudiness across the tropical Pacific region.

The Southern Oscillation Index (SOI) also continues at moderate to strong La Niña levels, although this signal is dominated by conditions at Tahiti.

Six of seven climate models surveyed by the Bureau indicate a return to neutral El Niño–Southern Oscillation (ENSO)—neither La Niña nor El Niño—during the late southern hemisphere autumn or in early winter. Only one model continues La Niña conditions through winter.

The Indian Ocean Dipole (IOD) is neutral. Outlooks for the IOD show a negative IOD developing in the coming months. While model outlooks have low accuracy at this time of year and hence some caution should be taken with IOD outlooks beyond May, there is consistency across the forecasts from all international models. A neutral IOD has little influence on Australian climate. A negative IOD increases the chances of above average winter–spring rainfall for much of Australia. It also increases the chances of warmer days and nights for northern Australia.

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The Southern Annular Mode (SAM) index is currently neutral, but is expected to briefly dip to negative levels with neutral to positive levels thereafter for the coming two to three weeks. During autumn SAM typically has a weaker influence on Australian rainfall.

The Madden–Julian Oscillation (MJO) has recently become weak. Climate models indicate the MJO is likely to remain weak, having little influence on tropical weather and climate in the coming fortnight.

Climate change continues to influence Australian and global climate. Australia’s climate has warmed by around 1.47 °C for the 1910–2020 period. Southern Australia has seen a reduction of 10–20% in cool season (April–October) rainfall in recent decades, while rainfall across northern Australia during its wet season (October–April) has increased.

In recent decades there has been a trend towards a greater proportion of rainfall from high intensity short duration rainfall events, especially across northern Australia.

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