Wednesday 15 May 2024

Is this going to be one of the shorter 'neutral' periods in that dance Australia's weather conditions do between El Niño and La Niña climate patterns - approximately 44 days before the pointer swung towards "La Niña Watch"


It appears that Australia has a 50-50 chance of entering a La Niña event in the second half of 2024.

La Niña typically means:

  • Increased rainfall across much of Australia

  • Cooler daytime temperatures (south of the tropics)

  • Warmer overnight temperatures (in the north)

  • Shift in temperature extremes

  • Decreased frost risk

  • Greater tropical cyclone numbers

  • Earlier monsoon onset

According to the Australian Bureau of Meteorology: In eastern Australia, the average December-March rainfall during La Niña years is 20% higher than the long-term average, with eight of the ten wettest such periods occurring during La Niña years. This is particularly notable for the east coast, which tends to be less affected by La Niña during the winter months but can experience severe flooding during La Niña summers.

The record breaking NSW Northern Rivers floods of February-March 2022 occurred in a La Niña event - part of the 'triple dip' La Niña which occurred in 2020-2022.

Australian Bureau of Meteorology (BOM), Climate Driver Update: Climate drivers in the Pacific, Indian and Southern oceans and the Tropics

14 May 2024


La Niña Watch—some signs of La Niña formation later in 2024

La Niña Watch

The El Niño–Southern Oscillation (ENSO) is currently neutral. There are some early signs that a La Niña might form in the Pacific Ocean later in 2024. As a result, the Bureau's ENSO Outlook has shifted to La Niña Watch. When La Niña Watch criteria have been met in the past, a La Niña event has subsequently developed around 50% of the time. There is about an equal chance of neutral ENSO conditions in the same outlook period.

Sea surface temperatures (SSTs) in the central Pacific have been steadily cooling since December 2023. This surface cooling is supported by a significant amount of sub-surface cooling in the central and eastern Pacific. Recent cloud and surface pressure patterns are ENSO-neutral.

The Bureau's modelling suggests that ENSO will likely remain neutral until at least July 2024. It is important to emphasise that early signs of La Niña are most relevant to the climate of the tropical Pacific, and that the long-range forecast for Australian rainfall and temperature provides better guidance for local climate.

The Indian Ocean Dipole (IOD) is currently neutral. The most recent 2 weeks have seen the IOD index within neutral thresholds, and follow 7 weeks of the index being above the positive IOD threshold (+0.40 °C). The current SST observations suggest that recent development of a positive IOD may have stalled. If a positive IOD eventually develops, it would be earlier in the calendar year than is typical historically.

Global sea surface temperatures (SSTs) have been the warmest on record for each month between April 2023 and April 2024, with April 2024 SSTs warmer than April 2023. The global pattern of warmth is affecting the typical historical global pattern of sea surface temperatures associated with ENSO and IOD variability. As the current global ocean conditions have not been observed before, inferences of how ENSO or IOD may develop in 2024 that are based on past events may not be reliable.

The Southern Annular Mode (SAM) is currently neutral (as at 13 May). Forecasts indicate the index is mostly likely to remain neutral or become positive in the coming fortnight.

The Madden–Julian Oscillation (MJO) is currently weak. Most models forecast indicate that the MJO will remain weak before re-strengthening over the eastern Indian Ocean or Maritime Continent region from mid- to late-May.

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