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Rainfall - May 2024

Min Temperature
Max Temperature
Rainfall chart image for May 2024

La Nina Watch declared; Positive IOD stalling

Joel Pippard
15 May 2024, 12:12 AM UTC

ENSO status: La Niña Watch declared.
IOD status: Neutral, becoming positive.
SAM status: Neutral, favouring positive in winter.

Rainfall outlooks are showing slightly below average rainfall over winter (mostly June and July) for WA, and most of SA, Vic and Tas. Conversely, above average rainfall is expected for eastern parts of Qld and NSW, and potentially eastern Tas. Outlooks turn close to average in August throughout mainland Australia, with Tas still showing drier than normal.

Temperature outlooks are indicating warmer-than-average maximum and minimum temperatures over autumn and winter for near all of the country, mainly due to higher-than-normal ocean temperatures surrounding Australia. Small pockets of central-north Qld could see cooler than average temperatures, most likely due to enhanced easterly winds.

The El Niño Southern Oscillation (ENSO) is now in a La Niña Watch, meaning there is approximately a 50% chance of a La Niña developing this year. Ocean cooling is occurring in the eastern Pacific, with 3 out of 7 global models forecasting a La Niña to develop in 2024. Warmer than normal waters are situated in the Coral Sea, providing moisture and humidity to the east coast. The atmosphere continues to be neutral. A La Niña typically increases rainfall, cools daytime temperatures and increases nighttime temperatures over central Australia, Qld and NSW, but has little effect on southern WA, SA, Vic and Tas during winter.

The Indian Ocean Dipole (IOD) is in a neutral phase. Ocean temperatures are at record levels in the western Indian Ocean, and upwelling is occurring along the Java Coast in Indonesia. However, the upwelling is mostly occurring outside the IOD East region, and is therefore not reflected in the IOD Index, which is sitting just below thresholds. Persistent southeasterly winds have set in, and look to remain strong despite a burst of tropical activity in the region. Models are suggest a tropical low could form in the Bay of Bengal over the coming fortnight, that would help solidify a positive IOD event. A positive IOD reduces the number of northwest cloudbands that cross Australia during winter and spring, therefore reducing rainfall, increasing maximum temperatures, but decreasing minimum temperatures.

The Southern Annular Mode (SAM) is neutral but is expected to favour a positive phase during winter. Furthermore, the long-wave pattern around Antartica is favouring high pressure near Australia for most of June and July, akin to a positive SAM. A positive SAM increases high pressure and easterly winds across Australia. This leads to increased rainfall and thunderstorm activity with cooler days but warmer nights in the east. It also reduces cold fronts, and therefore rainfal, while leading to warmer days and colder nights over southern Australia, particularly for southwest WA.

This page displays long-range climate outlooks for Australia, which are not the same as weather forecasts. The main difference between climate outlooks and weather forecasts is scale. A weather forecast aims to predict the weather for an individual location on a scale of hours to days. A climate outlook predicts the average weather conditions over a broad area, relative to the long-term-average, on a scale of weeks to months. For example, a climate outlook can let you know if the upcoming season will be drier or hotter than usual. However, there can still be individual days of heavy rain and cold weather in the season.