Key Takeaways
- May 2024 was exceptionally warm across Australia’s east, with mean temperatures up to 3 °C above the long‑term average and several cities recording their second‑warmest May on record.
- The Bureau of Meteorology predicts one of the warmest winters on record for southern states, daytime temperatures likely 1‑2 °C above recent decades (≈2‑3 °C above pre‑industrial levels).
- There is an >80 % probability of “unusually high maximums” (top 20 % of years) across the most populated regions from south‑east Queensland to Tasmania and western WA.
- El Niño‑like conditions (reduced cloud cover, fewer cold fronts) are driving the heat, while warm sea‑surface temperatures offshore slightly favour warmer minimums despite typical El Niño night‑time cooling.
- Winter rainfall is still favoured to be below average, especially in the south, raising concerns for a poor snow season; El Niño years historically cut peak snow depth by about 50 cm.
- The heat was amplified by near‑summer‑like dew points (≈4 °C above normal) and lingering moist tropical air, which also produced record‑breaking May rainfall in many eastern locations.
- Western Australia missed the May deluge but a strong front is expected to alleviate the rainfall deficit before month‑end.
Overview of Warm May and Winter Outlook
Australia’s eastern seaboard concluded an abnormally warm May, with mean temperatures ranging up to 3 °C above the long‑term average. The Bureau of Meteorology’s latest modelling indicates that this warmth is likely to persist into winter, forecasting one of the warmest winters on record for the southern states. Daytime temperatures are projected to exceed recent‑decade averages by 1‑2 °C, which translates to roughly a 2‑3 °C rise relative to pre‑industrial levels. This outlook follows a pattern of persistent high pressure and reduced cloud cover that has kept the continent unusually warm throughout autumn.
Temperature Projections and Probabilistic Forecast
Beyond the mean shift, the BOM’s probabilistic forecast shows a near‑certainty of warmer‑than‑average conditions. The chance of experiencing “unusually high maximums”—defined as maximum temperatures falling within the top 20 % of historical years—exceeds 80 % across the most populated corridors, stretching from south‑east Queensland through Tasmania and into western Western Australia. This high probability underscores the likelihood of frequent heat spikes, even if individual days vary. The forecast combines the deterministic temperature anomaly with statistical confidence, giving planners a clear signal of elevated risk for heat‑related impacts.
El Niño Influence on Day and Night Temperatures
The anticipated warmth aligns with a typical El Niño signature: diminished cloud cover allows solar radiation to boost daytime highs, while the same clear skies promote radiative cooling at night. However, warm sea‑surface temperatures developing off the southern coastline are expected to offset some of that nocturnal cooling, slightly favouring warmer minimums despite the El Niño tendency for frosty nights. Consequently, while daytime anomalies are robust, nighttime temperatures may not drop as sharply as in a classic El Niño year, leading to a overall warmer season across both extremes.
Rainfall Outlook and Dry Season Expectations
Rainfall projections remain largely unchanged from earlier outlooks, with the BOM continuing to favour below‑average precipitation nationwide, especially across the southern regions. Despite recent heavy rain events, the weekly‑updated winter rainfall outlook still signals a dry season ahead. This expectation poses challenges for water resources, agriculture, and fire risk, as the continent prepares for a period where moisture inputs are likely insufficient to meet typical demand.
Implications for Snow Season
The warm, dry winter forecast is particularly unwelcome for the alpine snow season. Historical analysis shows that El Niño years reduce peak snow depth by an average of nearly 50 cm compared with neutral years. While isolated blizzards can still deliver temporary snow cover, the overall likelihood of sustained, deep snowpack is markedly diminished. Ski resorts and downstream water users reliant on spring melt should anticipate reduced snow storage and plan accordingly.
Record‑Breaking May Temperatures in Capital Cities
The unusual heat was most evident in the nation’s capitals. Preliminary data show Sydney, Canberra, and Hobart each experienced their second‑warmest May on record, with records extending back to the 1800s. Sydney’s average overnight low reached 14.5 °C—3 °C above its long‑term mean and an all‑time high for the month since the Observatory Hill station began in 1859. Canberra’s mean minimum stood at 5.7 °C, also 3 °C above normal, with only a single night below freezing versus the typical eight sub‑zero nights. Hobart’s overall monthly mean of 13.4 °C fell just 0.2 °C shy of its 2007 record. Melbourne and Brisbane are on track for top‑five finishes, while Adelaide is likely to record its seventh‑warmest May.
Factors Behind the Heat and Wet May in the East
Several drivers combined to produce the extreme May. Anthropogenic climate change has lifted Australia’s baseline temperature by about 1.5 °C since pre‑industrial times. Persistent cloud cover trapped heat, inhibiting nocturnal cooling, while a scarcity of strong cold fronts prevented the injection of cooler, drier air from the Southern Ocean. This front deficit also allowed warm‑season moisture to linger, raising dew points to near‑summer levels—approximately 4 °C above normal in Brisbane, Sydney, and Canberra—making the air feel muggier than temperature alone would suggest. The abundant low‑level moisture set the stage for unusually heavy rainfall across much of the east.
Wet May in Eastern Regions
Despite the overall warmth, May turned out to be remarkably wet in many eastern locales. A stalled tropical air mass delivered repeated rainbands, yielding record‑breaking totals: the Gold Coast (Queensland) logged 344 mm, its wettest May since 1987; Dubbo and Tamworth (New South Wales) each received 136 mm and 102 mm respectively, the wettest since 1983; Renmark (South Australia) saw 123 mm, the wettest May on record (data back to 1889); Walpeup (Victoria) recorded 76 mm, the wettest since 1992; and Kunanyi‑Mt Wellington (Tasmania) accumulated 305 mm, the wettest May on record (data to 1961 with some gaps). These rains boosted autumn totals in parts of eastern South Australia, with Renmark accumulating 211 mm for the season—second only to the 228 mm recorded in 1974.
Western Australia Exception and Upcoming Front
Western Australia was the notable outlier, missing much of the May deluge experienced elsewhere. However, a powerful cold front is forecast to slam into the west coast later this weekend, delivering substantial rainfall that should erase the state’s deficit before the month ends at 9 am on Sunday. This system will bring a brief return to more typical seasonal conditions for WA, contrasting with the persistent warmth and wetness dominating the eastern states.
Conclusion and Seasonal Implications
The convergence of record‑setting heat, heightened probabilities of extreme maximums, and a conflicting wet‑dry signal paints a complex picture for Australia’s coming months. While the east grapples with unusually warm days and nights, coupled with significant rainfall that has alleviated some drought concerns, the west awaits a frontal reprieve. The anticipated warm, dry winter poses risks for water availability, fire danger, and snowpack, underscoring the need for adaptive management across agriculture, energy, and urban planning sectors as the continent navigates this anomalous seasonal transition.