August in Queensland is renowned for its westerly winds, low humidity, and clear skies, with the occasional smoke from bushfires. However, Sunday, August 11th, was no typical August day. It began with hailstorms tracking over the southern suburbs of Townsville, followed by a broad band of showers that extended from Cairns to Coffs Harbour, covering much of the Queensland coastline. Late in the day, more hailstorms developed across central western Queensland.
A Strong Upper Cold Pool Combines with Unusually Humid Easterly Winds
The culprit is a strong upper trough and embedded upper cold pool. While this setup isn’t necessarily unusual for August, the persistent easterly winds have brought well above-average humidity, creating elevated instability that has led to the shower and storm activity. Had the same upper system occurred under a westerly wind regime, very little rainfall would have been expected.
ECWMF 500mb temperatures & low level wind barbs showing broad, easterly winds across the Coral Sea, feeding into a strong upper trough across Queensland / NSW. Source: Weatherwatch MetCentre
Heaviest Falls Likely Over Capricornia & Wide Bay & Burnett Areas
Forecast rainfall has fluctuated, but most models now agree that if heavy falls occur, they’ll most likely impact the central Queensland coastline, particularly over the Capricornia and Wide Bay & Burnett areas. This is because the small low initially expected to develop off the southern Queensland coastline is now forecasted to develop along the central Queensland coastline. It may linger there on Monday and Tuesday before tracking southeast and moving away from the region on Wednesday. If the low moves quickly off the southern Queensland coastline, which is the current favored scenario, it should reduce the potential for significant rainfall in Southeast Queensland while increasing the chances of heavier, flooding rainfall further north around the Capricornia and Wide Bay & Burnett regions.
ECWMF Monday & Tuesday accumulated 24 hour rainfall and low level wind barbs. This shows the low off the central Queensland coastline. Stronger winds here will increase convergence, potentially helping to increase rainfall here. Source: Weatherwatch MetCentre
Still Wet Over SE QLD & NE NSW but Lower Chance of Heavier Falls
This doesn’t mean Southeast Queensland is off the hook. It’s still likely to be a wet, showery, and rainy couple of days through to Wednesday as onshore, easterly winds feed moisture into the broad upper system. However, winds will be stronger and gustier further north, injecting more moisture and generating stronger levels of convergence.
Widespread 125-200mm Falls Expected for Central Eastern QLD, Decreasing Further South
Currently, falls of 50-100mm are still favored for coastal areas of Southeast Queensland, with some locally higher falls of 100-150mm possible, though these should remain localized. Further north, falls of 125-200mm may be widespread over eastern areas of Capricornia and Wide Bay, with the potential for localized, heavier falls of more than 200mm over three days. In northeast NSW, localized convergence could see average falls of 100-150mm.
ECWMF, AIFS (EC-AI), GFS & ACCESS-G next four days accumulated rainfall. Source: Weatherwatch MetCentre
Rainfall Should Ease by Late Wednesday - Spring Weather by the Weekend
Fortunately, especially for Ekka-goers, the rain and showers should ease by late Wednesday as the low tracks offshore. Weather conditions are likely to improve, with the potential for some early-spring warmth over the weekend as a warm, northwesterly flow brings above-average mid-August temperatures to much of the state.
ACCESS-G 850mb temperature anomalies on Saturday showing warm and above average temperatures not just over Queensland, but across large parts of Australia (ECWMF is more conservative, particularly in the south). Source: Weatherwatch MetCentre
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