December 18, 2024
On Monday, Melbournians sweltered through temperatures approaching 40°C, but a southerly change brought welcome relief. Western Sydney faced temperatures in the low 40s yesterday and experienced the same cooling effect as the change moved through.
While Brisbane has not seen extreme heat, the humidity has been nothing short of oppressive, with the apparent minimum (feels-like temperature) in the city only briefly dipping below 30°C at 2:30am this morning. The same southerly change will push through Brisbane this afternoon, bringing much-needed relief with lower humidity levels expected over the following days.
EC rainfall & wind gusts at 4pm showing the southerly change sweeping through bringing widespread showers and storms. While average falls of 20-40mm are likely, local falls may be much higher. Source: MetCentre
Flash Flooding & Localised Damaging Winds Possible in SE QLD Today
Unfortunately, the southerly change will lift the very warm and humid airmass into the atmosphere, condensing it into showers and storms. While yesterday’s activity was quite isolated, today brings a higher chance of:
Flash Flooding: Local falls of 50–80mm could occur in under an hour.
Damaging Winds: Strong levels of instability (CAPE 1500–2000j/kg) may support organised storm bands with gusty winds and higher lightning activity.
EC MU-CAPE at 1pm showing broad areas of instability though most of the storm activity will occur over the eastern districts Source: MetCentre
Typically, days with weak wind shear (like today) only result in flash flooding, but the southerly change could help keep storms moving, allowing for better organisation and stronger cells. This raises the potential for some localised riverine flooding, particularly as both the Upper Brisbane and Bremer Rivers are already in minor flood.
ACCESS sounding showing weak wind shear, high levels of moisture and moderate levels of instability over Southeast Queensland (ideal for producing heavy rainfall and flash flooding). Source: MetCentre
Heavy Rain to Shift into Northern Queensland
Areas of northern Queensland have already experienced severe storms and heavy rainfall - but that could increase further as the southerly change moves into central and northern Queensland, where it will interact with a westerly wind burst associated with the Madden-Julian Oscillation (MJO). This interaction will likely bring:
Heavy rain, showers, and storms later this week and across the weekend.
Elevated flood risks across northern Queensland, particularly in flood-prone catchments.
Potential for a tropical low
Accumulated rainfall for the next 4-5 days across Queensland with the development of a low pressure system across models. Source: MetCentre
Low Risk of Tropical Cyclone Development
We are also monitoring a developing low-pressure system for tropical cyclone potential. Currently, the likelihood remains low, but this pattern—where southeasterly changes collide with the westerly wind burst from the MJO—is sometimes conducive to tropical cyclone formation.
Gusty SE winds will collide with the westerly MJO burst across northern Australia helping to increase convergence which may result in the development of a tropical low (different to the sub-tropical low that crossed the coastline earlier this week). Source: MetCentre
The good news: If a tropical cyclone does develop, early indications suggest it will track east to southeast, away from the Australian coastline thanks to a strengthening jetstream across Australia resulting in a strong steering influence from the west. However, as forecasts remain 4–6 days out, this scenario is subject to change.
300mb winds showing a strong jetstream that should steer any tropical lows or cyclones in the Coral Sea eastwards, away from the coastline. Source: MetCentre
Preparing for the Days Ahead
While severe weather concerns will ease across large parts of eastern Australia in the coming days, residents and businesses in northern Queensland should prepare for potentially heavy rainfall and flooding risks.
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