Australian Weather

13 Dec 2025, 4:21AM UTC

Eastern Australia has experienced an active thunderstorm pattern in recent days. Amid the broader storm activity, slow-moving thunderstorms affected the Sydney Metropolitan, Illawarra, Central Tablelands and Hunter regions on Friday, prompting heavy rain warnings. This story looks at the nature of these storms, focusing on why they became slow-moving and how the atmospheric setup supported heavy rainfall.  Thunderstorms on Friday produced very intense short-duration rainfall, particularly across parts of the Central Coast, Hunter and Sydney regions.  Image. Satellite, lightning and radar imagery over central eastern NSW on Friday morning. Source: Weatherzone.  Some of the more notable short-period rainfall observations on Friday included:  Martinsville 81.0 mm in the 3 hours to 4:04 p and 57.5 mm in the 60 minutes to 2:45 pm;  Lake Macquarie 76.0 mm in the 2 hours to 2:58 pm;  Norah Head 44.2 mm in 30 minutes to 7:58 am;  Linden 61.0 mm in the 2 hours to 7:30 am;  Kangy Angy 74.5 mm in the 2 hours to 6:17 am;  Lake Macquarie 70.0 mm in the 3 hours to 3:30 am.  Across NSW, some of the higher observed rainfall totals during the 24 hours to Saturday 9am included:  Martinsville 98.5 mm;  Bulahdelah 63.5 mm;  Port Kembla 61.5 mm;  Broken Back (Cedar Creek) 52.4 mm;  Lostock 42.0 mm;  Holsworthy (Defence) 40.0 mm;  Sydney Olympic Park 38.8 mm;  Badgerys Creek 28.8 mm;  Camden 28.7 mm;  Bankstown 27.6 mm;  Kiama 25.2 mm;  Maitland Airport 24.0 mm;  Newcastle Nobbys 21.4 mm;  In southeast Queensland, thunderstorms also delivered areas of heavy rain, with standout totals including:  Coolangatta 71.0 mm;  Inner Beacon 41.0 mm;  Brisbane Airport 26.4 mm;  Gold Coast Seaway 24.4 mm;  Brisbane 22.2 mm;  Cape Moreton 22.2 mm.   Why rainfall rates were so intense in some places?  To better understand why these storms behaved the way they did, we’ll take a closer look at a skew-T diagram from Friday. Meteorologists use skew-T diagrams to analyse the vertical structure of the atmosphere. The diagram is called a skew-T because temperature lines are drawn at an angle, or “skewed”, rather than vertically, which makes it easier to interpret temperature changes with height. Skew-T diagrams help assess thunderstorm potential, storm intensity and the types of storms that may produce hazards such as heavy rain, large hail or damaging winds.  As shown in the modelled skew-T diagram below for northern parts of the Illawarra, the atmosphere on Friday was set up in a way that strongly favoured heavy rainfall. Steering winds, which are the winds that control how fast storms move, were weak through the lower and middle levels of the atmosphere, generally less than about 10-15 knots, causing storms to drift slowly rather than move away quickly. The air was also very moist, with precipitable water values close to 30-35 mm, meaning there was a large amount of moisture available to be converted into rainfall. Clouds also formed at very low levels (roughly 300-400 metres above sea level). This meant rain had only a short distance to fall through drier air, reducing evaporation and allowing rainfall to reach the ground more efficiently.   CAPE, or Convective Available Potential Energy, is a measure of how much energy is available for air parcels to rise once storms develop. In this case, moderate instability was present, with CAPE values around 400-500 J/kg. While not extreme, this was sufficient to support thunderstorm development and maintain sustained updrafts when combined with deep moisture through the atmosphere. This setup allowed storms to produce very intense rainfall rates, and because the storms moved slowly, rainfall accumulated rapidly, leading to flash flooding, particularly across urban areas and along the escarpment and ranges. Image. Modelled skew-T diagram for Friday 12th December around midday for a location in northern parts of the Illawarra, where thunderstorms with heavy rainfall developed.  What’s to come for today, Saturday?  A trough supported by an upper-level disturbance is triggering scattered severe thunderstorms across parts of inland and eastern NSW, including Sydney, with warnings for damaging winds, large hail and heavy rainfall in place as of 2pm EDT. This system will continue to move east through the remainder of today, bringing severe thunderstorms into southern Qld. Storm activity is likely to persist into Sunday, potentially impacting Brisbane as well as broader areas of northern and eastern Qld.   

11 Dec 2025, 11:47PM UTC

Parts of eastern NSW received more than 70mm of rain in two hours on Friday morning, with more heavy rain and severe thunderstorms on the way on Friday and the weekend. A coastal trough being fed with moisture-laden air from the Tasman Sea caused heavy rain and thunderstorms to soak parts of eastern NSW on Thursday night into Friday morning. Another trough extending over the state’s north and into southern Qld also triggered rain and storms over the last 24 hours. Some of the standout rainfall totals during the 24 hours ending at 9am on Friday included: 88.5 mm at Martinsville to the west of Lake Macquarie 83.5 mm at Mardi Dam near Tuggerah Lake 76.5 mm at Woodford Creek Dam in the Blue Mountains 73.6 mm at Norah Head on the Central Coast 65.8 mm at Bingara to the southwest of Inverell 63 mm at Yamba in the Northern Rivers Much of the rain that soaked central eastern NSW on Thursday night and Friday morning fell in a short period of time, with Norah Head picking up 44 mm in 30 minutes and Kangy Angy receiving 74.5 mm in two hours. This was enough to cause areas of flash flooding. Image: Radar images showing rainfall over central eastern NSW in Friday morning. Source: Weatherzone. The troughs will continue to trigger rain and thunderstorms over parts of central and northern NSW and southern Qld on Friday. This is likely to include severe thunderstorms in some areas. The Sydney and Illawarra regions will continue to see areas of heavy rain on Friday due to the lingering coastal trough. As of 10am AEDT, a severe thunderstorm warning was in place for parts of southern and western Sydney and the northern Illawarra district, including Wollongong. Image: Forecast accumulated rain during the 24 hours ending at 5am AEDT on Saturday, December 13, 2025. Source: Weatherzone. While the coastal trough should move offshore from Saturday, another trough will move in from the west and cause further showers and thunderstorms across broad areas of NSW, Qld, the ACT and Vic over the weekend. Image: Forecast accumulated rain during the 72 hours ending at 11pm AEDT on Sunday, December 14, 2025. Source: Weatherzone. Check the latest severe thunderstorm warnings for the most up to date information on storms over the next few days.