Australian Weather

06 Jul 2025, 1:24AM UTC

Fig. 1) Radar observations of rainfall on the 6th of July from 1:10 to 1:30 UTC (National Weather Service, NWS) On the eve of America’s annual celebration of the 4th of July, the Guadalupe River in southern Texas rose 26 feet (almost 8 meters) within the span of up to an hour, depending on the location. The banks of the river flooded, leading to devastating flash flooding for the Texas Hills. Rescue teams are still working to save and locate as many people as possible following this deadly flash flood event.    The torrential rains which led to the rapid rising of the Guadalupe River weren’t instantaneous. In the final days of June, Tropical Storm Barry crossed southeast Mexico. But due to a less than optimal set up, Barry was short-lived and unorganised. The tropical remnants of Barry were picked up and carried northward, where it interacted with the local storm activity of inland northern Mexico. An area of low pressure developed around Kerr County, Texas (about 140km northwest of San Antonio), which pulled this unstable and moisture-laden airmass over the Texas Hills. From the 2nd of July, heavy rainfalls were falling over the state’s south, but as the system slowed, rainfall rates increased to 2 to 4 inches an hour (50-100mm/h).     Fig. 1) Estimated rainfall over the past 2 days over the Texas Hills with a marker indicating the locations of Kerr County    The already saturated soils couldn’t hold this increased rate of rainfall, and so runoff into the Guadalupe River consequently increased from the Hills, leading to the flash flooding observed that evening. The lack of a significant dry spell between rain events (see comparison for observed rainfall over 1,3,7 days) and a slow-moving low pressure system being fed by tropical moisture, created the environment for one of the deadliest flooding events the US has seen.    Fig. 2) Estimated rainfall over the past day (left), 3-days (centre) and 7-days (right) over Texas (NWS)    Portions of the Hill country and Texas’ southeast are still under a Flood Watch, with parts of at least 8 counties still with Flash Flood Warnings as more rain is expected in the area (widespread rainfall of another 30-80mm and local falls of up to 130mm).      Fig. 3) Flood Watch for the 5th of July by the NWS    Fig. 4) Flash Flood Warning for the 5th of July by the NWS and NOAA 

05 Jul 2025, 12:36AM UTC

It’s been a busy start to the winter season for southern Australia with record breaking cold for parts of the southeast, dramatic thunderstorms in southwest WA and an East Coast Low which impacted the central and southern areas of NSW (and eastern Vic) last week, to name but a few.  The weather has taken a decidedly more settled note in the last couple of days; however, it is set to ramp up a little into the second part of the weekend.   An approaching surface low, supported in the upper levels by a cut-off low or pool of cold air will help provide the ingredients for thunderstorms across NSW on Sunday. This will provide the necessary upper support in the atmosphere to allow mild air at the surface to rise and become unstable. Once these parcels of air rise into the upper atmosphere they cool and condense to form clouds. The unstable air continues to rise higher into the atmosphere and eventually, cumulonimbus clouds form. There are the characteristic ‘towering’ clouds that can bring lightning, heavy precipitation and strong winds. Although thunderstorms are more common in the summer months due to the additional energy provided by the sun, they are not completely unusual in the Australian winter. However, this particular weather set up is more akin to spring than winter.  ECMWF accumulated precipitation for Sunday 6th July The thunderstorms are expected to be isolated at first across parts of central/east NSW but become scattered in places during the afternoon and evening as they spread erratically eastwards. A lot of places will miss out on the action, however, if you do manage to cop one it could pack a punch with the potential for heavy downpours, hail and strong wind gusts (locally damaging up to 90km/h).  The best chance of seeing a thunderstorm is for parts of the Central and northern Tablelands, the Hunter as well as the central coast (including Sydney and Newcastle) and Central Western Slopes and Plains. Keep an eye on the radar if you have outdoor plans in these regions.  The weather across NSW will return to a more settled note early next week with the action reserved for southern and central parts of both SA and Vic with a deep low over the Southern Ocean bringing stormy conditions on Tuesday and Wednesday.  To stay up to date with all the latest forecasts check https://www.weatherzone.com.au