Tropical low drowns Townsville before heading west
Thu 1 Mar 2018
Nearly 90 of the Bureau's 100 gauges in the Townsville area scored over 100mm in the 24 hours to 0900 EST Thursday as a tropical low that has been lurking in the area moved to cross the coast. Fifteen of the gauges recorded over 300mm. The low and its spiralling rain bands have been clear on Townsville radar and satellite images, at times looking like a cyclone.
The low has given the area two days of heavy and at times torrential rain. Over the 48 hours ended 0900 on the 1st, Bluewater Flood Alert station, 20km NW of Townsville CBD, recorded 453mm, 124mm of which fell in just two hours to 0600 on the 1st. Other heavy two-day totals were 408mm at Stony Creek Alert and 400 at Saunders Creek Alert, both about 40km W of the city. Deeragun Alert, west of Stony Creek, recorded 103mm in two hours to 0800 on the 1st of which 75mm fell in the first hour. Nelly Bay, on Magnetic Island just east of Townsville, gave the raingauge a workout recording 214mm in six hours to 0900 28th.
Overall, the heaviest rain fell in the 24 hours to 0900 on the 1st, with Townsville Airport recording 139.8mm, its highest one-day total since 174.6mm fell on 13 April 2014. Since that year, Townsville has suffered a lengthy drought, reducing the city's main water supply, Ross River Dam, to less than 15% capacity last week with the city under Level 3 water restrictions. With this rain that figure shot up to nearly 80% and was still rising late on the 1st.
Flash flooding was occurring in Townsville by the evening of the 28th with some residents isolated and sandbagging in progress, according to ABC News. By this time, heavy rainbands associated with lines of converging winds around the low were moving over Townsville as the low crossed the coast moving westwards. Convergence lines like these, where winds from different directions meet and are forced to rise, caused some of the heaviest falls as did the extra uplift provided by the numerous hills and mountains that fringe the city from the NW to the SE through SW.
The Haughton River at Giru SE of Townsville reported a major flood level of 3.20m just before 1830 1st, a little above the record of 3.09m set in February 2011. Moderate to major flooding was also reported in the Bohle and Black Rivers to the W of the city.
By 0500 1st, the low had moved to SE of Georgetown, and continued to drift slowly westward to lie near Cloncurry at 1100 on the 2nd. Rainfall diminished greatly once the low moved away from the coast, and the highest 24 hour totals to 0900 2nd were 81mm at Punchbowl near Julia Creek and 71 at Etta Plains NE of Cloncurry.
[NASA Modis satellite via Severe Weather Chasers, Townsville City Council]
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