TAS: Records smashed as torrential rain brings flash floods to Hobart
Fri 11 May 2018
Rain and thunderstorms brought the heaviest rain on the record books to a large part of SE TAS overnight Thu 10th/Fri 11th May. The heaviest rain fell in during the middle of the night around Hobart and the Wellington Range behind the city. The BoM said it was caused when "A complex low pressure system crossed Tasmania on the 10th, then deepened to the northeast during the 11th bringing [a] strong, gusty and moist southerly flow over the state."
Some of the rainfall totals were unbelievable for Tasmania, and more akin to heavy tropical downpours. The weather station on Mount Wellington Pinnacle (kunanyi) reported 236.2mm in the 24 hours to 0900 11th, the second-highest daily fall ever recorded for TAS in May. Leslie Vale, 12km SW of Hobart and on the southern side of Mt Wellington, reported 226.4mm, the third highest May daily rainfall ever in the state. Some idea of the intensity of the rain on Mt Wellington summit is given by their 7-hour total of 151.8mm between 2100 10th and 0400 11th, and of that 58.4mm fell in the hour from 2200 to 2300 11th with 20.2mm falling in 10 minutes to 2240. Conditions on the summit must have been unbearable, because, on top of the torrential rain, wind gusted to 132km/h at 2000.
The Hobart BoM Regional Office in Ellerslie Road, close to the centre of the city, recorded 129.2mm for the 24 hours to 0900 11th, nearly trebling its previous May record of 47.0mm in a 125-year history. 43mm of that fell in just one hour. Also to 0900, the Bureau's office recorded its windiest 24 hours in May in a 68-year history with an average of 39.1km/h. The large number of May and all-time records broken indicate how widespread and exceptional this event was.
The resulting fast-flowing flash flooding off the mountains caused widespread damage to buildings, vehicles and public infrastructure, with estimates by the end of May indicating nearly $30m in insurance claims in addition to nearly $30m in damage to municipal infrastructure. The Guardian gave this detailed account of the event, including social media posts while it was happening. This video compilation by the ABC shows the flash flooding in progress. Over 13,000 properties lost power, while 19 schools and the University of Tasmania's Sandy Bay Campus were closed due to flooding or safety concerns [SMH].
In the aftermath, well documented in this ABC photo gallery, the Insurance Council of Australia declared the event a catastrophe, opening a hotline to help prioritise mounting claims. The ABC opened a live reporting page, and Tasmanian emergency services briefed the media. As usually happens, early reports during the clean-up underestimated its severity, but by Monday 14th a clearer picture was emerging, with insurance claims put at $20m and rising. [ABC]
The day after the event, Adam Morgan, Senior Meteorologist at the BoM, wrote in The Conversation about the meteorology behind it, and the difficulties in forecasting such an event. On a lighter note, The Guardian cartoonist, First Dog on the Moon, himself a resident in the affected area, provided his take on the events of the night.
VIC, NSW: Cold outbreak brings low-level snow
Fri 11 May 2018
A sub-polar outbreak brought a sudden change to winter across VIC and NSW from Thursday 10th to Friday 11th May. A loop in the upper air flow produced a cut-off system that moved northwards into VIC and southern NSW dragging what for May are exceptionally low temperatures of around -3 at 1.3km and -32 at 5.5km in a line from western VIC to the NSW Central Tablelands.
This one-week animation of Himawari-8 satellite water vapour images shows the whole event [Andrew Miskelly]. Watch on Wednesday 9th and Thursday 10th as the large area of white (cold) and blue (colder) cloud SW of TAS is cut off from the main westerly flow, then shoots due north up the West Coast of TAS into VIC and southern NSW. By Saturday 11th it has moved out into the Tasman, poised to bring heavy rain to New Zealand later in the week.
In VIC, Ballarat reported a temperature on Thursday of only 2.8° around midday, while Gordon, 20km to the E and at 600m above sea level, was reporting snow. Good amounts of settled snow fell in Omeo (700m) while in NE VIC, social media showed snow falling at Mount Beauty (400m). The cold front began moving through the Southern and Central Tablelands of NSW early Thursday afternoon, dropping temperatures sharply. Around 13.00 it was 25° in Sydney but only 8° in Canberra. Snow began falling on the higher parts of the Southern and Central Tablelands in the early hours of Friday 11th, and worked down to about the 900m level by dawn with snow reported at Crookwell, Lithgow, Oberon and Orange. Settled snow, however, was mostly restricted to areas above about 1,000m and snow depths were mostly less than 5cm.
Skiing resorts in both states reported falls of 10 to 40cm, much of which had melted by Monday 14th. Unfortunately, while the system brought 25 to 40mm of rain or snow to western parts of the NSW Central Tablelands, it brought little to parched remaining areas inland of the Divide in NSW or in NW VIC.
While snow like this is not uncommon in May, the very strong winds blowing up the western side of the cut-off low were, setting many records in both states on Friday 11th, Saturday 12th and Sunday 13th.
Several low day-time maximum temperature records were broken, too, and Melbourne's top of 12.8° was its coldest this early in the year since 6 May 1970. Some wild weather and flooding was also reported in the city [Fairfax]. At least the strong wind cleared away the hazard-reduction burn smoke that has been lingering across NSW for many days, like this on Mt Solitary in the Blue Mountains [Fairfax; David Brown, 7].
See also: ABC, SMH, Southern Highland News