Category Archives: Floods

Floods and flooding

Cold outbreak – Snow, Cold, Rain and Wind – SE Australia 8 to 11 June 2021

Published by:

During August 2019, a significant cold outbreak occurred over Southern Australia that brought low level snow falls to the Blue Mountains including Katoomba and Leura as well as elevated areas of the Central Tablelands. My wife and I documented this event and for the first time ever, I saw snowfall at Leura, Katoomba, Blackheath and Mt Victoria.

The three photos attached are taken from this event. Roads were closed due to icy conditions and snow fell to low levels relatively close to Sydney.

There was also a similar event during the winter of 2020 and now another similar event has just occurred. During the period 8 to 11 June 2021, low level snow fell again across the Blue Mountains, the Central Tablelands and even elevated areas of the Northern Tablelands. In addition, the Snowy Mountains saw heavy snow falls to coincide with the start of the ski season.

The snow images seen in the above photos were again replicated at Leura, Katoomba, Blackheath and Mt Victoria. Generally, snow fell above 850 metres in elevation, roads were closed and icy conditions prevailed.

However this event was remarkable in that Sydney (Observatory Hill) saw its coldest day in decades in which the maximum temperature reached 10.3C following a minimum of just 6.7C (10/6/2021). However what is more remarkable is that this temperature occurred under northern winds. Frigid air was circulating around an intense low pressure cell so that the northerly winds had in fact originated from the south.

It reached a maximum of just 8.9C at Horsley Park and 9.5C at Parramatta.

It is suggested in the media that this could have been the coldest day in 37 years while other media reports suggests that it has not been this cold since 1899.

Some old weather records for Sydney have been reviewed and it is determined that the recent cold day is not the coldest ever recorded for the city as there have been colder days. However, cold days where the maximum temperature fails to reach 10C are rare. Sydney has grown over the years and there are records for Sydney Observatory Hill going back to 1859 and hence the coldest winter days have been:-

Maximum 7.7C on the 19 July 1868.

Maximum 9.1C on the 9 August 1872.

Maximum 9.7C on the 13 June 1899.

Maximum 9.5C on the 8 September 1869.

There is suggestion of a very rare cold day on the 28 June 1836 as reported in the Sydney Morning Herald and around 6 am, the temperature was around 38F (Roughly 3.3C) and it began to snow in the morning with the snow lasting a few hours. It is claimed that the maximum temperature reached 50F (Roughly 9C later that day). This cold day occurred 23 years before weather records began. This event is controversial as there are questions as to whether it was soft hail or actual snow and what instruments were being used to record the temperatures. Either way, the 28 June 1836 was a cold day but whether it was actual snow or soft hail will probably never be known.

The cold day Sydney just experienced was not the coldest on record, but it is rare to see such low temperatures given Sydney’s location and its climate.

There is an account of the 1836 event attached to this post and the fact that snow is suggested in the forecast or weather conditions being experienced for Sydney does make it significant.

The coldest maximum temperature that can be found for Richmond is 9.5C on the 13/7/2011. It reached 8.3C on Thursday which would make it a new maximum low for this weather station and colder than the 11.5C recorded as the maximum day temperature for the 27 June 2007. Records only go back to 1994 at this weather station.

Other low maximum day temperatures for Thursday include:-

Sydney region

Parramatta 9.5C.

Horsley Park 8.9C.

Penrith 8.3C.

Regional and Rural New South Wales (Including)

Albury Airport - 9.8C.

Armidale 5.6C (At Armidale, it reached 7.6C on the 9/6/21 and 9.7C on the 11/6/21).

Cooma 3.2C with a minimum of 0.0C.

Glenn Innes 5.1C.

Goulburn 6.9C with a minimum of -1.7C.

Orange -0.3C to a maximum of 3C.

Oberon -2C to 5.2C.

Rainfall

The same system also brought some significant rain to certain areas. While Sydney received light to moderate falls some of the rainfall that occurred elsewhere was remarkable given location.

Victoria

An area to the south of the Great Dividing Range but east of Melbourne received some heavy rainfall which resulted in flooding. Flooding was observed around Taralgon as well. Some of the heaviest falls for the 24 hours to the 10 June 2021 include:-

Thompson Yarra Divide - 241 mm.

Licola - 170 mm.

Noojee - 154 mm.

Reeves Knob - 144 mm.

The hilly areas of outer Melbourne’s east received between 50 and 100 mm. In addition to the rain, power was lost and trees were brought down due to wind and a clean up is currently underway.

New South Wales

Perisha Valley - 62 mm (Mostly as snow).

Thredbo - 50 mm (Mostly as snow).

A rain event across parts of the Central West of New South Wales saw good totals of up to 42 mm falling including 42 mm at Dubbo, 40 mm at Barina, 38 mm at Neura and 36 mm at Coonabarabran.

Wind

There were instances of wind damage and trees being felled especially across snow affected areas and across southern Victoria. However, the strongest wind gusts occurred at Mt William (The Grampians) where a single gust of 115 km/h occurred. Further, the lighthouse at Wilsons Promontory recorded one wind gust of 111 km/h at 2.30 am on the 10/6/2021 and the Puckapunyal West (Defense) weather station recorded a single gust to 111 km/h at 3 am on the same day.

At Mt Buller, peak winds gusts reached between 104 to 107 km/h for the 10/6/2021.

As such, this was a dynamic weather system that has created a wind range of weather that has disrupted large swathes of South East Australia. During Friday, conditions moderated dramatically allowing for a clean up to occur including a gradual warming of daytime temperatures.

North Indian Ocean – Tropical Cyclone Tauktae – 15 to 18 May 2021

Published by:

A look at the Worlds tropical cyclone tracks will reveal that the majority of all tropical storms form within certain ocean areas including the north west Pacific Ocean, an area of the west coast of Central America and Mexico, the tropical Atlantic Ocean north of the Equator including the Gulf of Mexico, the Western Pacific Ocean including areas within Australian waters and the tropical Indian Ocean within the southern hemisphere between Australia and Africa.

There is also another area where such storms can occur but are much less likely being the North Indian Ocean situated between India and the Arabian Peninsula. Occasionally a storm will form within this area and track towards the North West India / Southern coast of Pakistan but instances of such occurrence are relatively rare.

During the period 15 to the 18 May 2021 a significant tropical storm has formed within an area where tropical cyclones are generally rare. This storm was named Tropical Cyclone Tauktae which formed off the west coast of India then tracked northwards towards the north west coast of India and even threatened the south east coast of Pakistan. Landfall occurred between Porbandar and Mahuva (Gujarat State - India).

At peak intensity, this storm reached Category 4 on the Saffir Simpson Scale with peak wind gusts at the core of at least 115 knots (Approximately 213 km/h). This storm was supported by ocean waters within the range of 30 to 31C and atmospheric conditions were certainly favourable for supporting such a strong storm. Strong convection and thunderstorm cells were visible on satellite images especially to the south of the eye which supported the storm. This storm weakened just before commencing landfall over Gujarat State.

This storm has brought heavy rain especially around Saurashtra and numerous west coast localities were warned for heavy rain as the storm tracked northwards. Media reports suggests a significant impact onto the north west Indian coast with at least 26 fatalities mainly within coastal locations, flooding, heavy rain and intense wind gusts. It is believed that upwards of 200,000 residents were evacuated prior to the storm making landfall.

The images attached to this post are taken from Worldview and CIMSS. Information was also sought from the India Meteorological Department 17/5/2021 prior to the storm making landfall.

Heavy rain and flooding – New South Wales South Coast – 4 to 7 May 2021

Published by:

Following an exceptionally wet March and a subsequent dry April 2021, the first week of May 2021 across the east coast of Australia has again been wet.

The initial Bureau of Meteorology rain models suggested that upwards of 50 mm of rain would fall across much of the east coast especially along the coastal strip of New South Wales south of Sydney. Models suggested slightly heavier falls of between 50 mm and 100 mm could fall in isolated locations. The event would not have been considered significant for the 4 day period.

However, rainfall totals in some locations south of Sydney especially within the Shoalhaven region, an area between Ulludulla and Batemans Bay and around Bega not only exceeded expectations but have been heavy leading to isolated flooding events.

Accumulative totals have reached between 200 mm and 300 mm for the event and even across Sydney rainfall totals exceeded expectations. As a result, moderate flooding has occurred at Menangle Bridge on the Nepean River south west of Sydney and minor flooding has occurred along the Shoalhaven River at Nowra.

Some of the daily rainfall totals have been considerable during this event although falls over 100 mm have been concentrated within small localities.

For the 24 hours to 9 am 5/5/2021, the heaviest rainfall totals include:-

Black Range (Near Bega) 156 mm.

Bega River at Kanoona 123 mm.

Bega - 122 mm.

Lake Tabourie - 100 mm.

Angledale - 119 mm.

All localities except Lake Tabourie are close to Bega on the New South Wales South Coast.

For the 24 hours to 9 am 6/5/2021 some rainfall totals include:-

Brogers No 2 (Brogers Creek) - 129 mm.

Fitzroy Falls Dam - 114 mm.

Nowra ASW - 113 mm.

Brooman (Directly north of Batemans Bay) - 104 mm.

Such falls were limited to small areas. Here in Sydney rainfall totals ranged from 8.2 mm at Penrith to 40 mm at Lucas Heights for the 24 hours to 9 am 6/5/2021. There were short bursts of heavy showers throughout the day but for the most part, most rainfall totals across much of Sydney fell between 20 mm and 26 mm.

For the 24 hours to 9 am 7/5/2021, even heavier rainfall totals occurred within small areas south west of Wollongong encompassing the Kangaroo Valley, parts of the Shoalhaven region and the eastern side of the Southern Highlands around Fitzroy Falls and Robertson. The heaviest totals include:-

Brogers No 2 (Brogers Creek) - 182 mm.

Fitroy Falls Dam - 171 mm.

Beaumont (The Cedars) - 162 mm.

East Kangaloon - 156 mm.

Robertson - 147 mm.

It is clear that Brogers No 2 (Brogers Creek) has had more than 300 mm during this rain event.

The weekly rainfall plot for New South Wales to May 7 2021 on the Water and the Land site clearly shows that large parts of the New South Wales South Coast has recorded between 200 mm and 300 mm of rain including an area south west of Wollongong, an area between Ulludulla and Batemans Bay and another small area close to Bega.

This event has impacted the Warragamba Dam catchment and it is likely that more water inflows will result in water spilling again over the dam wall.

Conditions are now clearing and further significant rainfall is not likely from this system. This will allow flood waters that have occurred to subside.

s2Member®