Daily Archives: September 11, 2021

Typhoon Chanthu – 10 and 11 September 2021

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Typhoon Chanthu strengthened to a Category 5 system during Thursday which briefly had wind speeds of 165 knots or 305 km/h at the core, making this the strongest storm to date for 2021. The storm weakened slightly but regain strength a second time as a Category 5 storm. The storm has been labelled a "super typhoon".

The power of the storm is being attributed to its compact size and its passage over waters heated to 31C.

As at Thursday evening, the modified forecast models showed the storm making landfall across south east Taiwan although further updated models suggest that the storm may brush along the east coast of the island with possible landfall along the eastern coastline.

As shown on Google Earth Experimental 2021, the storm has potential to make landfall within proximity to the area as shown. The east coast of Taiwan is rugged with mountains. It is these mountains that will enhance rainfall and as such, rainfall and orographic influences will intensify the impact. The terrain is often cut with deep river valleys. Any landfalling typhoon within this area provides the added risk of flash flooding, sudden surges in rivers and landslides.

The east coast is more sparsely settled than the west coast which will help to lessen damage impacts however coming off the ocean as such, the storm will have the potential to cause significant damage to any community and infrastructure directly in its path.

The radar image from PAGASA, the Philippines weather service shows the entire storm and its compact eye at its closest approach to the country. A small eye is surrounded by intense bands of thunderstorms.

The storm has brushed the north east coast of the Philippines and now changes course more towards Taiwan where landfall is possible. The storm will lose some of its strength but will still be a significant storm as it approaches Taiwan.

The images of the storm are taken from:-

1 - MODIS (Terra) operated by NASA 10/9/2021.
2 - CIMSS.
3 - PAGASA 10/9/2021.
4 - The 3D images of south eastern Taiwan is from Google Earth Experimental 2021.

East coast low, rain, gales and cold – 24 August 2021 – Sydney to South Coast NSW.

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Following a recent warm spell that saw maximum temperatures reach up to 28.6C at Penrith on Sunday, weather conditions deteriorated rapidly after sunset Monday evening across coastal areas including Sydney.

It is known that some thunderstorm activity occurred in some parts of Sydney and to the south of Sydney however following the passage of the cold front, an east coast low developed during Tuesday that has brought some moderate to heavy rainfall and significant wind gusts.

Rainfall

For the 24 hours to 9 am Tuesday 24 August 2021, much of Sydney received between 24 and 37 mm. Such rainfall was relatively uniform across the city with the heaviest total of 37 mm falling within areas close to the airport.

Higher rainfall figures were recorded at the following locations for the same period:-

Illawarra

65 mm at Beaumont (The Cedars).
64 mm at Burrawaong.

Southern Tablelands

53 mm at Braidwood.

Central Tablelands

51 mm at Canobolas, Oberon and Orange.

There were also good rainfalls at Alectown (Central West) - 53 mm and at Nundle also 53 mm.

For the 24 hours to 9 am Wednesday 25 August 2021, some higher rainfall totals occurred around Sydney including:-

90 mm at Little Bay.
56 mm at San Souci.
54 mm at Randwick.

There were heavier rainfall totals within parts of the Illawarra / eastern parts of the southern tablelands including:-

83 mm at Robertson.
80 mm at Clover Hill.
79 mm at Macquarie Pass.
77 mm at East Kangaloon.
62 mm at Moss Vale.

Temperatures

Also noteworthy were the maximum daytime temperatures being significantly below average including 10.4C and 10.5C at Horsley Park and Badgerys Creek respectively, 11.5C at Observatory Hill Sydney and 12.8C at Penrith. This is a significant change and has resulted in the second coldest day this winter for much of Sydney (The coldest day occurred on June 10).

Peak wind gusts and gales

This was a significant feature of this system especially for exposed coastal locations within the Illawarra / Shoalhaven region of New South Wales but such high winds were limited to exposed coastal locations and fortunately such high winds did not penetrate too far inland.

Stronger damaging winds occurred at Albion Park (Southern Wollongong) where a gust of 102 km/h occurred at 5.02 pm. Further, a gust of 113 km/h occurred at 6 pm and between 6.58 pm and 7.05 pm, three peak wind gusts of 120 km/h occurred.

At nearby Kiama to the south, a single wind gust of 130 km/h occurred at 7.14 pm being the strongest wind gust recorded from this event.

Point Perpendicular

At Point Perpendicular, the weather station recorded a peak gust of 124 km/h at 4.45 pm, at 7.05 and again at 7.10 pm. A closer review of this weather station shows numerous peak wind gusts of between 107 km/h and 124 km/h between 4 pm and 12 midnight peaking at 124 km/h.

The table highlighted in blue shows conditions between 4 pm and 12 midnight and column 9 showing peak wind gusts is a standout. (Source BOM Point Perpendicular Weather station 24/8/2021).

The weather station has recorded the most sustained intense winds from this system partly due to its exposure and location to such winds.

Such winds did not penetrate too far inland and other weather stations within vicinity to the coast within the region recorded the following:-

Ulludulla - A peak wind gust of 98 km/h occurred at 5.25 pm.
Nowra - A peak wind gust of 89 km/h occurred at 7 pm.

Such winds have caused damage in affected areas with trees being blown down and damage to property evident including downed power lines and power loss. A cleanup is now required in affected regions.

This system is now moving away from the coast allowing for a rapid improvement in weather conditions over coming days.

Late August Warmth and cold wet outbreak SE Australia – 21 to 25 August 2021

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A recent burst of early season spring warmth is now coming to a close with a significant cold front and cold outbreak approaching south east Australia.

As shown on the Himawari satellite image of southern Australia Sunday morning 22/8/2021, most of southern Australia is generally under clear skies which is allowing a burst of warm air to filter down from the north and Central Australia. As shown, a strong cold front is now visible approaching Victoria and South Australia from the west which will cross the southern part of Australia during the latter stages of Sunday, Monday and into Tuesday.

It appears that this will be a significant weather event.

Ahead of the change, warm winds and weather conditions prevail and forecasts are being made for maximum temperatures to reach up to 27C across Sydney on both Sunday and Monday ahead of the change.

These are not record daytime maximum temperatures for August for the Sydney metropolitan area because there have been warmer August days in previous years such as:-

Sydney Olympic Park - The maximum temperature reached 27.9C on August 27 2007.
Penrith Lakes - The maximum temperature reached 27.5C on August 11 2002.
Parramatta (Masons Drive) - The maximum temperature reached 30.6C on August 26 and 30C on August 31 1995.
Prospect - It reached 29C on 4 days during August 1995.

Notwithstanding this, the current event is still significant as such warm events are relatively rare for the month of August.

Even across New South Wales, the maximum forecast temperatures for Sunday include:-

Tibooburra - 30C.
Brewarrina - 31C.
Wilcannia - 29C.

Further south, 21C is forecast for Wagga Wagga and Albury.

However, a major cold front sweeping across southern Australia will conclude the warmth. A rain band will accompany the change and there is even the potential for embedded thunderstorms.

Low level snowfall will accompany the change across higher elevations.

A feature of this event is that once the change reaches the New South Wales Coast, there is evidence to suggest that a short lived east coast low will form during Tuesday. As such, rainfall totals are suggested to be more significant with forecasts being made for 50 mm to 75 mm for some coastal locations.

In Sydney, Maximum temperatures will go from around 27C on Sunday to around 14C to 15C by Tuesday. Sydney should experience its heaviest rainfall for winter during this event (Between 6 to 15 mm for Monday (Latter part of the day) then 40 mm to 60 mm during Tuesday) with the development of an east coast low.

Conditions will begin to settle down on Wednesday.

This event will show that winter for 2021 is still with us notwithstanding the warmth that is occurring Sunday and into Monday.

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