Category Archives: Rain

precipitation in the form of droplets

Typhoon Chanthu brushes east coast of Taiwan – 12 September 2021

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Typhoon Chanthu has started to weaken as it tracks northwards brushing the east coast of Taiwan. The storm passed slightly further east of the island than initially expected and any direct landfall will no longer occur.

While the inner rainbands struck communities along the east coast, the eye has remained out to sea.

After producing wind gusts of at least 220 km/h across the north east coast of Luzon (Philippines), the storm turned further north than forecast and continues to weaken.

The storm has brought some very heavy rainfall and coupled with radar images from the Central Weather Bureau (Taiwan), there are weather stations that have recorded between 200 mm and 300 mm of rain with the heaviest totals to date including 226.5 mm at Lanyu High School and 216 mm at Lanyu. Rainfalls of 200 mm or more have been common along the eastern coastal strip of the island which would have contributed to flash flooding along rivers.

Most striking and with mountains reaching over 3,000 metres in height along a north / south spine of the island, very little rainfall is reaching the west coast. Rainfall is being intensified along the east coast due to orographic uplift. The mountains would also be contributing to a weakening of the storm.

This storm will now continue to travel in a northerly direction weakening further then dissipating altogether as it crosses over colder waters further to the north.

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.

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