Author Archives: Harley Pearman

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.

First 30C days for season before cold change Sydney – 11 to 12 September 2021

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During the weekend 11 and 12 September 2021, maximum daytime temperatures reached 30C for the first time this spring / summer season for certain areas of Sydney.

On Saturday 11 September 2021, it reached 30.4C at Penrith followed by 30.2C at the airport weather station. Most other parts of Sydney enjoyed maximum daytime temperatures of between 28C and 29.9C.

On Sunday, daytime temperatures were slightly higher and the first 30C temperatures for the season were more widespread across the city. This includes:-

Airport - 31.5C.
Penrith - 31.2C.
Bankstown - 30.3C.
Sydney Olympic Park - 30.2C.
City - 30.1C.

Where 30C was not reached, maximum temperatures reached at least 28C to 29.9C.

(Temperatures quoted are taken at 2.30 pm Sunday afternoon.)

Such temperatures are occurring ahead of another strong cold change crossing Victoria and New South Wales. Unlike the two previous changes, the change is not producing much rainfall. A significant rain event is not forecast however there is a strong temperature contrast before and after the change.

For example, at 1.30 pm on Sunday afternoon, it was only 14.4C at Albury, 16.9C at Moruya Airport, but 25C at Ulladulla. The change was approaching Ulladulla at the time.

Similar high temperatures were also recorded across the Hunter Valley, North West Slopes, and along the north coast of New South Wales.

Across Sydney, hot dry north west winds have filtered across the city and with clear skies, there has been much heating.

Following the cold change, temperatures will plunge and coastal showers will dominate for the next 2 to 3 days.

The Himawarri Satellite image of New South Wales of 2.10 pm Sunday afternoon shows the location of the change. It is a state of two halves with very warm dry conditions ahead of the change and the narrow cloud mass and cool to cold conditions following the change and cloud mass.

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.

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