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.

Hurricane Ida – The aftermath – 3 September 2021

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The attached images of New Orleans acquired from NASA and dated 9 August and 31 August 2021 by the Suomi NPP satellite shows the stark impact caused by Hurricane Ida. Prior to the storm, the entire city of New Orleans is visible at night with the city centre, the brightest white generally centre of the image with Lake Pontchartrain to the north and the Mississippi River snaking its way through the centre.

Following the storm, most of New Orleans is without electricity and dark. The storm has caused immense damage and destruction to the infrastructure of the city. The city centre is lit again although most of the suburbs are in the dark.

Some of the lit areas are a result of backup electricity generation from diesel power units.

Instruments - Landsat 8-OLI.
Suomi NPP - VIIRS.

Source - Images acquired from NASA Earth Observatory (9 and 31 August 2021).

The storm has left at least 985,000 customers without power for days, weeks and even months. It appears another 33,000 customers are currently without power in nearby Mississippi.

Coupled with flooding, the situation is dire and the recovery will be difficult from such a storm. It is difficult to obtain readings from weather station as either such units have failed, were destroyed or stopped recording due to power loss as the storm passed over.

A weather station at Galliano (South Lafourche Airport) recorded a wind gust to 98 mp/h at 1.15 pm and another powerful gust of 95 mp/h at 3.55 pm (Converted to gusts of 157.6 km/h and 153 km/h but the station stopped recording thereafter. (Source NWS airport weather station Galliano).

There is reasonable evidence of a wind gust to 172 mp/h (Converted to 276.7 km/h) on a ship with an onboard weather station at Port Fourchon 100 km south of New Orleans. This is being reviewed but is credible as it was measured by NOAA Meteorological Officers. If confirmed, then this would be the highest wind gust known or confirmed from the storm.

Other intense wind gusts of 153 mp/h (Converted to 246 km/h) were reported at Lee Ville, 138 mp/h (converted to 222 km/h) at Dulac and 121 mp/h (Converted to 194.6 km/h) at Venie.

(Source NWS).

The storm appears to be the fifth strongest storm to make landfall in the United States and it is noted that landfall occurred 16 years to the day following Hurricane Katrina in 2005.

The storm became so strong so quickly because of the amount of warm water of 30C and 31C available that was situated along and off the coast of Louisiana. Unlike Hurricane Katrina which weakened a little before landfall in 2005, Hurricane Ida strengthened before landfall then slowed down after landfall which compounded the damage.

(Source Associated Press 2021, August 30 Hurricane Ida lashes Louisiana, knocks out New Orleans power)

Rainfall

With the loss of so many weather stations, it is difficult to ascertain how much rain fell within the area but a plot produced on the National Weather Service website for rainfall 30/8/2021 identifies likely rainfall for August 30 as being as high as 250 mm around New Orleans and 150 to 200 mm within immediate environs that the day.

Damage assessment

News images are providing detailed accounts of flooding and damage to infrastructure and buildings and it is far too early to ascertain damage costs or recovery times. News articles are reporting six fatalities at the time of writing which is expected to rise.

It is identified that most of the new levy banks constructed after Hurricane Katrina appear to have held up with only minor damage which will make search and rescue easier when compared to what occurred 16 years ago. Even though there is major flooding, it is less than what occurred during Hurricane Katrina.

I have been to New Orleans and remember being in this city on July 4 2002. I took note of the size of some of the levy banks along the Mississippi River and how low this city is when compared to surrounding water bodies. Without any of the levy banks, this city could never be built in this location due to such high flood risk.

Tropical storm

The storm was downgraded to a tropical storm following landfall which then tracked north east causing significant flooding to communities and other cities. The storm has passed over New York causing major flooding impacts in Manhattan and further state of emergencies. The north east United States has seen a wet summer from recent storms and the remnants of IDA has only added to the existing flooding that has occurred.

It is known that flash flooding and flooding has caused more than 40 fatalities.

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