Heavy rain impacts Sydney with flooding risks – Saturday 20 March 2021

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Heavy rain impacts Sydney with flooding risks - Saturday 20 March 2021

Between 9 am and 3.30 pm Saturday, Sydney has been drenched with some areas receiving substantial rainfall totals. During this period, I managed to take some photos of rising waters at a local park in Blacktown which provides an idea what is occurring at other localities across the city.

Heavy rain impacts Sydney with flooding risks - Saturday 20 March 2021
Heavy rain impacts Sydney with flooding risks - Saturday 20 March 2021
Heavy rain impacts Sydney with flooding risks - Saturday 20 March 2021

Such scenes would be occurring within any low lying area of the city and it is identified that minor flooding is now occurring at the North Richmond Pumping Station and a moderate flood peak has passed through the Colo River at Upper Colo.

Such rain appears to be easing across northern Sydney as the bulk of the rain system continues to move further south.

For the period 9 am to 3.30 pm, the following rainfall totals have been recorded across Sydney:-

Observatory Hill - 76 mm (Since Friday morning - 124 mm cumulative total).

Bankstown - 72 mm (Since Friday morning - 126 mm cumulative total).

Manly - 68 mm (Since Friday morning - 122 mm cumulative total).

Airport (Mascot) - 64 mm (Since Friday morning - 102 mm cumulative total).

Parramatta - 52 mm (Since Friday morning - 78 mm cumulative total).

Similar other totals have occurred throughout Sydney and more rainfall is expected.

Heavy rain impacts Sydney with flooding risks - Saturday 20 March 2021
Heavy rain impacts Sydney with flooding risks - Saturday 20 March 2021

Photos are attached in addition to a satellite photo of the cloud mass causing this event. It is noted that there are thunderstorms off the New South Wales North Coast from this event but these have generally remained offshore.

Heavy Rain and floods – Coastal New South Wales – 18 to 21 March 2021

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Heavy Rain and floods - Coastal New South Wales - 18 to 21 March 2021

A significant rain event is impacting coastal New South Wales within an area from the Mid North Coast southwards to Sydney. The worst affected regions include:-

  1. Mid North coast including towns and cities such as Coffs Harbour, Port Macquarie, Kempsey, Forster / Tuncurry.
  2. Hunter Valley including Nelson Bay, Newcastle and all towns and cities within the lower Hunter area.
  3. Central Coast (Gosford and Wyong).
  4. Sydney and Wollongong.
Heavy Rain and floods - Coastal New South Wales - 18 to 21 March 2021

In some instances, rainfall has been exceptional and significant flooding has / is occurring with damage including landslides being reported, rivers bursting their banks, roads being damaged and rescues occurring.

Major flooding has impacted the following localities:-

  1. Port Macquarie including Settlement Point and at nearby Wauchope where the Hastings River has peaked at almost 9 metres.
  2. Laurieton - (Mill Street).
  3. Taree - (At the time of writing, the Manning River was rising towards 6 metres in depth with flood levels exceeding the major flood level of 3.7 metres).
  4. Wingham - A major flood level peak of approximately 14 metres had been recorded.
  5. Gloucester - (Gloucester River) although the river levels are starting to fall.
  6. Patterson River (Gostwyck Bridge). At the time of writing, the river had just entered a major flood peak phase exceeding 12.2 metres in depth.

Moderate flooding has impacted the Nambucca River, North Haven, Dungog (Williams River) and Mill Dam Falls (William River) which is starting to approach major flood level as a flood peak moves downstream.

Heavy Rain and floods - Coastal New South Wales - 18 to 21 March 2021
Heavy Rain and floods - Coastal New South Wales - 18 to 21 March 2021

Closer to Sydney, rising waters are occurring at Upper Colo.

The focus of the main event has shifted southwards and for Saturday, the event is focused on the lower Hunter, Central Coast and Sydney.

Some of the rainfall over the past 5 days have been exceptional. In addition to the main rain event, there was a significant rain event across the Central West New South Wales on the 17/18 March 2021 with a number of towns within the affected region receiving between 50 mm and 86 mm including:-

Coonamble - 86 mm.

Quambone - 84 mm.

Keneline - 72 mm.

Trangie - 72 mm.

Dubbo - 65 mm.

Such falls are not common within the areas and towns named above but this event preceded the much stronger coastal event that is now occurring.

Heavy Rain and floods - Coastal New South Wales - 18 to 21 March 2021

Some coastal Lower Mid North Coast and Mid North Coast rainfall figures for the 24 hours to 18 March 2021 include:-

Nelson Bay - 150 mm.

Bungwahl and Wallis Lake - 142 mm.

Coffs Harbour - 50 to 97 mm although the heavier falls occurred closer to the hills to the west and north of the city.

On the 19 March 2021, rainfall intensities increased significantly which included:-

Coffs Harbour - 94 to 120 mm with 120 mm falling at Boambee.

Aldavilla (Macleay River) - 262 mm.

Upper Rollands Plan - 258.

Mt Seaview - 242 mm.

Utungun - 239 mm.

Kempsey - 226 mm.

Bowraville - 210 mm.

Nelson Bay - 202 mm.

Boonanghi - 196 mm.

Almost any town or locality has been drenched with such high rainfall totals. Very little of this is penetrating inland as such high rainfall totals decline sharply further west. The ranges of the Great Dividing Range is acting as an effective barrier and keeping this rain coastal.

Heavy Rain and floods - Coastal New South Wales - 18 to 21 March 2021
Heavy Rain and floods - Coastal New South Wales - 18 to 21 March 2021

For the 24 hours to 9 am 20 March 2021, some exceptional rainfall totals include:-

Logans Crossing - 362 mm.

Lake Cathie - 317 mm.

Laurieton - 309 mm.

Karee Island - 298 mm.

Wauchope (Bain Street) - 281 mm.

Utungun - 242 mm.

The Lower Mid North Coast is worst affected.

The Central Coast for the 24 hours to 9 am 19 March 2021

The heaviest falls include:-

Wangi Bowling Club - 149 mm.

Wyee - 142 mm.

Koolewong - 118 mm.

Sydney Metropolitan Area

This rainfall has reached Sydney with some significant falls occurring including:-

For 24 hours to 9 am 19 March 2021.

Lidcombe - 73 mm.

Richmond - 66 mm

Hornsby - 65 mm.

The highest fall was 86 mm just west of Barranjoey Head.

For 24 hours to 9 am 20 March 2021.

Bowgowlah Heights - 67 mm.

Chatswood - 64 mm.

Hornsby - 60 mm.

Where I live, at least 96 mm has fallen in the 2 days.

Heavy Rain and floods - Coastal New South Wales - 18 to 21 March 2021
Heavy Rain and floods - Coastal New South Wales - 18 to 21 March 2021

South of Sydney

An isolated fall of 151 mm fell at Macquarie Pass and 146 mm fell at Clover Hill south of Sydney but west of Wollongong for the 24 hours till 9 am 19/3/2021.

Across Sydney, already saturated areas and catchments will continue to receive more rainfall over coming hours leading to possible flooding.

A number of plots are provided showing the rainfall over the past 5 days taken from the Bureau of Meteorology site “Water and the Land”. The Himawari image attached is showing the cloud mass across Eastern New South Wales. Its interesting to note that convection is occurring off the coast which would indicate the presence of thunderstorms off the coast.

Heavy Rain and floods - Coastal New South Wales - 18 to 21 March 2021
Heavy Rain and floods - Coastal New South Wales - 18 to 21 March 2021

Strong Cold Front – Southern Australia – 14 March 2021

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Strong Cold Front - Southern Australia - 14 March 2021

A strong cold front has passed through southern Australia which is now progressing into north eastern New South Wales.

Ahead of this change, a warm to hot air mass surged southwards which resulted in temperatures reaching into the low to mid 30S however the air behind the change is relatively cool to cold.

This is a significant change due to the temperature changes that are occurring ahead and behind the change. For example, it reached 32.6C in Blacktown on Saturday but it has struggled to reach 20C on Sunday (Maximum being 20.2C).

Similar conditions are being felt across New South Wales ahead and behind the change.

A feature of this change is the large slow moving north west to south east cloud mass and rain band that marks the change. A closer look at this reveals a band of cloud that marks the presence of thunderstorms / embedded thunderstorms that is occurring at the leading edge of the rain band.

The change reached Western Sydney including Blacktown after 4 am Sunday morning. Some thunder was audible on the leading edge of the rain band between 4 am and 5 am with heavy showers. More general rain followed thereafter before easing into lighter showers.

Some rainfall figures include:-

Victoria (For the 24 hours to 9 am 14/3/2021)

42 mm at Mt Baw Baw.

40 mm at Mt Donna Buang.

20 to 29 mm across parts of the outer eastern suburbs of Melbourne in areas close to the Dandenong ranges.

New South Wales (For the 24 hours to 9 am 14/3/2021)

53 mm at Orange.

48 mm at Putty.

47 mm at Kulnurra (Jeavons).

46 mm at Wyee.

37 mm at Nowra.

30 mm at West Pennant Hills.

(For the 6 hours between 9 am and 3 pm)

The impacts are more noticeable as the system moves towards and into north east New South Wales. Rainfall figures for the 6 hours include:-

72 mm at Tangary Mountain.

60 mm at Elderslie.

49 mm at Tocal.

40 to 44 mm around Maitland.

The satellite photo from Himwari clearly shows the cloud mass that features this change with cumulonimbus clouds visible on its leading edge. The radar image of Sydney early Sunday morning shows the structure of the change with heavier rain evident on its leading edge with the change encroaching onto the Hunter Valley by 8 am.

Strong Cold Front - Southern Australia - 14 March 2021
Strong Cold Front - Southern Australia - 14 March 2021

The photo attached is showing one of the heavier showers that occurred Sunday morning at Blacktown.

Strong Cold Front - Southern Australia - 14 March 2021
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