Topic: NSW rain events and East Coast Lows 25 - 31 May 2010

[Harley Pearman]

NSW rain events and East Coast Lows 25-31 May 2010

On Tuesday and Wednesday 25 and 26 May, a good rain event unfolded across Victoria and large areas of southern NSW. That event brought useful and good falls of rain to southern inland New South Wales including 24 mm at Albury - Wodonga and approximately 30 mm to Wagga Wagga. Good falls of 20 to 40 mm of rain occurred throughout this area.

The event contracted to the coast by Wednesday and a small east coast low developed off the coast of Sydney. This resulted in sustained rainfalls occurring along the coast anywhere from Sydney south to the New South Wales / Victoria state border.

In Sydney, solid rainfalls caused some nuisance but localised flash flooding and numerous traffic accidents. Driving home from work at Auburn, I noted some significant water ponding across the parklands at Mona Park. For the 24 hours 9 am to 9 am 26/27 May, rainfalls included 56 mm at Mona Vale, 55 mm at Oatley and 52 mm at Merrylands West. Generally rainfalls were between 16 mm at Richmond to 56 mm at Mona Vale. The rainfall plot for Sydney for this period from the BOM 27/5/2010 is provided below. The cumulative totals are higher given that some rainfall occurred prior to 9 am 26/5/2010.

Strong rainfalls also occurred south of Sydney including 90 mm at Batemans Bay as well as falls of 100 mm plus around Moruya (South Coast) as well as inland to the coastal ranges.

Models are currently showing a second east coast low for Sunday and Monday, 30 and 31 May and a second burst of strong rainfalls along the New South Wales South Coast, Illawarra and Sydney during this period. Weather models are also showing a second rain event for large areas of inland New South Wales for the 29 May especially for the slopes and plains of the state and northern Victoria.

Harley Pearman

[Harley Pearman]

East Coast Low for 29 to 31 May 2010

At 3.25 pm 28/5/2010, the Bureau of Meteorology has issued "A Significant Weather Media Release" for the New South Wales South Coast for gales and very heavy rain for Sunday. The statement indicates that the heavy rain is expected to extend to Sydney and the Central Coast by Sunday night and into Monday morning.

Looking at GFS rainfall models on the 0Z Run out to 96 hours (From 28 May to 1 June), the models suggest rainfalls of 125 mm on the NSW South Coast South of Nowra but north of Bega and 25 mm over Sydney. The Bureau of Meteorology charts suggests 50 to 80 mm rainfalls over Sydney Sunday night.

The amount of rain that falls will be determined by the final position of the low but all indications are, the area from the NSW Central Coast south to about Bega is at risk from this system in terms of heavy rain and wind.

Models suggest that the area from Wollongong to Bega should bear the brunt of the east coast low. The GFS suggests the east coast low forming on the New South Wales South Coast off Batemans Bay to Bega. The Bureau of Meteorology charts (Attached) suggests the east coast low close to Sydney by Sunday night.

The NSW South Coast has already seen significant rainfalls over the past 7 days including 140 mm at Eden, 103 mm at Batemans Bay, 92 mm at Ulladulla and 84 mm at Bega. Given that the ground is already wet, there is a risk of coastal flooding in low lying areas should this event unfold as suggested.   

The latest Bureau of Meteorology charts for Sunday and Monday 30 and 31 May are attached below.

Harley Pearman

[Harley Pearman]

Overnight rainfalls across southern NSW 29/5/2010

At midday Saturday, a low pressure cell sits over southern / south western New South Wales making its way east. Overnight the system has brought a second burst of worthwhile rainfalls to southern New South Wales and Northern Victoria. The rainfall follows on the heels of the rain event of 25/26 May. The falls are widespread in nature.

Some of the heaviest falls as per the BOM weather stations to 9 am 29/5/10 include 36 mm at Hunters Hill and Yackandandah (NE Victoria), 28 mm at a number of centres such as Albury Airport, Barham, Kerang, Kyabram, 27 mm at Batlow and 26 mm at Swan Hill. Generally falls of 10 to 40 mm has occurred across the region. Given the position of the low pressure cell, shower activity / rainfall activity is still occurring in the region and thus totals will increase further until the weather system moves further to the east.

Lighter falls have occurred over much of the state including Sydney but I have noted some isolated thunderstorm activity developing off the coast from Sydney and south towards the Victorian State border.


Harley Pearman

[Harley Pearman]

East Coast low off the NSW South Coast Sunday 30 May 2010

At 5.25 am Sunday morning, the low pressure cell that brought the rainfalls to southern inland New South Wales has crossed the New South Wales South Coast and is now developing into an east coast low. A band of rain is concentrated on the New South Wales South coast North of about Bega (although some in eastern Victoria as well) and south of Nowra. The main rain is situated south of the core of the low.

Heavy falls of rain has started to occur as shown in the attached radar image including rainfall totals. Current totals to 5 am 30/5/2010 include 53 mm at Mallacoota (Victoria) and 48 mm at Narooma. Falls of between 30 and 50 mm has already occurred on a stretch of coast between Mallacoota and Narooma.

Yesterday evening, a thunderstorm cell over Camden and Campbelltown (South West Sydney) brought up to 25 mm of rain in a short period of time.

There are severe weather alerts current for the New South Wales South Coast for Sunday.

The current radar image from Bureau of Meteorology Obtained via Weatherzone (30/5/2010) including rainfall totals is showing where the event is occurring. As the day progresses, the rainfall totals will increase.


Harley Pearman

[Colin Maitland]

Part of the severe weather warning from BOM for this event states

HEAVY RAIN, DESTRUCTIVE WINDS AND DAMAGING SURF ALONG PARTS OF THE SOUTHERN NSW COAST AND ADJACENT RANGES TODAY

A deep low pressure system lies off the NSW South Coast with several intense low centres embedded. One centre has just crossed the coast near Narooma with a destructive wind gust of 135 km/hr reported from nearby Montague Island. A second centre lies further offshore and is expected to move to the west and impact the South Coast later this morning with another period of destructive winds and this time heavy rain associated. Other centres are likely to behave similarly during the afternoon and evening and continue to affect the South Coast. Heavy rain and damaging winds will develop over eastern parts of the Southern Tablelands today. The system is then expected to slowly track northwards, affecting the Illawarra coast later in the day.

The precise position and movement of the low centres will determine the location of the heaviest rainfall and highest wind and seas, and this warning will be updated regularly as the system develops.

Winds are expected to average over 65 km/h in the South Coast and eastern parts of the Southern Tablelands today, and possibly over 90 km/h along the coastal fringe. Gales may extend to the Illawarra district later in the day, particularly in the south. Peak wind gusts will exceed 125 km/h, particularly near the coast.

Very heavy rain is expected to cause flash flooding today in the South Coast and eastern parts of the Southern Tablelands districts. Heavy rain may extend to the Illawarra district later in the day or evening.

Damaging surf conditions, with waves exceeding 5 metres in the surf zone, may produce significant beach erosion today along the South Coast, extending to the Illawarra later in the day or on Monday. Water levels above the highest astronomical tide of the year are possible.

[Harley Pearman]

Rainfalls for 30/5/2010

Significant rainfalls have been occurring on the New South wales South Coast and up until 9 am 30/5/2010, some big totals observed include Nimmitabel 86 mm, Mt Darragh 85 mm, Bemboka 62 mm and Perisher Valley 52 mm. Falls of 16 to 85 mm have been registered between Ulladulla and Bega.

Between 9 am and 3 pm, more heavy rainfalls have occurred in the same coastal stretch ranging from 11 mm to 69 mm. Nimmitabel has had another 69 mm and Bemboka 44 mm. Cumulative totals in some places have exceeded 100 mm such as 155 mm at Nimmitabel and 106 mm at Bemboka. There is a threat of local flooding as rainfalls continue (Rainfall totals sourced from BOM weather station sites 30/5/10).

Rainfalls are still continuing but it appears that some falls are now moving north toward the Illawarra region.

Sydney has experienced a partly cloudy / partly sunny day. Currently there is an increase in Cirrus and Cirrus stratus clouds over Sydney and from the hills of Bella Vista (Baulkham Hills), dense clouds are visible on the horizon to the south of Sydney.

Harley Pearman

[Harley Pearman]

Rainfalls for 31 May 2010 (Including wind observations for Montague Island Narooma)

Today rainfalls tapered off as the low moved North East and away from the east coast of New South Wales. However it has left minor flooding for the Snowy River and the Bega River. For the 24 hours to 9 am 31/5/10, significant rainfalls occurred in the hills behind Batemans Bay south to Bega. The highest included 140 mm at Nimmitabel - (Cumulative total to 224 mm), 111 mm at Bendethra and 105 mm at Mt Darragh - (Cumulative total to 190 mm). Falls of 50 to 100 mm were common. Moruya (Plumwood) had up to 97 mm, Brogo Dam 70 mm and Braidwood 69 mm.

The system dropped isolated 200 mm falls (Cumulative totals) on the New South Wales South Coast. Very little has fallen since 9 am. (Totals sourced from various weather stations in the BOM Network 31/5/2010).

Wind gusts at Montague Island off Narooma

As highlighted by Colin, a wind gust of 135 km/h occurred at Montague Island. Weather Station ID 069017 (BOM Weather data for Montague Island 31/5/2010) recorded the following winds between 4.39 am and 6.57 am 30/5/2010:-

4.39 am - Wind gust to 95 km/h with peak gusts to 106 km/h.
5.00 am - Wind gust to 96 km/h with peak gusts to 120 km/h.
6.13 am - Wind gust to 120 km/h with peak gust to 135 km/h.
6.31 am - Wind gust to 100 km/h with peak gust to 132 km/h.
6.39 am - Wind gust to 98 km/h with peak gust to 113 km/h.
6.57 am - Wind gust to 76 km/h with peak gust to 102 km/h.

This shows the intensity of the low at Montague Island off Narooma. Further wind gusts to 122 km/h occurred at 12.36 pm. Wind gusts exceeding 100 km/h occurred here again between 10.37 am and 1.16 pm (30/5/10). Sustained winds of 100 km/h occurred between 12.36 pm and 12.58 pm. Finally another burst of 100 km/h winds occurred here between 8 pm and 9 pm. The East Coast low was intense off Narooma (South Coast New South Wales).
 
Sydney

Here in Sydney, a burst of shower activity occurred early in the day, followed by further shower activity which is now easing. Constant scattered shower activity was common right across the metropolitan area. The east coast low currently well to the east of Sydney did not bring severe damaging weather but did bring with it some wind and constant shower activity. I took two photos from the car park in Susan Street Auburn to highlight typical conditions for the day (Attached below). With the low east of Sydney, conditions varied from sunshine to showers, some briefly heavy at times.

Rainfall across Sydney ranged from 4 mm to 16 mm to 9 am and 1 mm to 18 mm between 9 am and 6 pm. An isolated fall of 28 mm fell at Camden in South West Sydney. Conditions should now settle as the system moves away from Australia's East Coast although shower activity should continue.


Harley Pearman