Author Topic: Heavy rainfall & flooding in Sydney  (Read 11478 times)

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Stephen

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Heavy rainfall & flooding in Sydney
« on: 17 April 2006, 08:11:53 PM »
Hi everyone! My name is Stephen & I run an official rainfall station at North Turramurra for the Bureau of Meteorology, & an unofficial weather station, recording almost every other element possible. I am in Yr 10 at St Ives High School in Sydney's North.

I just wanted to start off by beginning a new topic on severe rainfall events in Sydney, of which there have not been many of recently. Sydney's main sources of significant rainfall events are generally:-

a) East Coast Low Pressure System's
b) Thunderstorms
c) NW cloudbands
d) Low pressure trough's, generally feeding moist NE winds
e) Cold fronts, although rarely producing severe rainfall events
f) Moist onshore winds

Significant rainfall events over the last 12 months or so have been quite rare, as in the last 2 years, Sydney has recorded less than 1000mm. To think that Innisfail recorded over 1000mm during March is amazing! Our annual average is over 1200mm. However, there have been some severe rainfall occasions. Here are some Northern Sydney events:-

a) March 22-23 2005: East Coast Low, with 73mm falling in Sydney & 82mm at Turramurra (my rainfall recordings began in May 2005)
12mm fell in just 30 minutes at Sydney between 5:30pm & 6pm on March 22nd. The Sydney Basin Rainfall Image of the event is attached.

b) May 12 2005: Heavy localized showers, especially in Northern Sydney. 53mm fell at Turramurra, with 48mm falling at North Turramurra (my station), 46mm at St Ives & 35mm at Pymble. These rainfalls were within less than 3 hours. They were generated by moist onshore Easterly winds.

c) June 29- July 1st 2005: Widespread rainfall across Sydney & NSW. Very wet conditions, generated by a low pressure trough, feeding moist NE winds. On July 1st, rainfall accumulations were: 88mm at Chatswood, 87mm at Royal National Park, 84mm at Darkes Forest & 78mm at Wedderburn. Across Northern Sydney, 58mm fell at Turramurra, 57mm at Pymble, 54mm at North Turramurra and 62mm at Avalon. Falls were typically much lighter out west, with just 9mm falling at Windsor and 10mm at Box Hill. 56mm fell in Sydney.

d) November 29 2005: Heavy rainfall from a severe thunderstorm in Western & Northern Sydney. 46mm at Turramurra, and 38mm at North Turramurra. Falls were within just one hour.

e) January 16 2006: Heavy rainfall from severe thunderstorms in NE Sydney. 40mm in Sydney, 72mm at Avalon. Major contrasts, with just 6mm falling at North Turramurra.

f) February 26 2006: The Sydney Flash Flooding event. Mentioned on this website by Jimmy Deguara! Major Severe thunderstorms beginning from the south and west & gradually moved NE. 90mm fell at Box Hill, 94mm at Glenmore Park, but a mammoth 101mm at Avalon once again. 63mm at North Turramurra, 78mm at Turramurra, 57mm at St Ives & 55mm at Pymble. Estimates show that approximately 24mm fell in just 15 minutes at North Turramurra. Flood damage reported in Hornsby, with some flash flooding.

g) March 29th 2006: The March exception. Most of Sydney experiencing very dry conditions during March. Just 28mm falling at North Turramurra during the month. However, on this day 40mm fell at Avalon once again, from moderate- heavy coastal showers.

Unfortunately, I'm on my laptop at the moment, so I don't have access to my archives of radar images or Sydney Basin Rainfall images that I can send as attachments. However, I did find the March 23rd 2005 rainfall image on the net, & have attached that. I'll send the images through my next article.
I think I need to go storm- chasing next summer to see some severe thunderstorm events producing mammoth rainfall totals... much larger than the ones mentioned here!

Hope you found this interesting...!

Stephen




« Last Edit: 24 April 2006, 06:16:56 AM by Stephen »

Offline Jimmy Deguara

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Re: Heavy rainfall & flooding in Sydney
« Reply #1 on: 23 April 2006, 07:08:56 PM »
H Stephen,

This is a well documented coverage of the event. It was the most intense long duration rainfall event I had experienced for some time. I am located in northwest Sydney where 90mm plus rainfall occurred.

Regards,

Jimmy Deguara
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