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Above: Sydney radar images at hourly intervals
from 8pm EST Monday (10.00 UTC 12/05/03) to midnight EST this evening (14.00
UTC 13/05/03). The images from 8am to noon, when the heaviest rain was
falling, are paused for longer. BoM |
Upper air diagram (below) for
Sydney Airport showing the temperature and dew point traces for
6am and 3pm, and wind at 3pm. BoM
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Sydney (above) and Central and Illawarra Coast
(below) rainfall for the 24 hours to 9am. BoM
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Rain with several hours of torrential downpours ushered in five days of rain
with flooding and serious traffic dislocation to parts of Sydney, Wollongong
and the Gosford
area today. A weak trough lying close to the
coast brought deep, saturated northeasterlies off the Tasman onto the hills
and ridges of the Sydney Basin. With rough terrain providing
added uplift to an only modestly unstable atmosphere, some heavy falls resulted,
especially
on the windward slopes to the north and south of the city and near the Illawarra
Escarpment. Similar conditions continued through until Friday as a shallow
Low developed off the SE QLD coast and moved slowly down the NSW coast (see
reports on subsequent days).
The animated radar image at right shows how a conveyor belt of rain 50 to
80km wide and moving in from the northeast developed in the Sydney area before
midnight and continued for most of today.
The upper air diagram below the radar shows the temperature and humidity measured
by radiosonde balloons released at Sydney Airport around 6am (blue) and 3pm
(red). The righthand trace in each case is the temperature and the lefthand
trace the dew point; the smaller the gap between the two the moister it is.
The temperature scale is along the bottom of the chart and the brown temperature
lines slope
upwards and to the right. The air is virtually saturated
to around 400hPa or about 8km. The temperature traces are nearly parallel to
the grey line,
indicating
nearly neutral buoyancy, although there is some instability betwen 900 and
800hPa, or around 1 to 2km up. The 3pm wind arrows down the righthand side
of the chart are steadfastly northeast at around 20 knots all the way up to
400hPa.
Heavy rain began falling in the Gosford/Wyong area soon after midnight and
became torrential around dawn. Narara just north of Gosford recorded 42.2mm
between 6 and 7am and a total of 82mm in the 3 hours to 9am.
Light to moderate rain fell across much of Sydney through the night, saturating
the ground, washing debris from dry roads into drains and producing good flows
in most streams.
An area of very heavy rain then gave 30 to 60mm to Sydney's northern and western
suburbs between around 6 and 10am before intensifying and moving across Sydney's
southern suburbs between about 7.30am and midday. It continued moving down
the coast
to give
Wollongong the same treatment between about 11am and 3pm. With around 8km of
cloud above the rain it was an extraordinarily dark morning, illuminated by
sporadic lightning.
Some of the more
significant 3-hourly rain totals were:
| |
6am to 9am |
9am to noon |
noon to 3pm |
9 hour total |
| Turramurra |
38 |
28 |
4 |
62 |
| Homebush |
28 |
23 |
4 |
55 |
| Strathfield |
24 |
22 |
8 |
54 |
| Peakhurst |
13 |
52 |
14 |
79 |
| Marrickville |
10 |
37 |
15 |
62 |
| Potts Hill |
26 |
22 |
7 |
55 |
| Sydney Observatory Hill |
18 |
15 |
10 |
43 |
| Holsworthy |
11 |
21 |
18 |
50 |
| Canterbury |
15 |
18 |
10 |
43 |
| Little Bay |
11 |
36 |
20 |
67 |
| Sans Souci |
26 |
70 |
14 |
110 |
| Cronulla South |
27 |
57 |
30 |
114 |
| Royal National Park |
25 |
93 |
22 |
140 |
| Lucas Heights |
14 |
35 |
8 |
57 |
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9am to noon |
noon to 3pm |
3pm to 6pm |
9 hour total |
| Scarborough |
51 |
28 |
17 |
96 |
| Wollongong AWS |
32 |
42 |
12 |
86 |
| Cringilla |
44 |
26 |
18 |
88 |
| Albion Park |
24 |
41 |
11 |
76 |
Further details of particularly heavy falls are given in the Downpours box
below.
In Sydney, chaos consumed the morning peak hour with radio traffic reports
barely able to keep up with the flow of traffic disabilities. Blacked out
traffic signals, stalled and crashed cars, and flash flooding made the
worse by drains and waterways clogged with rubbish after
many dry months lengthened commutes to 3 or 4 times the normal.
The situation was worst in the southern suburbs. At North Bexley, two
people had to be helicoptered from the roofs of their submerged cars. A
number of motorists were trapped when water flooded the M5 East motorway
after plastic sheeting blocked a drain. An intensive care ambulance was
stuck in rising floodwaters on Port Hacking Road, Sutherland.
Power was lost to 50,000 homes in southern Sydney and 2,000 more on the
Central Coast. Emergency services were kept busy with more than 600 calls
to clean up homes, schools and businesses after local flooding and to deal
with
fires
started
by lightning
strikes.
In the Illawarra, feared devastating flash flooding like that in 1998
from heavy rain on the escarpment failed to eventuate when winds maintained
a small
angle
to the cliffline. As a result, the heavy rain was more evenly spread with
much of the Wollongong area from Albion Park north recording between
60 and 90mm
during
the late
morning
and afternoon.
Lawrence
Hargrave
Drive between Clifton and Coalcliff was closed as was the adjacent main
Illawarra Railway due to feared landslides and earth movement.
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