 |
 Radar
and lightning animation hourly from 6pm Saturday to 11pm this evening
shows
the heavy localised concentration of showers about the Illawarra Escarpment
for most of the period, and its excursion into southwestern Sydney during
the afternoon. Weatherzone |
 |
 Meso-LAPS
Surface wind and temperature analysis at 10pm Saturday. Note the marked
convergence line between SE and E winds just north of 35°S, just
south of Wollongong. This line moved slowly north today triggering the
heaviest falls. Weatherzone
Silver, BoM
 |
 |
 Lower
atmosphere chart for 850hPa (around 1.4km) at 10am today. The contours
(°C) show
a weak upper thermal trough at this level up the NSW coast while the
green shading shows a narrow band of moisture coinciding with the convergence
line. COLA |
 |
 The
upper air diagram for Sydney airport for 6am (blue) and 3pm (red) shows
nearly
saturated air up to 500hPa (about 18,000 feet), with fresh southeasterlies
in the lowest few thousand feet feeding more moisture in from the Tasman
Sea. The curved grey line sloping upwards and to the left shows the temperature
that saturated air would need to be to remain in neutral buoyancy. As the
temperature traces (righthand red and blue lines) are to the left of this
and colder, the air can be seen to be slightly unstable all the way up
to 300hPa. BoM |
 |
24 hour rainfall totals to 9am today (above  )
and Monday (below  ). BoM |
 |
 Torrential
showers bring flash flooding to Sydney
and
Illawarra
A nearly continuous stream of heavy showers brought from 100 to over
200mm of rain and widespread flash flooding from Wollongong to the southwestern
suburbs of Sydney today.
The rain and flash flooding resulted from a classic alignment
of events that regularly but infrequently brings torrential rain to the Illawarra
Escarpment area. From late yesterday, a narrow band of very moist air was directed
onto the coast around Wollongong in a fairly strong east to southeasterly stream
, .
The escarpment behind Wollongong rises to a height of almost 400m within a few
kilometres of the coast, adding rapid uplift to the onshore stream. At the
same time, a weak upper trough with cooler temperatures aloft developed up
the coast
providing deep marginal instability. The trigger for the heavy rain was a zone
of wind convergence at
the surface and in the lower atmosphere. This convergence line formed south
of Wollongong mid evening Saturday and moved slowly north over the next 12
hours or so, generating thunderstorms off the Illawarra coast for several hours
in the early morning, and producing heavy rain from around Wollongong into
the southern and southwestern suburbs of Sydney .
Several convergence lines reformed in the area during the remainder of the
day leading to renewed heavy
showers.
The distribution of the rainfall over the two rain days ended 9am today and
Monday is shown in and .
The heaviest falls on both days were on the Illawarra Escarpment north of Wollongong.
Darkes Forest (Kintyre), 20km north of Wollongong, recorded the national top
total to 9 this morning of 130mm and followed this up with a further 119.4
to 9am Monday,
a 48 hour
total
of 249.4mm. The AWS on Bellambi Point, 10kmm north of Wollongong, recorded
59.6 to 9 this morning and the national high of 179.2 to 9am Monday for a 48
hour total of 238.8mm. The detailed record for Bellambi below
shows the rain falling through the day until about 7pm, with
occasional heavy bursts. Heavy totals from the flood warning rain network for
the 24 hours to 9 this morning were Balgownie 95, Kembla Grange 87, and Cringilla
and Keiraville 80, all suburbs of Wollongong.
The heaviest rain around Wollongong fell in two bursts, the first between
11 last night and 3 this morning. Wongawilli recorded 47mm 11pm to 1am, Kembla
Grange
58mm
midnight
to 2am, and Scarborough 39mm in the hour to 3am. Further heavy showers gave
Balgownie 70mm 7 to 11am and Wollongong City 56mm 7 to 10am.
The rain in the Illawarra led to flash flooding, flooded houses, landslips
and road and rail closures. Most of the 15 calls received by the SES in the
Illawarra were for water damage to houses due to blocked
guttering and drains. Rockfalls closed the northbound Princes Highway at Bombo
north of Kiama, and there were minor rockfalls at Mt Keira west of Wollongong.
Carters Way and Squires Lane at Fairy Meadow, just north of Wollongong, were
closed by flash flooding around 10.30am. About 10 road accidents were reported
around Wollongong, one closing Mt Ousley Road. Local flooding closed the Princes
Highway between Berry and Gerringong, and roads at Albion Park, Cringila and
Audley.
During the early afternoon, an area of heavy rain associated with the convergence
line moved slowly over Sydney's southwestern suburbs, then on into the western
suburbs during the late afternoon. The flood warning gauge at Liverpool registered
105mm between 1pm and 3pm, with the manually read Michael
Wenden Centre gauge in Liverpool reported 72mm between
9am
and 3pm. Other heavy falls were Cronulla South 44mm 6 to 8am, Woronora Dam
42mm 9am to midday, Bankstown Airport
42.4mm in the hour to 3pm, Potts Hill 52mm midday to 3pm, and Greystaynes 30mm
3 to 4pm.
The SES fielded about 85 calls, mostly from Bankstown, Liverpool and Holsworthy
to assist with flooded roads and houses and leaking roofs. The basement of
Liverpool Hospital was flooded about 5pm. Ambulances attended 55 road accidents
in the metropolitan area, about 2.5 times the norm, while police rescued 3
people from a flooded car in Bankstown around 2pm.
The rain continued into Monday (see separate report).
 Cold
morning in TAS
Clear skies under a high pressure system following the cold outbreak
of the past few days resulted in a chilly start to the day across southern
and central TAS. Tunnack,
20km SE of Oatlands, recorded the lowest minimum of -5.3 closely followed
by -5.2 at Liawenee on the Central Plateau. Bushy Park in the lower Derwent
Valley recorded -2.4, 8.7 below normal, while on the West Coast, Strahan
Airport, which is just behind the beach, reported in with a low of just 1.3. |
