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Saturday 11 March 2000

Today's weather extremes

 Flood peaks at Carnarvon WA
Heavy rain in SE WA and NSW/Qld  border country 02June00

Highest rainfall, 24 hours to 9am

129.0 Enngonia PO NSW
126.0 Barringun NSW
122.0 Bamaga Qld
104.0 Dum In Mirrie NT

Other high NSW/S Qld falls:
102.0 Trangie Res Stn NSW
89.6 Nyngan AP NSW
80.2 Thargomindah Qld
78.6 Brewarrina NSW
77.0 Kilcowera Qld
73.6 Kenebree Collerina NSW
72.9 Wellington Town NSW

Other high WA falls:
96.0 Mt Walton East
95.0 Cadjebut Fitzroy Crossing
91.0 Salmon Gums
86.0 Norseman PO
80.0 Warralackin Westonia
78.0 Esperance AP
76.4 Esperance Downs Res Stn
76.0 Boyadup
72.1 Southern Cross AP

Levee banks protected Carnarvon WA from major flooding today as the Gascoyne River south of the town peaked at 7.53m at 5.30 this morning, dropped slightly, then rose to 7.57m with the high tide this afternoon. This level is 22cm higher than the 1980 flood, and the highest level reached since 1961. However, millions of dollars worth of damage are being caused to mango and banana plantations, livestock, fencing, roads and other infrastructure by the floodwaters. Several hundred of the town's 10,000 residents were evacuated. Most roads in the district, and in the Pilbara and Kimberley regions to the north, remain impassable or blocked by flooded streams.
Heavy bands of rain swept the WA Goldfields, SW Qld and northern NSW in the 24 hours to 9am

Meanwhile, former TC Steve crossed the WA southern coastline south of Balladonia late this afternoon, still with a central pressure of 993hPa. Overnight and this morning, the depression continued to dump 50 to 100mm on a swathe of country from the central wheat belt through the Goldfields to the south coast around Esperance. Road and rail links from the Goldfields to the coast have been submerged or damaged. The Coolgardie to Esperance Highway is impassable, while the Dalyup River bridge 30km west of Esperance on the South Coast Highway is closed with major structural damage. Later estimates placed the total damage bill from this year's storms in the Esperance Shire at $1.6m. The Coolgardie to Esperance railway is also closed by washaways near Norseman, where 81mm fell in 15 hours, and scoured track formation farther south at Salmon Gums. Mining operations in the Kalgoorlie-Boulder area were stopped by the rain.

Heavy rain continued to fall in NSW and southern Queensland today as a slow-moving trough system moved from central to northeastern NSW while gradually weakening. An area of 70 to 130mm of rain fell from SW Queensland to the NSW Central Tablelands overnight and this morning, producing minor flooding in the Warrego River from the Queensland border south.


Chart 1

 The exceptionally widespread and heavy inland rains were the product of a number of favourable weather patterns coinciding. These five charts show the situation at 11pm last night.

Chart 1 is the surface situation, with a marked trough from SW Qld to south of Sydney, and heavy rain shown for the previous 12 hours along the same axis.

Chart 2 shows the situation in the lower atmosphere at the 850hPa pressure level, or about 1.4km -- the red lines (temperature) show a thermal trough, or colder air, along the same axis, but farther to the west. The grey shading shows 90+% humidity, and the wind barbs show winds converging into the trough -- i.e. coming from the NNW in the west, but the NNE in the east. There is a strong wind shear or shift to SE winds along the trough.

Chart 3 is the situation in the middle atmosphere at the 500hPa or 6km level. The green lines show the thermal trough, while the brown area shows enhanced vorticity or spin associated with the upper low, which is marked out by the white pressure level contours.

Chart 4 shows the jet stream operating in the upper atmosphere. The jet picks up speed from around 80km/h over SW Qld to around 180km/h SE of Sydney (known as the entrance to the jet). This acceleration causes divergence of air in the upper levels, supports the convergence at lower levels, and assists the whole middle atmosphere to rise.

Chart 5 shows the satellite infrared cloud image, with lines showing the amount of upper divergence superimposed.

In summary, the NW to SE cloud and rain band was produced by ample humidity, good low level wind convergence, a strong jet entrance enhancing upper divergence, and a marked trough of colder upper air moving in from the west increasing instability.


Chart 2


Chart 3


Chart 4


Chart 5

 

Highest & Lowest Temps

Maximum Minimum
38.0 Eucla AP WA
38.0 Ceduna AP SA
38.0 Kyancutta SA
38.0 Nullarbor Roadhouse SA		 27.1 Centre Is NT
14.9 Mt Wellington Tas 4.0 Lake St Clair Tas

Greatest variations from normal

Maximum Minimum
+13.0
38.0 Eucla AP WA		 +8.5
19.0 Lake Eildon Vic
-10.0
23.0 Paynes Find WA		 -6.1
15.5 Boulia Qld
Other extreme readings
Rainfall:
Esperance AP WA: 47.2mm in 4h to 7am
Yeelirrie WA: 55mm in 15h to 6am
Laverton WA: 25mm in 6h to 3am
Mt Walton East WA: 34mm in 6h to 3am
Kalgoorlie WA: 27mm in 6h to 3am
Norseman PO WA: 81mm in 15h to 9am
Salmon Gums WA: 58mm in 9h to 6am
Dum In Mirrie NT: 104mm in 6h to 9am
Weipa AP Qld: 70mm in 2h to 5pm
Brewarrina NSW: 67mm in 18h to 9am
Trangie Res Stn NSW: 55mm in 6h to 9am, 33.4 in 2h to 8am.
Mudgee AP NSW: 71mm in 9h to 3pm, 53.8 in 5h to 1pm.
Gulgong NSW: 94mm in 24h to 3pm
Nullo Mtn NSW: 37mm in 6h to 3pm
Bathurst AP NSW: 37mm in 12h to 9am
Wellington Town NSW: 93mm in 24h to 3pm

Flood peaks:
Gascoyne at 9 Mile Bridge, Carnarvon WA: 7.57m during the afternoon with major flooding
Fitzroy at Fitzroy Crossing WA: 12.05m at 4.55pm
Paroo at Humeburn Qld: 3.95m early this morning with moderate flooding
Paroo at Wanaaring NSW: 2.5m during today from an earlier flood peak
Namoi at Duncan Junction NSW: 5.84m during the afternoon
Records set this day
Highest daily rainfall for March:
Esperance Downs Res Stn WA: 76.4mm