Radar and lightning tracker animation every two hours from 8.50am yesterday to 12.50pm today, with a final frame at 3.20pm today. Weatherzone, BoM, Kattron.

NSW, QLD: Major flooding claims 3 lives, causes $25m+ damage

Up to 400mm of rain in six hours brought major flash flooding to the QLD Gold Coast today, while record falls in the Tweed, Brunswick and Richmond Valleys caused widespread main river flooding. Three people were drowned, while damage estimates are put at over $25m for home, motor vehicle and general claims, and a further $2.7m in repair to community infrastructure. Heavy rain and strong winds over a broader area of NSW and SE QLD caused widespread lighter damage and disruption, but delighted drought-suffering farmers, with many grain growers expecting their best winter crops in five years.

In SE QLD, the torrential rain closed Coolangatta Airport, triggered landslides, power blackouts and car crashes, interrupted the mobile phone network, inundated homes and stranded motorists. In NE NSW, hundreds of people were evacuated as flooding worsened. Ironically, this is one of the few parts of the state not in the grip of drought. From the Gold Coast to the Illawarra, strong winds brought down trees and caused roof and structural damage to houses, resulting in nearly 1,500 callouts for SES assistance. NE NSW was declared a natural disaster area, meaning that people living in the local government areas for Lismore, Byron, Tweed, Ballina, Richmond Valley and Kyogle will be eligible for disaster assistance measures.

The analysis at 10am today for 850hPa (about 1.4km above sea level) locates a band of strong convergence and deep moisture across NE NSW responsible for flood rainfall over the previous 24 hours. Weatherzone, BoM

Why it occurred

The surface chart at the top of this page gives little indication of the forces that generated the torrential rain, variously described as a 1 in 10 to 1 in 30-year flood event. The 10am surface chart shows a broad trough covering much of QLD and NSW with a specifically marked tighter trough right on the coast from Fraser Island to the NSW North Coast.

The main cause was the arrival over SA last Saturday of a trough or meander in the normally westerly upper air flow. During Sunday, the trough separated from the westerly flow and developed its own circulation, moving from Adelaide to SW QLD by Monday. In addition to transporting cold Southern Ocean air in the upper atmosphere across NSW and southern QLD, the upper circulation began dragging very moist air from the Coral Sea southwards over QLD and northern NSW.

Between Monday and Wednesday evening, this circulation (or upper low or cold pool) stalled over the NW NSW/SW QLD border area, but continued to draw increasingly moist, warm air down its eastern flank in the bottom few kilometres of the atmosphere. The combination of cold air aloft and the rotation in the system ensured widespread instability and uplift in the moist northerlies with widespread heavy rain the result.

From late yesterday afternoon to late this morning, a zone of strong convergence developed in the lower atmosphere, clearly visible in the 850hPa chart for 10am (). The strong northeasterlies east of 150°E converging into the northerlies west of 150°E have nowhere to go but up, enhancing the uplift in an area of deeply saturated air and concentrating heavy to torrential rain east of 150°E from the Gold Coast to the northern Hunter Valley.

Rainfall for the 24 hours to 9am for NSW above , and below for SE QLD , NE NSW and the NSW Mid North Coast . BoM

Rainfall

The map of NSW at left () shows that totals above 100mm for the 24 hours to 9am were general from the Gold Coast to the northern Hunter Valley. Totals of 50 to 100mm were widespread on the NSW North West Slopes and Plains. All totals of 50mm or more are listed in Wettest below and details of the heavier short duration falls are in Downpours.

The 24 hours to 9am period coincided with much of the heaviest rain, so that many new June records were set. Known records are listed in Records below, the most significant being Tweed Heads which, with 386.0mm, experienced its wettest day since records began in November 1886. Six stations had their wettest June day in over a century: Tweed Heads (386.0), Mullumbimby (287.0), Woodburn (275.6), Yamba (250.4), Dungog (132.0) and Gravesend (69.0).

The heaviest 24-hour recordings were all in a band from around Surfers Paradise through Coolangatta/Tweed Heads to Mullumbimby. The top official figures were Tweed Heads 386.0, Coolangatta Airport 369.0, Gold Coast Seaway 350.8, Nerang 346.0 and the Air Sea Rescue gauge 5km N of Surfers Paradise with 322.0. However, the flood warning network, where quality control is not assured, produced some significantly higher 24-hour totals. These included:

Nerang catchment, Gold Coast:
510 Carrara
497 Loder Creek Dam
480 Evandale
477 Biggera Creek Dam
411 Loder Creek
406 Boobegan Creek Lock
398 Bonogin Creek
393 Tallebudgera Creek Road
381 Coplicks Bridge
378 Oyster Creek

Tweed catchment, NSW:
418 Duranbah
344 Goonengerry

Brunswick catchment, NSW:
423 Middle Pocket
384 Chincogan
340 Mullumbimby Creek
323 Myocum

Wilsons catchment, NSW:
345 Repentance
344 Goonengerry

All of the Gold Coast falls over 400mm are within 7km of Surfers Paradise; Carrara is 7km WSW of Surfers Paradise. Duranbah is 14km S of Tweed Heads and Middle Pocket is halfway between Murwillumbah and Byron Bay.

The heaviest Gold Coast rain fell between about 3am and late morning with the highest totals in the Nerang catchment. For example, Carrara recorded 432mm and Evandale 403mm between 4 and 10am. The heaviest known hourly totals were 145mm at Carrara and 111 at Boobegan Creek Lock, both between 7 and 8am. The heaviest 3- hour totals were all between 6 and 9am, headed by Carrara 284, Boobegan Creek Lock 221 and Evandale 219mm. Coolangatta Airport registered 441mm between 2am and noon, its heaviest hour's rain being 97.8mm to 6.30am. Gold Coast Seaway recorded 408mm midnight to noon.

The situation was similar in the NSW Tweed and Brunswick catchments, where 3-hour totals to 9am were headed by Duranbah 237, Middle Pocket 165 and Chincogan 122mm. On the Wilsons River, which passes through Lismore, rain was more evenly spread through the 24 hours to 9am.

Flooding and weather

The radar animation () shows rain streaming south down the trough/convergence line. The southerly movement and relative narrowness of the rainband confined the very heavy falls to the coast or lower reaches of coastal river systems, substantially reducing the flooding that would have occurred had rain of this intensity fallen in main river headwaters. As the trough skewed offshore around midday, rain ceased on the Gold Coast and NSW North Coast, easing the threat of flooding just when emergency services were bracing for the worst.

Strong northeasterly winds were experienced along the coast in the tight pressure gradient between the trough and a 1037 high in the central Tasman. The highest average 24-hour wind speeds recorded in the nation to 9am were 49.9km/h at Newcastle Nobbys, 45.8 at Cape Byron, 44.6 at Cape Moreton and 43.0 at Norah Head. Top wind gusts were 109km/h at Cape Byron, 102 at Montague Island, 95 at Cape Moreton and 93 at Moss Vale. The winds whipped up heavy seas, with press reports of one wave reaching 10.65m off the Tweed Coast.

The flood and general weather situation in each catchment was as follows:

Brisbane: SES volunteers were required to deal with many water-damaged homes in Brisbane, Ipswich and Beaudesert. Most southeastern baysice suburbs of Brisbane recorded over 100mm in the 24 hours to 9am.

Gold Coast: Although there was widespread, severe flash flooding reported from almost every suburb, the coastal nature of the heaviest rain resulted in virtually no main river flooding. In the Nerang catchment, Tallebudgera Creek at Coplicks Bridge briefly reached major flood stage late morning. The only other flood stages reached were minor flooding in Teviot Brook at Boonah and Slacks Creek at Loganlea Road in the Logan-Albert catchment. Gold Coast City Council said the level of flooding and damage was the greatest since the 1974 floods.

A couple died when their ute was swept off the Birds Road bridge over the Coomera river NW of Nerang. Coolangatta Airport was closed with waist-deep water outside the terminal, stranding hundreds of passengers. Sixty-seven people were evacuated from their homes and many apartment basement car parks were flooded. About 120 residents were evacuated from a nursing home, the Miami caravan park and parts of Biggera Waters. The major Gold Coast shopping centre, Pacific Fair, was closed at 10.30am when the centre's carpark flooded. A house at Kirra collapsed, a retaining wall collapsed at Tugun and Palm Beach homes had to be sandbagged. Several properties atop Currumbin Hill were evacuated as they were considered unsafe because of possible landslides. Seven people were trapped in cars in different parts of the Gold Coast, and a woman had to be rescued from a caravan in Helensvale when trapped by rising water. The Gold Coast's four main theme parks were closed for the first time due to the weather. Flash flooding closed the Pacific Motorway, the main link between the Gold Coast and Brisbane, at Tallebudgera and many arterial roads throughout the Gold Coast were closed by flash flooding. Over 26,000 properties lost power when powerlines were brought down by uprooted trees and branches, car crashes into power poles and washed out underground cables. SES volunteers responded to more than 600 calls for help.

Tweed: The situation was similar in the Tweed Valley, where the only gauge to reach a flood stage was Murwillumbah which was above minor from late this morning to early Friday morning. Seventy-five nursing home residents were evacuated at Banora Point.

Brunswick: Following over 400mm in 24 hours at nearby Middle Pocket, Lacks Creek at Billinudgel peaked at 4.5 metres at 10am with major flooding. The main street of Billinudgel was evacuated with water knee-high. The Brunswick River at Mullumbimby Federation Bridge peaked at around 3.5 metres at 9am with moderate flooding. At Golden Beach, near Billinudgel, 100 people were evacuated from 50 homes that were inundated by sewage when floodwaters caused the sewerage plant to back-flood. Flash flooding at Byron Bay required sandbagging to protect homes, and a man drowned when apparently overwhelmed by flash flooding on his bicycle near Ewingsdale west of Byron Bay. The Pacific Highway was closed 3km north of Ballina.

Wilsons and Richmond: With 300 to 500mm falling across the northern Wilsons River catchment in the 48 hours to 9am, major flooding was expected in Lismore, the main city on the river, with moderate to major flooding in the lower Richmond River from Coraki to Woodburn. However, the sudden cessation of rain in the catchment around noon resulted in river levels upstream of Lismore peaking lower than expected, and a peak at Lismore of 10.2m around 10pm, the highest level since February 2001. The flood wave was also slow-moving between Lismore and Coraki, not reaching Woodburn until Saturday morning with minor flooding.

The last major floods in Lismore prompted the construction of an 11m levee around central parts of the city at a cost of $19m. It is due to be opened on 1 August, but received and passed an unexpected test today. The highest flood recorded was 13m in the 1950s, and when it was feared this morning that the Wilsons River may top the levee, evacuation of up to 6,000 people in the city was authorised. When it was realised early afternoon that the levee would hold (the peak was 70cm below the top), the evacuation plan was abandonned, though at a best estimate some 600 people were evacuated from parts of Lismore not protected by the levee. Five people were rescued from cars trapped in floodwater, including two in a stolen vehicle who were promptly arrested.

Orara and Clarence: Again reflecting the coastal nature of the rain, the only flooding in the large Clarence catchment was in the coastal Orara system. An average of 150mm was recorded across the Orara which peaked at 5.5m at Glenreagh around 3am Friday with minor flooding. Flash flooding at Yamba required sandbagging to protect homes. The Pacific Highway was closed by local flooding 10km N of Woolgoolga along with most other main roads in the area.

Bellinger: Minor flooding occurred at Thora from early this morning into Friday with a peak of 3.86m at 6pm. The river peaked at Bellingen at 3.7m, below minor. Most low-level bridges over the upper Bellinger were under water.

Macleay: Low level bridges at Bellbrook, Temagog, Turners Flat, Wittitrin and Moparrabah were covered.

Hastings: Minor flooding in the lower reaches around Kindee Bridge only. Kindee Bridge peaked at 4.5m around noon. Flash flooding entered some homes in Port Macquarie, and the Kendall and Upper Rollands Public Schools were closed when it was feared roads would be cut.

Manning: An average of 115mm fell across the catchment in the 24 hours to 9am with rain easing after noon. The river peaked at 5.9m at Wingham with minor flooding and 2.6m at Taree at midnight this evening with minor flooding.

Williams: Around 90mm fell in the 24 hours to 9am across the northern Hunter, causing minor flooding in the Williams system. Dungog peaked at 6.90m at 1pm with minor flooding. Mill Dam Falls peaked near 6.7m around 10pm.

Colo: Minor flooding is likely to have occurred in the Colo River at Putty on Friday, based on the Upper Colo River level which peaked near 8.4m on Friday morning.

Sydney: Minor wind damage resulted in 50 to 60 calls to SES, including a tree that crushed six cars at St Ives Primary School.

South Coast: A tree falling on powerlines in Wollongong about 2pm plunged 428 shops and offices along Crown Street, the main street, into darkness for 90 minutes. Other power outages occurred at Lake Heights and Wombarra. The Princes Highway was closed at Berry and Kembla Grange by flash flooding, while the Mt Ousley and Macquarie Pass roads also experienced flash flooding.

Namoi: With over 100mm falling in the lower Namoi Valley in the 30 hours to 8am, minor flooding occurred at Wee Waa (Glencoe) with a peak around 6.3m on Friday afternoon. The town of Pilliga was isolated, and Namoi SES had two helicopters supplying provisions to isolated rural properties and the Pilliga store.

Gwydir: Over 100mm of rain was recorded in the lower Gwydir Valley and the Horton River catchment in the 24 hours to 6am. The Horton peaked at Rider at 4.2m at 9am. The Gwydir peaked at Gravesend at 7.58m around 5pm with minor flooding and at Pallamallawa at 6.65m around 1am Friday with minor flooding. The Mehi River (an ana branch of the Gwydir) peaked at Moree at 5.85m in the early hours of Friday with minor flooding from local floodwater. The Gwydir at Yarraman Bridge peaked at 6.29m at 7.30am Friday with minor flooding. Tycannah Creek, just south of Moree, cut the Newell Highway and many local roads were blocked. The Newell was also cut by flooding between Dubbo and Gilgandra.

NT: Cold morning in the north

Overnight minima were unusually cool in the Top End this morning, especially in the west. Wave Hill's 2.4 was 9.2 below the average, while Victoria River Downs and Katherine were both 8.6 down on normal with minima of 3.6 and 5.4 respectively. Darwin's low of 16.1 was just 3.9 below average, but was still the coldest morning so far this year