WA: Ex-cyclone Isobel brings record rain, wind and flooding to the SE

Parts of SE WA recorded nearly half their annual rainfall, mostly today, as the remains of Tropical Cyclone Isobel interacted with an intense mid-latitude trough to bring widespread gales, flooding and damage. Flooding, stock losses, damaged roofs, downed trees, closed roads, blackouts and beach damage were widespread in an area around Esperance and westwards towards Ravensthorpe.

Tropical Cyclone Isobel weakened into a low pressure system after crossing the WA north coast near Pardoo soon after midday yesterday, but its massive moisture and instability began interacting with a southern trough advancing from the west as the ex-cyclone moved through mostly uninhabited desert country in the state's east overnight. By mid morning, the low was approaching the coast east of Esperance with a central pressure of 988hPa, similar to its intensity as a tropical cyclone. The satellite images below show cloud wrapping around the low and blasting the SE WA coast around Esperance with torrential rain and gale to storm force winds, which continued through the day as the low crossed the coast and moved very slowly away to the southeast.

BoM Manager of Weather Services in WA, Neil Bennett, said "While it is common for the remains of a tropical cyclone to cause heavy rain over inland parts of Western Australia it is quite exceptional to have it coincide with such a strong trough to the south". The storm was well forecast, with the Bureau issuing the first Severe Weather Warning for the area at 3pm WDT on Tuesday 2 January giving Emergency Services and the community plenty of notice before the strong winds and rain commenced.

Some long standing all-time one-day rainfall records fell as constant, heavy rain fell for up to 24 hours. The 134.1mm at Balladonia this morning eclipsed its previous record in 96 years of 77.5mm in 1945, while Ravensthorpe recorded 112.8mm on Friday morning (previous record in 101 years 102.9mm in 1939). The heaviest 24-hour total was at Esperance Airport which recorded 49mm to 9 this morning and a further estimated 172mm to 9am Friday, though power blackouts caused some losses of data that has not yet been recovered. Cheadanup, 120km W of Esperance, recorded a total of 204.2mm over the two days. Annual average rainfall in the area ranges from 400 to 600mm. For most stations with shorter records, it was the wettest day since the flood event of 6-7 January 1999.

This table from the Bureau of Meteorology indicates the highest known falls.

Ex-Isobel produced a band of 50 to 200mm plus rainfall through the east of WA during its passage, most evident in the weekly rainfall map to 9am Friday. Details of other heavy totals are in wettest for today and Friday. Also see downpours for details of heavy short-duration falls, especially at Esperance.

Gale to storm force winds accompanied the low, giving Esperance Airport its highest wind gust for January and highest daily wind average for any month. The gust of 111km/h recorded at the peak of the storm at 9pm was the highest for January in a 37-year history, but well below the all-time record of 152km/h on 28 May 1993. The 24-hour average wind speed to 9am Friday of 51.0km/h, however, made this the windiest day in the past 13 years during which daily wind run figures have been kept.

The effects of the storm were mostly felt in the Esperance to Ravensthorpe area. Fortunately, there were no reports of injuries or death.

• Damage: About 100 homes and some businesses reported damage, either wind damage to roofs or flood damage. Six houses were damaged by falling trees. Some families and about 25 campers were evacuated. The SES headquarters was flooded to thigh depth, and it has been announced that it will be replaced (at a new location) at a cost of $2m to $3m. A number of buildings on the TAFE campus were also flooded. SES responded to about 130 callouts, mostly to deal with local flooding, sandbagging and roof tarping. Damage to trees, powerlines and fencing was widespread, one farm reporting 100 trees blown down onto the driveway. Blackouts affected about 3000 properties in rural areas due to downed powerlines, while damaged generators in Esperance resulted in load sharing and rotational blackouts. Beach damage was reported along the coast, including 200m of the foreshore gouged away in Esperance where several boats broke their moorings and 1 sank in the Bandy Creek Boat Harbour. Bandy Creek Weir burst its banks, pushing tonnes of sand into the harbour grounding commercial fishing boats.
• Flooding: The area is relatively flat, with many short streams running into the Southern Ocean or lakes behind the coastline. Flooding therefore covered wide areas, submerging pastures and crops on many farms. The South Coast Highway was cut by a 40m washaway and bridge damage between Esperance and Ravensthorpe while gravel roads were impassable, stranding people on farms. The only way out of Esperance was the Coolgardie-Esperance Highway to the north.
• Farm losses: Large stock losses are expected, with estimates in excess of 100,000 sheep, with one property alone already reporting 500. The immediate problems have been drowning and hypothermia, with torrential rain and windchills today as low as 2C stressing recently-shorn sheep. The problem will be compounded over the next few days as much feed is submerged and farmers can't get feed onto vast, waterlogged paddocks. Hundreds of kilometres of fencing have been destroyed by flood-borne debris. Not yet known is the extent of topsoil erosion - little ground cover remains on many properties after the driest winter on record.
• Mining losses: BHP Billiton's Ravensthorpe nickel project, scheduled to go into service in 2008, remained at token levels, while its nickel mines at Mt. Keith and Leinster were closed as sodden ground prevented truck movements. Production at the company's Kalgoorlie smelter was disrupted. Minara's Murrin Murrin nickel mine east of Leonora closed down. BHP's iron ore operations at Port Hedland were temporarily halted, as were some Santos and Woodside Petroleum offshore oil operations.

Pastoralist Pam Halford, from Gibson, 25km NW of Esperance, summed up the feeling of locals in talking to ABC Rural: "There's quite a few rivers where there shouldn't be rivers, plus we've probably lost 100 prime lambs and well over 100 trees in our driveways. They've all been blown over and they're all across the driveway, both entrances to the farm, like one gum tree in the middle of the sheep yards, that went down and flattened the sheep yards. The super shed got sort of half blown away, the silo got flattened by another gum tree. We can't get on or off the farm at the moment but, you know, it's not desperate."

Aftermath: Aerial assessments of damage were conducted in the days following the storm, and suggest the damage bill will run into the millions of dollars. Enormous amounts of standing water and the many roads that are closed will prevent repair activities for days or weeks. These include:

• Stock losses, which were estimated on 18 January by the WA Department of Agriculture at 50,000, with some farmers losing up to 50% of their lambs.
• Making repairs to those parts of the 3,000km electricity network in the area that are not accessible at present due to boggy or inundated country. While main lines and the Esperance generators are now working, isolated farms will remain without power for days.
• Assessing and repairing the South Coast Highway, the main east-west route between Esperance and Ravensthorpe. Part of the bridge over the Oldfield River, 130km west of Esperance, has been washed away, and water needed to subside before damage could be assessed. The Young River bridge was also damaged. The road was likely to reopen to light traffic using detours about 12 or 13 January.
• Power was restored to all but 60 rural consumers by 8 January.
• An initial Agriculture Department phone survey of graziers on 8 January identified 30,000 stock as having been lost.
• Esperance's important tourism industry was adversely affected, with many people cancelling holiday arrangements in the town.
• Strong winds and high seas dislodged many seal pups from their nursery colonies. The Department of Environment and Conservation launched a rescue mission to find and return them along the coast of Esperance and east of Hopetoun.

On 8 January, the WA Government declared the Esperance region a disaster area, giving the community access to relief money when costs are known. The Shire of Esperance estimates the damage to road and rail networks alone will run into millions of dollars.

NSW, VIC: Murray River flow the lowest in a century. Figures released by River Murray Water show the river is the driest it has been since records began in 1892. 34 gigalitres of water flowed into the system in December, just one-tenth of the average, and the sixth month in a row of record low flows. The total inflow for 2006 was 1317 gigalitres, one-fifth of normal and eclipsing the previous record low of 1740 gigalitres in 1902 during the Federation drought.

NSW: Sydney catchment rain has little effect. Showers and thunderstorms over the past few days, especially on Monday and Tuesday, have had little effect on water levels in Sydney's dams. Figures released by the Sydney Catchment Authority today showed that average catchment rainfalls for the past week were: Warragamba 25mm, Upper Nepean 40mm, Woronora 75mm, Shoalhaven 25mm and Blue Mountains 55mm. However, much of this soaked into a parched catchment, with the total system capacity dropping by 0.1% to 36.3% during the week.

SA, VIC, TAS, QLD: High minimum and maximum temperatures. The minimum and maximum temperature anomaly charts show that today was unusually warm in the northerly airstream ahead of the WA trough, as well as in parts of Far North Queensland. Jervois and Watarrka set new high grass minimum temperature records, and Yulara had its second consecutive night of record January heat. On Cape York Peninsula, Kowanyama equalled its record January maximum temperature in the past 41 years (see records).

QLD: Storms cause power failures. Storms over the past two days have caused significant damage to electricity infrastructure in the central west, especially in the Stonehenge, Isisford, Barcaldine, Blackall, Jericho and Alpha areas. Over 500 properties lost power, some for several days. In one storm, seven power poles were knocked over. Three helicopters and crews were needed to repair damage. Longreach Airport again reported strong average winds in the 24 hours to 9 this morning (see records), while Namarah, 100km NE of St George, recorded an isolated 93mm in the 24 hours to 9am.