Western Australia Tropical Cyclone Season Summary 2006-07

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Season Overview

There were just three tropical cyclones in the Perth TCWC area of responsibility George, Jacob and Kara, all of which occurred off the northwest coast during March. Of these only George had a direct wind impact to land areas crossing the coast near Port Hedland as a category 5 cyclone and causing extensive damage along its track. There were three deaths attributed to the impact of George. Just two days later Jacob crossed the coast in a similar location but as a tropical low. George, Jacob and Kara were all severe tropical cyclones, George reaching category 5 intensity, Jacob category 3, and Kara category 4. Although not causing a direct impact to land areas, the threat of Jacob and Kara did cause a significant economic impact by disrupting mining and offshore industry activities.

In addition in early January a tropical low was named Isobel operationally but was later downgraded to a tropical low during the reanalysis. It combined with a strong mid-latitude trough to cause heavy rain and flooding in the Esperance region.

Details of each Tropical Cyclone in the northwest Australian region 2006-07

Tropical Low 'Isobel' and the Esperance Rain Event30 December 2006 - 5 January 2007

A tropical low formed south of the Indonesian archipelago on 30 December 2006 and moved initially eastwards then took a general southerly track from 2 January 2007 weakening to the north of Port Hedland on near the Northwest coast on 3 January. On the 2nd the low was upgraded to cyclone intensity operationally and named 'Isobel' but the post-analysis indicates that the low did not reach tropical cyclone intensity. The most significant impact was economic from loss of productivity caused by the disruption to mining and offshore drilling operations and by the temporary closure of the port at Port Hedland.

Tropical moisture associated with the tropical low interacted with a remarkably deep mid-latitude trough resulting in heavy rain across the Goldfields, Eucla and South East Coastal Districts. The heaviest rainfall was near Esperance were flooding caused major damage to port facilities in particular.

For more details see full pdf report (0.3MB).

Severe Tropical Cyclone George 3-12 March 2007

Severe Tropical Cyclone (TC) George was both very intense and physically large. George was the most destructive cyclone to affect Port Hedland since TC Joan in 1975.

TC George formed on 3 March in the Joseph Bonaparte Gulf. It weakened back to a tropical low as it tracked westwards across the northern Kimberley and then re-intensified shortly after moving offshore into the Indian Ocean on 5 March. George intensified to a Severe Tropical Cyclone (Category 3) on the evening of 7 March and reached Category 5 as it approached the coast. It was still at its maximum intensity when it crossed the coast 50 km northeast of Port Hedland at 10 pm Western Daylight Savings Time (WDT) on Thursday 8 March.

The wind impact was greatest between Wallal and Whim Creek. A 10-minute mean wind of 194 km/h, equivalent to wind gusts of approximately 275 km/h, was recorded offshore at Bedout Island. At Port Hedland Airport, gusts of 154 km/h were recorded around 11 pm WDT prior to equipment failure. It is likely that stronger winds were experienced around midnight, on the outer edge of the band of maximum winds.

Winds decreased markedly as the system tracked inland overnight however George is estimated to have continued to produce "very destructive winds" (Category 3 or higher intensity) until just after 6 am WDT 9 March, at which time it was approximately 115 km south southeast of Port Hedland.

TC George produced large amounts of rain in the northern Kimberley and the Northern Territory earlier in its lifecycle. Upon approaching the Pilbara coast, substantial (but not exceptional) falls occurred. A lack of previous rainfall and the steady movement of George prevented significant flooding.

Reported impacts include three fatalities and numerous injuries at locations south of Port Hedland. Less than two per cent of buildings in the greater Port Hedland area (i.e. including South Hedland) sustained structural damage (Cyclone Testing Station, School of Engineering, James Cook University Queensland, (CTS) 2007a). The majority of damaged buildings were later identified as having weaknesses due to poor maintenance and it is notable that the majority of housing stock withstood the wind gusts, which were estimated to have reached around 200 km/h. The Bureau's Port Hedland radar dome sustained damage.

For more details see full report.

Severe Tropical Cyclone Jacob, 3-12 March 2007

A low formed well northwest of the Kimberley early in March and moved steadily westwards eventually reaching cyclone intensity at 06/18UTC. Cyclone advices were issued for Christmas Island on 7 March as Jacob moved to the northwest but were cancelled as the system recurved to the southeast on the 8th. Jacob reached category three intensity late on the 9th but weakened the following day under moderate northeasterly shear. Jacob continued its southeast then east southeast track eventually crossing the coast just east of Port Hedland as a tropical low on the morning of the 12th. Coincidentally this was almost the same point at which category five George crossed only two days before.

Although Jacob weakened before impacting the coast, the threat of a second cyclone put communities on high alert and hampered recovery operations following TC George. In addition there was an economic impact due to loss of production from oil and gas facilities and closure of port operations. Arterial roads were closed through eastern and central inland parts of the Pilbara because of heavy rain exacerbated by rainfall associated with TC George just a few days earlier.

For more details see full pdf report (0.93MB).

Severe Tropical Cyclone Kara, 23-30 March 2007

A low moved off the West Kimberley coast and developed reaching cyclone intensity about 465 km north northwest of Port Hedland at 25/06UTC as it tracked to the west. The midget system then rapidly developed to category four intensity by 26/06UTC and recurved to the east southeast. It remained at that intensity for 24 hours before rapidly weakening to a low by 28/00UTC near the east Pilbara coast at 80 Mile Beach.

Although communities were placed on alert, there was no reported wind impact or damage on the coast. Offshore oil and gas facilities were evacuated and there was likely to be considerable economic impact due to lost production.

For more details see full pdf report (0.98MB).

Tracks of tropical cyclones, 2006-07.

Season tracks 2006/07