The 2010–11 Australian region cyclone season was a near average tropical cyclone season, with eleven tropical cyclones forming compared to an average of 12. The season was also the costliest recorded in the Australian region basin, with a total of $3.62 billion (2011 USD) in damages, mostly from the destructive Cyclone Yasi. The season began on 1 November 2010 and ended on 30 April 2011, although the first tropical cyclone formed on 28 October. The Australian region is defined as being to the south of the equator, between the 90th meridian east and 160th meridian east. Tropical cyclones in this area are monitored by five Tropical Cyclone Warning Centres (TCWC's): Jakarta, Port Moresby, Perth, Darwin, and Brisbane, each of which have the power to name a tropical cyclone. The TCWC's in Perth, Darwin, and Brisbane are run by the Bureau of Meteorology, who designate significant tropical lows with a number and the U suffix. The Joint Typhoon Warning Center also issues unofficial warnings for the region, designating significant tropical cyclones with the "S" suffix when they form west of 135°E, and the "P" suffix when they form east of 135°E. __TOC__
Seasonal forecasts TSR forecastsDate Tropicalstorms Severe Tropicalcyclones Landfallingcyclones ACE Ref Average (1975/76–2009/10) 10.5 5.5 4.5 79 5 May 2010 9.3 4.9 4 – 6 July 2010 12.5 6.7 5.2 – 6 September 2010 15.1 8.1 6.1 108 9 November 2010 15.4 8.3 6.2 111 6 December 2010 15.5 8.3 6.2 111 Region Average Chance ofAbove average Predictedactivity Actual activity Ref Whole 12 98% 20–22 10 Western 7 93% 11–12 6 North-Western 4 67% 5 5 Northern 6 75% 7–8 0 Eastern 4 87% 6–7 4 ForecastCenter Tropicallows Tropicalcyclones Severe tropicalcyclones Ref Actual activity: BoM 28 10 5 Actual activity: JTWC 13 13 5
Ahead of the cyclone season, the Bureau of Meteorology (BoM), the New Zealand National Institute of Water and Atmospheric Research (NIWA) and various other Pacific Meteorological services, all contributed towards the Island Climate Update tropical cyclone outlook that was released during October 2010. The outlook took into account the moderate-strong La Niña conditions that had been observed across the Pacific and analogue seasons that had La Niña conditions occurring during the season. The outlook called for a normal or above average number of tropical cyclone occurring during the season, with nine to twelve named tropical cyclones, to occur between 135°E and 120°W compared to an average of nine. At least three of the tropical cyclones were expected to become category 3 severe tropical cyclones, while one was expected to become a category 4 severe tropical cyclone. In addition to contributing towards the Island Climate Update outlook, the BoM issued seven seasonal forecasts during October 2010, for the Australian region and the Southern Pacific with each forecast covering the whole tropical cyclone year. Each forecast issued took into account the La Niña conditions that had developed over the region and were forecasted to persist during the season.
For the Australian region as a whole it was predicted that the season could be the most active season since 1983–84 and that between 20 – 22 tropical cyclones would either develop within or move into the basin compared to an average of 12 cyclones. For the Western region between 90°E and 125°E, the BoM forecast that the area would see between 11 and 12 tropical cyclones compared to the average of 7, it was also noted that the region had a 93% chance of an above average cyclone season. For the North-Western subregion between 105°E and 130°E, it was predicted that activity would be above average, with 5 tropical cyclones and a 67% chance of above average tropical cyclone activity. TCWC Perth also noted that there was a likelihood of two tropical cyclones and a significant likelihood of at least one severe tropical cyclone impacting Western Australia. It was also noted that there was an increased chance of an early season cyclone and a system impacting Western Australia before Christmas 2010. It was predicted that the Northern Territory between 125°E and 142.5°E had a 75% chance of an above average season, and that the first cyclone of the season over the Territory and the monsoon onset would be expected to be earlier than normal. The Eastern region between 142.5°E and 160°E had an 87% chance of an above average season, with 7–8 tropical cyclones predicted for the region compared to an average of 6. The BoM also issued forecasts for the Western Southern Pacific region, between 142.5°E and 165°E and the Eastern Southern Pacific region between 165°E and 120°W. It was predicted that the Western Southern Pacific would have a 79% chance of having an above average season with 7–8 tropical cyclones occurring within the region, compared to an average of 5 tropical cyclones. The Eastern Southern Pacific region was predicted to have a 33% chance of having an above average season and 5–6 tropical cyclones compared to an average of 7 tropical cyclones.
The Guy Carpenter Asia-Pacific Climate Impact Centre (GCACIC) at the City University of Hong Kong and the Tropical Storm Risk Consortium (TSR) at the University College London also issued seasonal forecasts for the region.
Seasonal summary
During the middle of October, the Madden-Julian Oscillation (MJO) moved through the eastern Indian Ocean and left an area of enhanced atmospheric convection in its wake. This subsequently combined with an equatorial Rossby wave, which contributed to the formation of Tropical Low 01U to the southwest of Sumatra, Indonesia on 28 October 2010. Over the next couple of days, the system moved westwards before it recurved south-eastwards during 30 October.
Systems
Tropical Low Anggrek
Tropical Low 01U was first noted by the BoM and BMKG during 28 October, while it was located to the southwest of Sumatra, Indonesia. Over the next day, the system moved slowly westwards, as atmospheric convection started to wrap into its consolidating low-level circulation centre, in an area of light to moderate vertical wind shear. The JTWC subsequently issued a tropical cyclone formation alert on the system during the following day, as the system turned southwards and interacted with a mid-level trough of low pressure.
On 30 October, the JTWC began issuing advisories on the system, designating it as Tropical Cyclone 02S. The next day, TCWC Jakarta reported that the low had intensified into a category 1 tropical cyclone on the Australian scale, naming it "Anggrek". Later that day, as the system moved towards the southeast, it entered the BoM's area of responsibility as it further intensified into a category 2 tropical cyclone. Anggrek passed to the east of the Cocos (Keeling) Islands early on 2 November, with the system beginning a weakening trend soon afterwards. On 4 November, TCWC Perth issued the final advisory on the system as Anggrek weakened into a tropical low. The next day, the remnants of Anggrek entered the south-west Indian Ocean as a convective-less circulation center.
Throughout the Cocos (Keeling) Islands, heavy rain and gusty winds were experienced as Cyclone Anggrek passed. Only minor damage was reported, with several trees and power lines brought down. No deaths were reported across the islands. Operationally, Anggrek peaked as a minimal tropical cyclone, however, in TCWC Perth's post-season analysis, Anggrek was downgraded to a tropical low as gale-force winds never extended more than halfway around the system center.
Tropical Cyclone Abele
During 3 December, the BoM reported that Tropical Cyclone Abele had moved into the Australian Region from the South-West Indian Ocean, as a category 2 tropical cyclone with 10-minute sustained winds of . As it entered the region the system was located well to the southwest of the Cocos (Keeling) Islands, with the JTWC reporting that the system was equivalent to a category 1 hurricane with 1-minute sustained windspeeds of . Over the next day Abele weakened further because of cooler sea surface temperatures and increasing vertical wind shear, before it was last noted by both the BoM and JTWC during 5 December.
Tropical Low 03U
On 15 December a monsoonal low developed about 500 km north-west of Exmouth, Western Australia. The system drifted slowly to the south-east. Gales and heavy rain reached areas far from the centre of the system which crossed the coast near Coral Bay on 18 December. However, shortly after landfall the system turned sharply to the south-west and reached the Indian Ocean west of Carnarvon on 19 December. It moved away from the coast and dissipated late on 20 December some 500 km west of Geraldton.
In the catchment basin of the Gascoyne River heavy precipitation fell from 16 to 19 December and triggered one of the worst floods along the Gascoyne River in history. The rain also affected other river basins in the area, such as Wooramel, Murchison, Lyndon-Minilya, and Ashburton rivers. For the period from 16 to 20 December some stations reported up to 300 mm cumulated precipitation which is equivalent to the normal annual rainfall amount. The highest 24 hours rainfall was reported at Carnarvon Airport on 17 December. During that day 207.8 mm fell which set an all-time record since recording began in 1883 with the previous record 119.4 mm set on 24 March 1923.
Preliminary estimates placed damage at A$100 million (US$100.4 million) with at least 2000 head of cattle lost in the flood.
Tropical Cyclone Tasha
Tropical Cyclone Tasha was first identified on 24 December 2010 by the Joint Typhoon Warning Centre (JTWC) as a weak area of low pressure accompanied by increasing deep convection. Situated roughly east-northeast of Cairns, Queensland, favourable environmental conditions, such as low wind shear, would allow for further development of the low. Later on 24 December, the Australian Bureau of Meteorology (BOM) classified the system as a tropical low. Shortly thereafter, the system rapidly consolidated as deep convection formed around a well-defined low-level circulation. This prompted the JTWC to issue a Tropical Cyclone Formation Alert as they anticipated the system to intensify into a tropical cyclone within the following 24 hours. At 16:00 UTC, the BOM upgraded the low to a Category 1 cyclone, assigning with the name Tasha. Within hours of the BoM declaring Tasha a tropical cyclone, the JTWC followed suit and issued their first advisory on the storm, designating it as Tropical Cyclone 04P. Situated along the northwestern edge of a subtropical ridge, Tasha tracked southwestward towards Queensland, Australia and intensified. The storm attained its peak intensity on 24 December with winds of 75 km/h (45 mph) and a barometric pressure of 993 mbar (hPa; 29.32 inHg). Hours later, the centre of Tasha made landfall between Cairns and Innisfail at this intensity. Later that day, the BOM issued their final advisory on Tasha as it weakened to a tropical low over Queensland; the JTWC followed suit shortly thereafter. The remnants of Tasha persisted in the region for several more days, bringing heavy rains to much of Queensland.
While making landfall, Tasha produced rainfall of about 100 mm in the space of an hour. Tasha contributed to floods across Queensland that forced the evacuation of thousands of people from towns and cities. Damage from associated flooding was estimated at A$1 billion.
Tropical Low 06U
On 30 December, TCWC Perth started issuing advisories on Tropical Low 06U that had developed inland over the Top End of Western Australia. On 1 January, when 06U had emerged over the Indian Ocean waters, it was forecast that it would intensify into a tropical cyclone, though shear had caused the low to struggle to develop. TCWC Perth issued its final advisory the next day as 06U weakened to a low-pressure area.
Tropical Cyclone Vince