Tropical Cyclone Les

22 January - 1 February 1998


Les was the first of a group of six cyclones to develop across the Australia and South Pacific regions during an active phase of the intraseasonal oscillation in late January and early February. Les developed rapidly in the Gulf of Carpentaria and was near hurricane strength just prior to landfall on the Arnhem Land coast. Little damage was caused by the cyclone at landfall, however heavy rainfall and devastating floods in the Katherine region were produced by the remnant depression as it moved inland over the Top End of the Northern Territory. The remnants of Les continued moving west and produced gale-force winds on the Kimberley coast ofWestern Australia as the monsoon depression intensified temporarily near the coast before moving further inland.

A deep westerly monsoon surge interacted with a low embedded in the monsoon trough in the Gulf of Carpentaria on 20 January. The surge eased after several days. By this stage the low-level centre had been pushed over Cape York Peninsula. The low started developing a more organised structure during 22 January, with rainbands over the land and sea either side of the peninsula around the centre. Upper-level return equatorial easterly flow was well developed with a 25 m/s jet over Papua New Guinea and Indonesia. At this time a strengthening high pressure ridge in the low to middle levels over Queensland initially pushed the low north along the Peninsula, then westward, returning it to the Gulf of Carpentaria. Deep convection persisted near the low's centre as it moved in the Gulf of Carpentaria and Les formed early on 24 January, about 12 hours after moving over the sea. The cyclone intensified rapidly with favourable upper outflow, attaining near hurricane strength 24 hours after initial development. Les showed signs of eye formation before its intensification was temporarily retarded as the core crossed the south coast of Groote Eylandt. Some re-intensification occurred in the eighty km of sea between Groote Eylandt and the mainland. A peak wind gust of 47 m/s was recorded by a bulk ore carrier in Les 's path in this area.At this time the gale radius extended to 110 km, storm force winds to 35 km and the radius of calm winds to about 7 km. Les passed over the town of Numbulwar on the mainland coast early on 25 January.

There were several roofs blown off old houses, trees blown down and power outages at Numbulwar and the communities on Groote Eylandt. Local flooding was reported as well as a one metre rise in sea level above high tide at Alyangula, the Groote Eylandt port.

The westward steering continued to dominate over the next five days as the post-cyclone low crossed the Top End of the Northern Territory, Joseph Bonaparte Gulf then the north Kimberley coast. As ex- Les crossed the Top End of the Northern Territory during the period 25 to 29 January record rainfall fell in the catchment of the Katherine River. In the 72 hours to 2330 UTC 27 January 400 to 550 mm of rainfall was recorded, causing the most significant flood on record in the Katherine and Daly rivers. Thousands of residents in the towns of Katherine, and the communities of Mataranka, Palumpa, Peppimenarti, Daly River and Beswick were evacuated. Three people drowned. The flood covered an area of about a thousand square km, affected 1100 dwellings and flooded every business and overnment office in the central business district of Katherine. About 640 business owners, primary producers, and contractors were affected. Road traffic was severely disrupted with highways washed out in many places across the region. Darwin was cut off from the remainder of the country by road and many travellers and goods were stranded for at least five days. Telecommunications were also severely disrupted with one of the two fibre optic cables connecting the Top End with the remainder of Australia being cut. Repairs to flood damaged buildings and infrastructure in Katherine were estimated to have cost more than A$100m.

As the ex- Les low continued westward it crossed into the Joseph Bonaparte Gulf on 29 January before once again moving over land on the north Kimberley coast. Gales were observed along the Kimberley with the low having the structure of a well-developed monsoon low with gales at a large distance from the centre. Flooding and damage to trees and power lines occurred in the Kimberley communities of Kalumburu and Oombulgurri. The low followed the west Kimberley coast, causing some minor tree damage at Broome and around 200 mm of rain in two days before moving inland and weakening over the Pilbara region of West Australia.

Track and intensity

All times in UTC - add 9.5 hours to convert to CST.

Best Track of Tropical Cyclone Les