Tropical Cyclone Ilsa , the first in the Western Region for the 1999-2000 season, formed to the northeast of Cocos Islands on 11 December 1999. It was tracked for a period of almost nine days and its development was impeded by vertical windshear for a large part of its lifetime. After a long track eastwards across the Indian Ocean it eventually crossed the WA coastline along the Eighty Mile Beach during the early afternoon of 17 December. During the lifetime of Ilsa , Tropical Cyclone John formed in the Timor Sea and crossed the Pilbara coast on the morning of 15 December.
For more details see the TC Ilsa Report (pdf)
Track and intensity
All times in WST - subtract 8 hours to convert to UTC.