 The monsoon trough spawned a tropical low about 550 km ( 340 mi ) east of the Cocos Islands on February 24 . Located in the Australian basin , it quickly intensified to tropical storm status and was named " Harriet " by the BoM , and Tropical Cyclone 20S by the JTWC . After passing just south of North Keeling Island , Harriet turned more to the southwest , and strengthened into a Category 5 on the Australian tropical cyclone intensity scale on March 1 . By that time , the MFR had begun issuing advisories , and later that day renamed Harriet as Heather after the cyclone crossed into the south @-@ west Indian Ocean . When Heather reached the basin , the JTWC was estimating peak 1 ‑ minute winds of 220 km / h ( 140 mph ) , and shortly thereafter the MFR estimated peak 10 ‑ minute winds of 165 km / h ( 105 mph ) . 
