Willy developed from a weak low to the south of Java and immediately to the south of an active monsoon trough. A poorly-organised cloud cluster was evident on 2 February and during the next three days it described a clockwise loop. Increased organisation in the cloud-banding took place and cyclonic inten- sity was reached about 1800 UTC 5 February.
Further deepening occurred as Willy moved on a southwesterly track after 0000 UTC 6 February. Willy was upgraded to a severe cyclone at 1200 UTC 7 February as the estimated central pressure fell to 975 hPa. The lowest estimated central pressure was 960 hPa at around 0300 UTC 8 February. Severe cyclone status was maintained for nearly thirty-six hours as the system continued on a southwest track. GMS satellite imagery showed a clearly-defined circulation centre but an eye was visible for only a short period.
Willy decayed rapidly and lost cyclone status by 1800 UTC 9 February due to the shear created by strengthening upper-level northwesterly winds. The remnant low moved on a more southerly track and lost its identity by 0000 UTC 11 February. The strongest wind reported was 74 km/h from a ship when it was located 410 km south-southwest of the centre at 0000 UTC 9 February.