Rare Late Season Tropical Cyclone Forms over South Indian Ocean

A rare late season tropical cyclone formed over the South Indian Ocean on Thursday. At 5:00 p.m. EDT on Thursday the center of Tropical Cyclone 01S was located at latitude 10.7°S and longitude 95.0°E which put it about 170 miles (275 km) west-northwest of Cocos Island. Tropical Cyclone 01S was moving toward the southeast at 7 m.p.h. (11 km/h). The maximum sustained wind speed was 40 m.p.h. (65 km/h) and and there were wind gusts to 50 m.p.h. (80 km/h). The minimum surface pressure was 1002 mb.

The circulation around a low pressure system over the South Indian Ocean west-northwest of Cocos Island strengthened on Thursday and the Joint Typhoon Warning Center and the Australian Bureau of Meteorology both designated the system as a tropical cyclone. It is unusual for a tropical cyclone to form this late in the season in the southern hemisphere. It is the equivalent of a tropical cyclone forming in late January in the northern hemisphere.

The distribution of thunderstorms around Tropical Cyclone 01S was asymmetrical. The strongest thunderstorms were occurring in bands in the southern half of the tropical cyclone. Bands in the northern half of Tropical Cyclone 01S consisted primarily of showers and lower clouds. Tropical Cyclone 01S was under the southwestern part of an upper level ridge centered northwest of Australia. The upper level ridge was producing northerly winds that were blowing toward the top of the tropical cyclone’s circulation. Those winds were causing moderate vertical wind shear. The wind shear was causing the asymmetrical distribution of thunderstorms. Winds to tropical storm force extended out 170 miles (275 km) in the southeastern quadrant of Tropical Cyclone 01S. Winds in the other parts of the tropical cyclone were blowing at less than tropical storm force.

Tropical Cyclone 01S will move through an environment somewhat favorable for intensification during the next 24 hours. The tropical cyclone will move over water where the Sea Surface Temperatures are near 28˚C. However, the upper level ridge northwest of Australia will continue to cause moderate vertical wind shear. Tropical Cyclone 01S could strengthen a little more during the next 24 hours, but the moderate vertical wind shear will limit intensification.

Tropical Cyclone 01S will move north of a high pressure system over the South Indian Ocean during the next several days. The high pressure system will steer the tropical cyclone toward the west. On its anticipated track Tropical Cyclone 01S will begin to move farther away from Cocos Island.