Tropical Cyclone Seth sped toward the south over the Coral Sea east of Australia on Saturday night. At 7:00 p.m. EST on Saturday the center of Tropical Cyclone Seth was located at latitude 25.8°S and longitude 159.0°E which put it about 385 miles (620 km) east-northeast of Brisbane, Australia. Seth was moving toward the south at 25 m.p.h. (41 km/h). The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h). The minimum surface pressure was 987 mb.
An upper level trough over eastern Australia and an upper level ridge east of the Coral Sea were combining to steer Tropical Cyclone Seth quickly toward the south on Saturday night. The structure of Seth’s circulation was beginning to resemble a subtropical cyclone. The strongest thunderstorms were occurring in bands south of the center of circulation. Bands in the northern half of Tropical Cyclone Seth consisted primarily of showers and lower clouds. The upper level trough and upper level ridge were producing strong northerly winds that were blowing toward the top of Seth’s circulation. Those winds were causing strong vertical wind shear. Drier air was wrapping around the northern side of Tropical Cyclone Seth. The strong vertical wind shear and drier air were causing the asymmetrical distribution of thunderstorms. The distribution of winds around Seth was also asymmetrical. Winds to tropical storm force extended out 205 miles (335 km) in the southern half of Tropical Cyclone Seth. Winds to tropical storm force extended out 90 miles (150 km) in the northern half of Seth’s circulation.
Tropical Cyclone Seth will move through an environment unfavorable for intensification during the next 24 hours. Seth will move over water where the Sea Surface Temperatures are near 26˚C. However, the upper level trough and upper level ridge will continue to cause strong vertical wind shear. Drier air in the northern half of Seth’s circulation will inhibit the formation of thunderstorms. Tropical Cyclone Seth could make a transition to a subtropical cyclone during the next 24 hours. Seth could maintain its intensity during the transition, but it is likely to weaken during the next few days.
The upper level trough will steer Tropical Cyclone Seth quickly toward the south during the next 12 hours. The upper trough could make a transition to a cutoff low during the next day or so. The center of Seth could move under the cutoff low, which would cause Seth to move more slowly. The cutoff low and Tropical Cyclone Seth could drift west toward Australia during the next several days. On its anticipated track Tropical Cyclone Seth could move slowly toward Australia as a subtropical cyclone.