Tropical Cyclone Herman rapidly intensified to the equivalent of a hurricane/typhoon over the South Indian Ocean northwest of Australia on Thursday. At 5:00 p.m. EDT on Thursday the center of Tropical Cyclone Herman was located at latitude 16.5°S and longitude 106.0°E which put it about 665 miles (1070 km) east-southeast of Cocos Islands. Herman was moving toward the south-southeast at 9 m.p.h. (15 km/h). The maximum sustained wind speed was 110 m.p.h. (175 km/h) and there were wind gusts to 130 m.p.h. (210 km/h). The minimum surface pressure was 959 mb.
Tropical Cyclone Herman rapidly intensified to nearly the equivalent of a major hurricane over the South Indian Ocean on Thursday. A small circular eye was present at the center of Herman’s circulation. A ring of strong thunderstorms surrounded the eye and the strongest winds were occurring in that ring of storms. Bands of showers and thunderstorms were revolving around the center of Tropical Cyclone Herman. Storms near the center generated upper level divergence that pumped mass away to the southeast of the tropical cyclone.
The circulation around Tropical Cyclone Herman was small. Winds to hurricane/typhoon force extended out 25 miles (40 km) from the center of Herman. Winds to tropical storm force extended out 80 miles (130 km) from the center of circulation. The Hurricane Intensity Index (HII) for Tropical Cyclone Herman was 19.2. The Hurricane Size Index (HSI) was 9.4 and the Hurricane Wind Intensity Size Index (HWISI) was 28.6. Tropical Cyclone Herman was similar in size and intensity to Hurricane Zeta when Zeta made landfall in Louisiana in 2020.
Tropical Cyclone Herman will move through an environment that will become unfavorable for intensification during the next 24 hours. Herman will move over water where the Sea Surface Temperatures are near 28˚C. However, an upper level trough will approach Tropical Cyclone Herman from the west. The upper level trough will produce northwesterly winds that will get stronger during the next 24 hours. Those stronger winds will blow toward the top of Herman’s circulation and the vertical wind shear will increase. More vertical wind shear will cause Tropical Cyclone Herman to weaken.
The upper level trough will steer Tropical Cyclone Herman toward the south-southeast during the next 24 hours. On its anticipated track Tropical Cyclone Herman will move farther away from Cocos Islands. When the stronger vertical wind shear causes Herman to weaken, it will be steered by the winds closer to the surface. Those winds will steer Tropical Cyclone Herman toward the west during the weekend.