Monthly Archives: April 2023

Tropical Low Forms over Timor Sea

A Tropical Low formed over the Timor Sea northwest of Darwin Australia on Saturday. At 8:00 a.m. EDT on Saturday the center of the Tropical Low was located at latitude 10.3°S and longitude 129.0°E which put it about 105 miles (165 km) northwest of Darwin, Australia. The Tropical Low was moving toward the southwest at 6 m.p.h. (9 km/h). The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h). The minimum surface pressure was 996 mb.

A Tropical Cyclone Watch was in effect for the portion of the coast of Western Australia from Kalumburu to Cockatoo Island.

A low pressure system over the Timor Sea northwest of Darwin, Australia strengthened on Saturday morning and the Australian Bureau of Meteorology designated the system as a Tropical Low. The distribution of thunderstorms around the Tropical Low was asymmetrical. Most thunderstorms were occurring in bands in the western half of the circulation. Bands in the eastern side of the Tropical Low consisted primarily of showers and lower clouds. The Tropical Low was moving under the northern part of an upper level ridge over northern Australia. The ridge was producing easterly winds that were blowing toward the top of the Tropical Low. Those winds were causing moderate vertical wind shear and the wind shear was causing the asymmetrical distribution of thunderstorms. Storms near the center of circulation generated upper level divergence that pumped mass away to the west of the tropical low.

The Tropical Low will move through an environment that will be somewhat favorable for intensification during the next 36 hours. The Tropical Low will move over water where the Sea Surface Temperatures are near 31˚C. However, the upper level ridge over northern Australia will continue to cause moderate vertical wind shear. The Tropical Low is likely to intensify gradually during the next 36 hours. It could become a named tropical cyclone during that time.

The Tropical Low will move around the northwest part of a high pressure system over western Australia. The high pressure system will steer the Tropical Low toward the southwest during the next 36 hours. On its anticipated track, the Tropical Low will move parallel to the coast of Western Australia during the weekend.

NHC To Extend Tropical Weather Outlook to Seven Days in 2023

The National Hurricane Center (NHC) stated that it will extend the length of the period covered by the Tropical Weather Outlook (TWO) from five to seven days in 2023. Both the textual and graphical outlooks will be extended to seven days. NHC also indicated that it will begin to include invest numbers in the Tropical Weather Outlook, when it is appropriate.

NHC is going to remove information on land based tropical cyclone watches and warnings from the Tropical Cyclone Forecast/Advisories. NHC will continue to provide information on land based tropical cyclone watches and warnings in the Tropical Cyclone Public Advisories.

NHC will make the Peak Storm Surge Forecast graphic operational in 2023. The Peak Storm Surge Forecast graphic provided in previous years was considered experimental.

The Peak Storm Surge Flooding Map issued by NHC will now also be issued for Puerto Rico and the U.S. Virgin Islands.

Tropical Cyclone Herman Weakens Southeast of Cocos Islands

Tropical Cyclone Herman weakened over the South Indian Ocean southeast of the Cocos Islands on Saturday. At 5:00 p.m. EDT on Saturday the center of Tropical Cyclone Herman was located at latitude 19.9°S and longitude 106.7°E which put it about 865 miles (1395 km) southeast of the Cocos Islands. Herman was moving toward the south-southwest at 5 m.p.h. (8 km/h). The maximum sustained wind speed was 80 m.p.h. (130 km/h) and there were wind gusts to 100 m.p.h. (160 km/h). The minimum surface pressure was 978 mb.

Tropical Cyclone Herman weakened on Saturday. An upper level trough over the South Indian Ocean produced northwesterly winds that blew toward the top of Herman’s circulation. Those winds caused moderate vertical wind shear and the wind shear caused Tropical Cyclone Herman to weaken. An eye was no longer evident on satellite images of Herman. The inner end of a rainband still wrapped around the southern and western sides of the center of Herman’s circulation. The circulation around Tropical Cyclone Herman was small. Winds to hurricane/typhoon force extended out 20 miles (30 km) from the center of Herman. Winds to tropical storm force extended out 60 miles (95 km) from the center of circulation.

Tropical Cyclone Herman will move through an environment that will be unfavorable for intensification during the next 36 hours. Herman will move over water where the Sea Surface Temperatures are near 26˚C. However, the upper level trough over the South Indian Ocean will continue to produce northwesterly winds that will blow toward the top of Herman’s circulation. Those winds will continue to cause moderate vertical wind shear and the wind shear will cause Tropical Cyclone Herman to weaken. Since Herman’s circulation is small, the tropical cyclone could weaken rapidly at times.

Tropical Cyclone Herman will move north of high pressure system over the South Indian Ocean. The high pressure system will steer Herman toward the west during the next 36 hours. On its anticipated track, Tropical Cyclone Herman will remain far to the south of the Cocos Islands.