Tag Archives: Invest 91P

Tropical Cyclone May Develop Northeast of Vanuatu

A tropical cyclone may develop over the South Pacific Ocean northeast of Vanuatu during the next several days. At 2:00 p.m. EDT on Monday the center of a low pressure system, also designated at Invest 91P, was located at latitude 13.5°S and longitude 171.7°E which put it about 375 miles (600 km) northeast of Port Vila, Vanuatu. The low pressure system was moving toward the south-southwest at 4 m.p.h (6 km/h). The maximum sustained wind speed was 20 m.p.h. (30 km/h) and there were wind gusts to 30 m.p.h. (50 km/h). The minimum surface pressure was 1010 mb.

More thunderstorms formed just to the southwest of the center of a low pressure system over the South Pacific Ocean northeast of Vanuatu on Monday. Thunderstorms also formed in bands revolving around the center of the low pressure system. The storms just southwest of the center of circulation began to generate upper level divergence that started to pump mass away from the low pressure system. The better organization exhibited by the low pressure system increased the potential that the low may develop into a tropical cyclone during the next several days.

The low pressure system will move into an environment that is favorable for the development of a tropical cyclone. The low pressure system will move over water where the Sea Surface Temperatures are near 27˚C. It will move under the western side of an upper level ridge over the South Pacific Ocean. The ridge will produce northerly winds that will blow toward the top of the low pressure system. Those winds will cause some vertical wind shear, but the shear will not be great enough to prevent intensification. The low pressure system could strengthen to a tropical cyclone during the next several days.

The low pressure system will move around the western end of a high pressure system over the South Pacific Ocean. The high pressure system will steer the low pressure system toward the south-southwest during the next several days. On its anticipated track the low pressure system could approach southern Vanuatu later this week.

Tropical Cyclone Developing East of Vanuatu

A tropical cyclone was developing east of Vanuatu on Friday night. The large low pressure system contained two smaller circulation. One circulation was already designated at Tropical Cyclone 04P by the Joint Typhoon Warning Center. At 10:00 p.m. EST on Friday the center of Tropical Cyclone 04P was located at latitude 14.9°S and longitude 175.8°E which put it about 220 miles (360 km) north-northwest of Nadi, Fiji. It was moving toward the west-southwest at 17 m.p.h. (28 km/h). The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h). The minimum surface pressure was 994 mb.

A second larger circulation designated Invest 91P was located northwest of Tropical Cyclone 04P. At 10:00 p.m. EST on Friday the center of Invest 91P was located at latitude 12.6°S and longitude 170.1°E which put it about 310 miles (500 km) east-northeast of Vanuatu. It was moving toward the east at 7 m.p.h. (11 km/h). The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h). The minimum surface pressure was 1002 mb.

Tropical Cyclone 04P and Invest 91P will rotate around each other during the next several days. The circulation around Invest 91P was larger, but the wind speeds were weaker. Upper level divergence from Invest 91P was creating vertical wind shear over Tropical Cyclone 04P. The shear was inhibiting the intensification of Tropical Cyclone 04P. The two circulations are forecast to eventually merge, but numerical models differ on which circulation will become the dominant center of circulation.

The larger environment around Tropical Cyclone 04P and Invest 91P will be favorable for intensification after the two circulations merge. The merged tropical cyclone will be over water where the Sea Surface Temperature is near 29°C. It will be in a region where the upper level winds are weak and there will be little vertical wind shear. Once Tropical Cyclone 04P and Invest 91P consolidate into a single circulation, then the tropical cyclone will intensify. It could strengthen into the equivalent of a hurricane/typhoon early next week.

Tropical Cyclone 04P and Invest 91P will rotate clockwise around each other during the weekend. The overall circulation containing the two systems is forecast to drift slowly toward the south during the next several days. On its forecast track the developing tropical cyclone will move slowly toward the south between Fiji and Vanuatu.

Tropical Low Forms Northeast of Queensland

A Tropical Low organized quickly northeast of Queensland over the Coral Sea on Thursday.  At 11:00 p.m. EDT on Thursday the center of the Tropical Low was located at latitude 16.1°S and longitude 151.4°E which put it about 370 miles (600 km) northeast of Townsville, Australia.  The Tropical Low as moving toward the south at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1005 mb.

The low level circulation of the Tropical Low organized quickly on Thursday.  Numerous bands of showers and thunderstorms formed and they began to wrap around a center of circulation.  The distribution of showers and thunderstorms was relatively symmetrical, although there are a few more storms in the eastern half of the circulation.  Storms closer to the center started to generate upper level divergence.

The Tropical Low is in an environment that is very favorable for intensification.  The low is over water where the Sea Surface Temperature is near 30°C.  The upper level winds are light and there is very little vertical wind shear.  The Tropical Low is likely to continue to organize quickly in the favorable environment and it will likely become a named tropical cyclone on Friday.  Once thunderstorms consolidate around the center of circulation, a period of rapid intensification may occur.

The Tropical Low is currently being steered to the south and that motion could continue for another 12 to 24 hours.  A strengthening subtropical ridge is forecast to turn the Tropical Low toward the west in about 24 hours.  On its anticipated track the Tropical Low could approach the coast of Queensland in about three days.