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Weaker Tropical Cyclone Ann Nears Northern Queensland

A weaker Tropical Cyclone Ann neared northern Queensland on Monday.  At 11:00 p.m. EDT on Monday the center of Tropical Cyclone Ann was located at latitude 14.4°S and longitude 148.4°E which put it about 230 miles (370 km) east-northeast of Cooktown, Australia.  Ann was moving toward the west-northwest at 14 m.p.h. (22km/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 996 mb.  The Australian Bureau of Meteorology issued a Tropical Cyclone Warning that extended from Lockhart River to Cooktown including Coen and Lizard Island.

The circulation around Tropical Cyclone Ann weakened on Monday because of a drier, more stable environment and more vertical wind shear.  Low level convergence pulled drier, more stable air closer to the center of Tropical Cyclone Ann.  The drier, more stable air caused many of the stronger thunderstorms to weaken.  Despite the drier, more stable environment stronger thunderstorms redeveloped south of the center of circulation late on Monday.  Tropical Cyclone Ann was moving near the northwestern portion of an upper level ridge.  The ridge produced easterly winds which caused moderate vertical wind shear.  The wind shear also contributed to the weakening of storms in the northern half of the circulation.

Tropical Cyclone Ann continued to have a distinct low level center of circulation despite the less favorable environment.  However, the wind field exhibited a more asymmetric structure.  The strongest winds were occurring in an area of thunderstorms south of the center of circulation.  Winds to tropical storm force extended out about 100 miles (160 km) from the center in the southern half of the circulation.  Winds to tropical storm force only extended out about 50 miles (80 km) from the center in the northern half of the circulation.

Tropical Cyclone Ann will continue to move through a less favorable environment during the next 24 hours.  Ann will move over water in the Coral Sea where the Sea Surface Temperature is near 27.5°C.  It will continue to move through a region where there is drier, more stable air and the upper level ridge will continue to cause moderate vertical wind shear.  The drier, more stable air and moderate vertical wind shear will prevent significant intensification.  Tropical Cyclone Ann could maintain its intensity during the next 12 hours, but it may weaken when it approaches the coast of the Cape York Peninsula.

Tropical Cyclone Ann will move north of a ridge which will steer Ann toward the west-northwest.  On its anticipated track Tropical Cyclone Ann will make landfall on the Cape York Peninsula in northern Queensland in about 24 hours.  Ann will bring some gusty winds, but the greatest risk will be locally heavy rain.

Tropical Cyclone Ann Strengthens Over Coral Sea

Tropical Cyclone Ann strengthened over the Coral Sea on Sunday.  At 11:00 p.m. EDT on Sunday the center of Tropical Cyclone Ann was located at latitude 15.4°S and longitude 153.6°E which put it about 565 miles (910 km) east of Cairns, Australia.  Ann was moving toward the west-northwest at 15 m.p.h. (24 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h).  The minimum surface pressure was 987 mb.

The circulation around Tropical Cyclone Ann exhibited greater organization on Sunday.  There were indications on satellite images that a cloud filled eye might be trying to form at the center of circulation.  A broken ring of thunderstorms surrounded the eye and the strongest winds were occurring in that ring of storms.  Several bands of showers and thunderstorms were revolving around the core of Tropical Cyclone Ann.  Storms near the core were generating upper level divergence which was pumping mass away from the tropical cyclone.  Winds to tropical storm force extended out about 100 miles (160 km) from the center of circulation.

Tropical Cyclone Ann will be moving through an environment that contains factors favorable for intensification and a factor that will inhibit potential intensification.  Ann will move over water where the Sea Surface Temperature is near 28°C.  So, there will be sufficient energy in the upper ocean to support intensification.  Tropical Cyclone Ann will move north of an upper level ridge.  The ridge will produce easterly winds which will blow toward the top of the circulation.  Those winds will cause some vertical wind shear, but the shear will not be strong enough to prevent intensification.  Tropical Cyclone Ann is surrounded by drier more stable air and the drier air is the factor that will inhibit intensification.  So far, the circulation around Ann has kept the drier air outside the tropical cyclone.  If the drier air remains outside the circulation, then Tropical Cyclone Ann would have a chance to strengthen.  However, if the drier air gets pulled into the circulation, then Ann will weaken.  The higher probability is that Tropical Cyclone Ann could maintain its intensity or weaken slowly during the next day or two depending on what happens to the drier air.

Tropical Cyclone Ann will move north of an area of high pressure, which will steer the tropical cyclone toward the west-northwest.  On its anticipated track Ann will approach the Cape York Peninsula north of Coen in less than 48 hours.  Tropical Cyclone Ann could bring gusty winds and locally heavy rain to northern Queensland.