Tropical Cyclone Frances Develops North of Western Australia

An area of low pressure northwest of Western Australia developed into Tropical Cyclone Frances on Thursday.  At 10:00 a.m. EDT on Thursday the center of Tropical Cyclone Frances was located at latitude 11.0°S and longitude 128.3°E which put it about 255 miles (410 km) north-northeast of Kalumburu, Australia.  Frances was moving toward the west-southwest at 12 m.p.h. (19 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. (110 km/h).  The minimum surface pressure was 997 mb.

The organization of Tropical Cyclone Frances improved significantly during the past 24 hours.  A well organized center of circulation developed at the surface.  A primary rainband wrapped about two-thirds of the way around the southern and western sides of the center.  Additional bands of showers and thunderstorms formed in the outer portions of the circulation.  Thunderstorms near the core of the circulation generated upper level divergence which was pumping mass away to the south of the tropical cyclone.  Frances is a fairly small tropical cyclone and winds to tropical storm force only extend out about 100 miles (160 km) from the center.

Tropical Cyclone Frances will move through an environment that will be favorable for intensification during the next 24 to 36 hours.  Frances will move over water where the Sea Surface Temperature is near 30°C while is moves across the Timor Sea.  An upper level ridge east of Tropical Cyclone Frances is producing northeasterly winds which are blowing toward the top of the circulation.  Vertical wind shear may be the reason that the primary rainband wrapped around the southern and western sides of the center.  However, the vertical shear does not appear to be strong enough to significantly affect the upper level divergence.  Frances is likely to intensify during the next day or so.  Eventually, Tropical Cyclone Frances will move into an area where there are strong upper level northwesterly winds.  A significant increase in vertical wind shear should weaken Frances when that occurs.

A subtropical ridge to the east of Frances is steering the tropical cyclone toward the west-southwest.  A general motion toward the west-southwest is expected to continue during the next few days.  On its anticipated track the center of Tropical Cyclone Frances is forecast to stay north of the coast of Western Australia.  However, any southward deviation of the track could bring stronger winds closer to the coast.