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Two Tropical Lows Form over South Pacific

Two tropical lows formed over the South Pacific Ocean on Saturday morning. The first Tropical Low formed over the Coral Sea east of the Cape York Peninsula. At 7:00 a.m. EST on Saturday the center of that Tropical Low was located at latitude 13.0°S and longitude 147.8°E which put it about 240 miles (350 km) northeast of Cooktown, Australia. The Tropical Low was nearly stationary. 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 1004 mb.

A well defined low level center of circulation formed in a small low pressure system over the Coral Sea on Saturday morning and the Australian Bureau of Meteorology designated the system as a Tropical Low. A Watch was issued for the portion of the east coast of the Cape York Peninsula from Cape Grenville to Cape Tribulation. The distribution of thunderstorms around the Tropical Low was asymmetrical. The distribution of thunderstorms around the Tropical Low was asymmetrical. The strongest thunderstorms were occurring in bands in the northwestern quadrant of the circulation. Bands in other parts of the circulation consisted primarily of showers and lower clouds. Storms near the center began to generate upper level divergence that pumped mass away from the Tropical Low.

The Tropical Low will move through an environment somewhat favorable for intensification during the next 24 hours. The Tropical Low will move over water where the Sea Surface Temperatures are near 30˚C. It will move under the northwestern part of an upper level ridge centered east of Australia. The ridge will produce easterly winds that will blow toward the top of the Tropical Low’s circulation. Those winds will cause some vertical wind shear and the shear will inhibit intensification. The Tropical Low could intensify gradually during the next 24 hours.

The Tropical Low will move north of a high pressure system centered east of Australia. The high pressure system will steer the Tropical Low toward the west during the next 24 hours. On its anticipate track the Tropical Low could approach the eastern Cape York Peninsula between Lockhart River and Cooktown in 36 hours. It could be a named tropical cyclone when it approaches the coast.

The second Tropical Low developed over the South Pacific Ocean west of Fiji. At 10:00 a.m. EST on Saturday the center of the second Tropical Low was located at latitude 18.6°S and longitude 173.3°E which put it about 320 miles (515 km) west-southwest of Nadi, Fiji. That Tropical Low was moving toward the southeast at 4 m.p.h. (6 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 1000 mb.

A distinct low level center of circulation developed in a large low pressure system over the South Pacific Ocean west of Fiji and the Fiji Meteorological Service designated the system as a tropical low. The circulation around the second Tropical Low was much larger than the one over the Coral Sea, but the distribution of thunderstorms was also asymmetrical. The strongest thunderstorms were occurring in bands north and east of the center of circulation. Bands south and west of the center consisted primarily of showers and lower clouds. Storms near the center generated upper level divergence that pumped mass away from Tropical Low.

The second Tropical Low will move through an environment favorable for intensification during the next 24 hours. The Tropical Low will move over water where the Sea Surface Temperatures are near 30˚C. It will move through an area where the upper level winds are weak and there will be little vertical wind shear. The Tropical Low is likely to intensify into a named tropical cyclone during the next 24 hours.

The second Tropical Low will be in an area where the steering currents are weak during the next 24 hours. It is likely to meander slowly over the South Pacific Ocean between Fiji and Vanuatu during the next day or so.

Tropical Low Forms Over Western Australia

An area of low pressure system has been moving across northern Australia during the past few days.  The low remains organized and the Australian Bureau of Meteorology classified the system as a Tropical Low on Wednesday because of the potential for it to develop into a tropical cyclone.  At 10:00 a.m. EST on Wednesday the center of the Tropical Low was located at latitude 15.9°S and longitude 127.0°E which put it about 80 miles (130 km) west-southwest of Wyndham, Australia.  The Tropical Low was moving toward the west at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 30 m.p.h. (50 km/h) an there were wind gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1002 mb.

There is a well defined cyclonic circulation in the lower levels of the atmosphere, but there are not many thunderstorms in the core of that circulation.  Most of the thunderstorms are developing in bands that are on the periphery of the circulation.  The strongest thunderstorms are forming in bands in the western portion of the circulation as that part of the Tropical Low begins to moves over water.  The strongest winds are also occurring in these thunderstorms that are over water.  The Tropical Low is moving underneath an upper level ridge and the ridge is causing upper level divergence which is pumping out mass.

The core of the Tropical Low is still over Western Australia and moving over land is the primary factor inhibiting intensification of the system.  The atmospheric environment is favorable for intensification.  The upper level ridge is producing light winds over the Tropical Low and there is little vertical wind shear.  The Sea Surface Temperature of the water west of Australia is near 30°C and there will be plenty of energy in the ocean to support strengthening when the core of the circulation moves west of Australia.  Some slow organization of the circulation is possible during the next 12 hours as the core of the Tropical Low moves closer to the coast of Western Australia.  Further intensification is likely during the next several days once the core of the Tropical Low moves over the warm water.  The Tropical Low could strengthen into the first named tropical cyclone of 2017 later this week.

The upper level ridge is producing light easterly winds which are slowly steering the Tropical Low toward the west.  That general motion is expected to continue for another day or so.  Eventually, the Tropical Low is forecast to move on a west-southwesterly track that would paralle, but keep it to the west of the coast of Western Australia during the next several days.