Tag Archives: Australia

Tropical Cyclone Nathan Forms Over the Coral Sea

Another tropical cyclone formed in an elongated trough of low pressure over the southwestern Pacific Ocean.  At 10:00 p.m. EDT on Tuesday the center of Tropical Storm Nathan was located at latitude 13.8°S and longitude 146.8°E which put it about 150 miles northeast of Cooktown, Australia and about 250 miles south of Port Moresby, Papua New Guinea.  It was moving toward the west-southwest at 9 m.p.h.  The maximum sustained wind speed was 60 m.p.h. and there were wind gusts to 80 m.p.h.  The minimum surface pressure was 989 mb.

Nathan is over warm Sea Surface Temperatures, but it is being partly influenced by some of the upper level outflow from large Tropical Cyclone Pam which is located farther east.  The wind shear is reducing the rate of intensification, but the environment is favorable enough that continued intensification is likely during the next day or two.

The track forecast for Nathan has a high degree of uncertainty.  It is currently being steered to the west-southwest by a subtropical ridge that is north of the circulation center.  That ridge is predicted to weaken and westerly winds are expected to turn the tropical cyclone back toward the east.  However, the timing of that turn is important.  The center of Nathan could come very close to the coast of Queensland.  If the turn does not occur, Nathan could bring high winds and heavy rain to portions of northern Queensland.

 

Tropical Cyclone Ola Intensifying Northwest of New Caledonia

Tropical Cyclone Ola intensified rapidly on Saturday as it moved over the Coral Sea northwest of New Caledonia.  At 8:00 p.m. EST on Saturday the center of Ola was located at latitude 19.9°S and longitude 162.9°E which put it about 260 miles northwest of Noumea, New Caledonia.  Ola was moving toward the south-southeast at 8 m.p.h.  The maximum sustained wind speed was 80 m.p.h. and there were gusts to 95 m.p.h.  The minimum surface pressure was 970 mb.

Ola is moving over warm Sea Surface Temperatures (SSTs) and the environmental winds are generating upper level divergence to the southeast of the circulation.  The divergence pumped out mass and surface pressure decreased rapidly.  As a result, Ola intensified into the equivalent of a hurricane on Saturday.  Ola will remain over warm SSTs, but it will move into an area of stronger upper level winds when it moves farther southward.  It could intensify more during the next 24 hours, but it is likely to begin to weaken in 36 to 48 hours because of increasing vertical wind shear.

Counterclockwise flow around the western end of a subtropical ridge is steering Ola in a general southward direction.  That motion is expected to continue for another 24 hours.  A ridge of high pressure is expected to build south of Ola in a day or so.  The ridge could block Ola from moving any farther toward the south and turn it toward the southwest.  On the expected track, Ola would stay west of New Caledonia.  It is expected to weaken before it reaches Australia.