Tropical Cyclone Iris Weakens East of Queensland

Tropical Cyclone Iris weakened over the Coral Sea east of Queensland on Wednesday.  At 11:00 p.m. EDT on Wednesday the center of Tropical Cyclone Iris was located at latitude 19.6°S and longitude 152.3°E which put it about 230 miles (370 km) east-northeast of Mackay, Australia.  Iris was moving toward the east-southeast at 4 m.p.h. (6 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 990 mb.

An upper level ridge east of Australia was producing strong northwesterly winds which were blowing toward the top of Tropical Cyclone Iris.  Those winds were causing strong vertical wind shear which weakened Iris on Wednesday.  The stronger thunderstorms were occurring in bands southeast of the center of circulation.  The bands in other parts of the circulation consisted primarily of showers and low clouds.  The wind shear was not quite strong enough to blow the top off of the circulation, but the shear was preventing upper level divergence on the northern side of Tropical Cyclone Iris.

Tropical Cyclone Iris will move over water where the Sea Surface Temperature is near 28°C.  So, there is enough energy in the upper ocean to support a tropical cyclone.  However, the upper level ridge will continue to cause strong vertical wind shear and Tropical Cyclone Iris is likely to slowly weaken during the next several days.

Tropical Cyclone Iris is moving slowly toward the east-southeast.  If the vertical wind shear blows the top half of the circulation away to the southeast, then Iris would be steered by the winds in the lower atmosphere.  A high pressure system in the lower atmosphere over Australia would begin to steer Tropical Cyclone Iris back toward the northwest.  On its anticipated track the center of Tropical Cyclone Iris is expected to remain east of Queensland.  Rainbands on the western periphery have occasionally brought rain to the coast of Queensland, but most of the rain is falling over the ocean.