Tropical Cyclone Riley Strengthens to Equivalent of Hurricane/Typhoon

Tropical Cyclone Riley strengthened into the equivalent of a hurricane/typhoon on Friday.  At 4:00 p.m. EST on Friday the center of Tropical Cyclone Riley was located at latitude 17.2°S and longitude 116.9°E which put it about 415 miles (675 km) north-northeast of Learmonth, Australia.  Riley was moving toward the west at 5 m.p.h. (8 km/h).  The maximum sustained wind speed was 80 m.p.h. (130 km/h) and there were wind gusts to 100 m.p.h. (160 km/h).  The minimum surface pressure was 976 mb.

Tropical Cyclone Riley strengthened, but the distribution of thunderstorms was asymmetrical.  The strongest winds were occurring in a band the curled around the northern half of the center of circulation.  Storms in the band were generating upper level divergence which was pumping mass away from the tropical cyclone.  Other bands of showers and thunderstorms were present in the western half of the circulation, but the bands in the eastern half of Tropical Cyclone Riley consisted primarily of showers and lower clouds.  Winds to hurricane/typhoon force extended out about 35 miles (55 km) from the center of circulation and they were occurring mainly north of the center of Riley.  Winds to tropical storm force extended out about 130 miles (215 km) from the center.

Tropical Cyclone Riley was moving around the northwestern part of an upper level ridge.  The ridge was producing easterly winds which were blowing toward the top of the circulation.  Those winds appeared to converge with the upper level divergence on the east side of Riley to produce sinking motion in that part of the tropical cyclone.  The sinking motion was bringing drier air to the lower levels and it appeared to suppressing convection in that region.

Tropical Cyclone Riley may be close to its peak intensity.  Riley is currently over water where the Sea Surface Temperature is near 28°C, but it will move over cooler water during the next few days.  The upper level ridge will continue to produce easterly winds which will blow toward the top of the circulation.  Those winds could strengthen which would cause more vertical wind shear.  Riley could intensify during the next 24 hours, but it is more likely to gradually weaken during the next two or three days.

The ridge will steer Tropical Cyclone Riley toward the west-southwest during the next few days.  On its anticipated track Riley will remain north of the coast of Western Australia,  However, watches and warnings are in effect for portions of the coast in case the Tropical Cyclone Riley moves more toward the south.  A Tropical Cyclone Warning is in effect for the portion of the coast from Whim Creek to Onslow including Karratha and Dampier.  A Tropical Cyclone Watch is in effect from Onslow to Exmouth.

Elsewhere around Australia, a Tropical Low was dropping heavy rain over portions of northern Queensland.  At 1:00 p.m. EST the center of the Tropical Low was located at latitude 13.8°S and longitude 141.3°E which put it about 80 miles (125 km) north-northwest of Pormpuraaw, Australia.  It was moving toward the southeast at 6 m.p.h. (10 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 1002 mb.  Locally heavy rain could cause floods in parts of northern Queensland.