Miriam and Norman Become Hurricanes

Both former Tropical Storm Miriam and Tropical Storm Norman strengthened into hurricanes over the Eastern North Pacific on Wednesday afternoon.  At 5:00 p.m. EDT on Wednesday the center of Hurricane Miriam was located at latitude 14.0°N and longitude 139.7°W which put it about 1090 miles east of Hilo, Hawaii.  Miriam was moving toward the west at 9 m.p.h.  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 992 mb.

At 5:00 p.m. EDT on Wednesday the center of Hurricane Norman was located at latitude 17.6°N and longitude 116.9°W which put it about 545 miles (875 km) southwest of the southern tip of Baja California.  Norman was moving toward the west at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts t0 90 m.p.h. (145 km/h).  The minimum surface pressure was 987 mb.

An inner rainband wrapped much of the way around the center of circulation and an eye developed at the center  of Hurricane Miriam on Wednesday.  Storms near the core of Miriam generated strong upper level divergence which pumped mass away from the hurricane.  Several bands of showers and thunderstorms were revolving around the core of the circulation.  The strongest rainbands were south and east of the center of Hurricane Miriam.  Rainbands on the northwest side of the circulation contained more showers and low clouds.

An inner rainband also wrapped most of the way around the center of Hurricane Norman on Wednesday and an eye appeared to be forming at the center of circulation.  Several bands of showers and thunderstorms were revolving around the core of Norman.  The distribution of thunderstorms in Norman was more symmetrical.  Storms around the core of Hurricane Norman were generating well developed upper level divergence.

Both Hurricane Miriam and Hurricane Norman were moving south of a subtropical ridge over the Eastern North Pacific Ocean.  Miriam could reach the end of the ridge in the next day or two and turn toward the north.  The ridge is forecast to steer Hurricane Norman westward during the next two or three days.

Hurricane Miriam will approach an upper level trough east of Hawaii.  The trough will produce southwesterly winds which will increase vertical wind shear.  The shear is forecast to cause Miriam to weaken.  Hurricane Norman will move over water where the Sea Surface Temperature is near 28°C.  Norman will move through a region where the upper level winds are weak and there will be little vertical wind shear.  Norman is forecast to intensify into a major hurricane.