Hurricane Aletta Rapidly Intensifies to Category 4

Hurricane Aletta rapidly intensified Friday morning to Category 4 on the Saffir-Simpson Scale.  At 11:00 a.m. EDT on Friday the center of Hurricane Aletta was located at latitude 15.8°N and longitude 111.2°W which put it about 505 miles (815 km) west-southwest of Manzanillo, Mexico.  Aletta was moving toward the west at 5 m.p.h. (8 km/h).  The maximum sustained wind speed was 140 m.p.h. (220 km/h) and there were wind gusts to 165 m.p.h. (265 km/h).  The minimum surface pressure was 943 mb.

An environment with warm Sea Surface Temperatures and little vertical wind shear allowed Hurricane Aletta to intensify rapidly during Thursday night and Friday morning.  A small circular eye was evident at the center of circulation.  A tight ring of strong thunderstorms completely surrounded the eye and the strongest winds were occurring in that ring of storms.  Several bands of strong storms were revolving around the eastern and northern sides of the core of Hurricane Aletta.  Storms around the core were generating very strong upper level divergence which was pumping away large quantities of mass from the hurricane.  The removal of mass allowed the pressure to decrease rapidly and a stronger pressure gradient force generated much stronger winds.

Hurricane Aletta has a relatively small circulation.  Winds to hurricane force extended out about 30 miles (50 km) from the center of circulation.  Winds to tropical storm force extended out about 100 miles (160 km) from the center.  The Hurricane Intensity Index (HII) was 28.3.  The Hurricane Size Index (HSI) was 10.8 and the Hurricane Wind Intensity Size Index (HWISI) was 39.1.  Hurricane Aletta is very similar in intensity and size to Hurricane Charley in 2004 when Charley hit southwest Florida.

Hurricane Aletta will remain in a favorable environment of warm water and little vertical wind shear for another 12 to 24 hours.  So, it could strengthen more in the short term.  Aletta will start to move over cooler water during the next day or so.  There will be less energy in the upper ocean to support the intense hurricane.  In addition, a upper level trough to the northwest of Aletta will produce southwesterly winds which will blow toward the top of the circulation.  Increased vertical wind shear will speed up the rate of weakening.  Since the circulation of Hurricane Aletta is relatively small, it could weaken fairly quickly.

Hurricane Aletta is moving around the southwestern part of a ridge over Mexico.  The ridge has been steering Aletta toward the west.  A turn more toward the northwest is expected when Hurricane Aletta nears the western end of the ridge.  On its anticipated track Hurricane Aletta is forecast to move farther away from the west coast of Mexico.