Tropical Storm Aletta formed over the Eastern North Pacific Ocean west of Mexico on Thursday afternoon.  This is the latest date for the formation of the first tropical storm over the Eastern North Pacific basin during the satellite era.  At 5:00 p.m. EDT on Thursday the center of Tropical Storm Aletta was located at latitude 17.9°N and longitude 107.0°W which put the center about 190 miles (310 km) west-southwest of Manzanillo, Mexico.  Aletta was moving toward the northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1005 mb.

A low pressure system over the Eastern North Pacific Ocean west of Mexico strengthened on Thursday afternoon and the U.S. National Hurricane Center designated the system as Tropical Storm Aletta.  More thunderstorms formed near the center of Aletta’s circulation.  Thunderstorms were also occurring in a band in the western part of Tropical Storm Aletta.  Bands in the other parts of Aletta’s circulation consisted primarily of showers and lower clouds.  Storm near the center of Aletta began to generate upper level divergence that pumped mass away from the tropical storm.

The circulation around Tropical Storm Aletta was very small.  Winds to tropical storm force extended out 45 miles (75 km) in the northern half of Aletta’s circulation.  The winds in the souther half of Tropical Storm Aletta were blowing at less than tropical storm force.

Tropical Storm Aletta will move into an environment that will become unfavorable for intensification during the next 24 hours.  Aletta will move over water where the Sea Surface Temperatures are near 26°C.  It will move under the southern part of an upper level ridge over the Southwest U.S.  The upper level ridge will produce easterly wind that will blow toward the top of Aletta’s circulation.  Those winds will cause moderate vertical wind shear.  Tropical Storm Aletta could intensify a little during Thursday night, but cooler water and moderate wind shear are likely to end the intensification by Friday morning.  Aletta is likely to weaken to a tropical depression on Friday.

Tropical Storm Aletta will move around the southern side of a high pressure system over the Eastern North Pacific Ocean.  The high pressure system will steer Aletta toward the west during the next 24 hours.  On its anticipated track, Tropical Storm Aletta will move farther away from the coast of Mexico.