Hurricane Aletta has already begun to weaken after becoming the first major hurricane of the 2018 Eastern Pacific hurricane season, while another area off the Mexican coast is expected to become the second named storm this weekend.
Aletta is centered just under 500 miles south of Mexico’s Baja Peninsula.
In just 24 hours, Aletta went from a tropical storm to a Category 4 hurricane, doubling its maximum sustained winds (70 mph to 140 mph) by the 9 a.m. MDT Friday National Hurricane Center advisory.
Infrared satellite imagery shows that Aletta’s cloud pattern has become less symmetric and an eye is no longer visible.
The combination of increased wind shear and quickly decreasing ocean heat content will cause Aletta to continue to quickly weaken this weekend as it moves into the open Pacific.
Fortunately, a dome of high pressure aloft over northern Mexico is steering Aletta away from the Mexican coast on a general west-northwest track this weekend.
To the east of Aletta, another area of low pressure, a tropical wave, is given high odds by the NHC to develop into a tropical depression or tropical storm this weekend south of the Mexican Riviera.
The National Hurricane Center noted in its 5 a.m. PDT outlook that this system, located about 400 miles south of Acapulco, Mexico, is becoming better organized and if current trends continue, advisories could be initiated later Saturday.
If it eventually becomes a tropical storm, it would earn the name Bud.
It’s too soon to determine whether this second system will eventually pose a direct threat to parts of the Mexican Pacific coast next week.
For now, interests along the Mexican coast from Acapulco to Zihuatanejo, Manzanillo, Puerto Vallarta and Los Cabos should monitor the progress of this second system into next week.
At least some peripheral impacts are possible near the coast from each system, even if the centers of both systems remain offshore.
Some outer rainbands will likely push ashore, at times, through next week, possibly triggering local flash flooding if they persist in any area for a few hours at a time.
High surf will be generated, propagating first to the southern Mexican coast, then pushing northward toward the Baja Peninsula, including Los Cabos. Breaking waves and rip currents will be a threat along those beaches into at next week.
The average date when the first named storm forms in the Eastern Pacific Basin is June 10, according to NHC data from 1971 to 2009. An average Eastern Pacific hurricane season sees the first hurricane form by June 26.
It’s not unusual for the Eastern Pacific season’s first storm to be a Category 4 hurricane. It’s happened seven other times since 1970, according to NOAA’s historical hurricanes database.
The 2015 season began with Category 4 Hurricane Andres, followed by Category 4 Hurricane Blanca, the record earliest-in-season second Eastern Pacific hurricane and major hurricane, which later became the record earliest Baja California landfall, as a tropical storm.
However, only one of these “A” hurricanes has reached Category 5 intensity, Hurricane Ava in June 1973, according to NOAA.