Unexpectedly, Hurricane Aletta over the eastern Pacific underwent a remarkable period of rapid intensification overnight, and is now a Category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. Although some slight additional intensification cannot be ruled out, Aletta is likely close to its peak intensity and weakening should commence tonight or early tomorrow. Aletta remains no threat to land. To the east of Aletta, Invest 92E has been designated, and is expected to develop into a tropical depression this weekend off the Pacific coast of Mexico. There are still indications on the models that the Caribbean and Gulf of Mexico may warrant monitoring by late next week, but this remains uncertain.

As of 9:00 a.m. MDT (11:00 a.m. EDT), Hurricane Aletta was centered near 15.8°N 111.2°W, and was moving westward at about 5 mph. Maximum sustained winds were 120 knots (140 mph), with an estimated minimum pressure of 943 mb. Aletta now has a lower minimum pressure than any eastern Pacific tropical cyclones of 2017. The average first major hurricane in the eastern Pacific basin does not form until July 19, so Aletta is well ahead of schedule. The rapid intensification of Aletta was poorly forecast by the intensity guidance, although the GFS model was fairly consistent with rapid deepening. Aletta is likely near its peak intensity. A combination of eyewall replacement cycles, rapidly cooling sea surface temperatures and an increasingly dry environment should start a weakening trend fairly soon. The weakening pace should accelerate on Sunday, and Aletta is expected to degenerate into a post-tropical remnant low by Tuesday. Aletta remains far away from any land areas.

To the east of Hurricane Aletta, Invest 92E has been designated by the National Hurricane Center (NHC). NHC gives 92E an 80 percent chance of development within 48 hours, and a 90 percent chance of development within five days. Virtually all of the global models predict development with 92E sometime this weekend, and 92E should be a tropical depression by Sunday. 92E is likely to take a track much closer to the Pacific coast of Mexico. Sea surface temperatures are expected to be very warm, and the environment around 92E is expected to be very moist. However, moderate wind shear may slow development. While this is still uncertain, the reliable ECMWF model has been consistent with 92E passing near the Baja California peninsula. The GFS model is slightly farther west. It is likely that if 92E were to affect the Baja California peninsula, cool sea surface temperatures could rapidly weaken the storm prior to reaching the region. The next name on the Eastern Pacific naming list is Bud.

The Atlantic basin continues to be quiet, with the NHC not expecting any tropical development during the next five days. However, the 12z GFS, CMC and ICON models continue to indicate the possibility that a low pressure area would form over the Northwestern Gulf of Caribbean and may organize as it enters the Gulf of Mexico. The 00z ECMWF model remained consistent with no development. The next name on the Atlantic naming list is Beryl.

I will be back with another post on the tropics tomorrow.