Invest 91E over the eastern Pacific basin has become much better organized today, and is close to becoming a tropical depression. Satellite imagery indicates that the circulation is becoming better defined, although an ASCAT pass from Tuesday morning was inconclusive as to whether a well defined circulation had formed. The National Hurricane Center (NHC) gives 91E a near 100 percent chance of development within 48 hours. 91E is likely to have advisories initiated by tonight, should become Tropical Storm Aletta by Wednesday and probably a hurricane by the weekend. 91E is no major threat to land, with the exception of rip currents and swells along the Pacific coast of North America.

As of 18:00 UTC Tuesday, Invest 91E was centered near 13.5°N 105.0°W, and was moving slowly west-northwestward. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1007 mb. 91E is likely to become a tropical depression tonight and a tropical storm on Wednesday. All of the global models develop 91E within the next 24 hours. The SHIPS, HWRF, HMON and GFS models predict that 91E will become a hurricane by Saturday. The ECMWF model is weaker, but still predicts modest intensification with 91E. Since 91E is organizing faster than anticipated, I would lean to the more aggressive models at this time.

The environment around 91E is very conducive for intensification. Wind shear is expected to be light (less than 10 knots), mid-level relative humidity values are expected to be fairly moist, and sea surface temperatures are expected to remain above 27°C (80.6°F) for the next five days or so. With such a favorable environment, it would not be surprising to see 91E become a major (Category 3 or higher) hurricane by the weekend. The GFS model is quite extreme with intensification, deepening 91E to 924 mb by early Sunday. However, I think the GFS is likely overdoing intensity as it often does with tropical cyclones. By early next week, 91E should begin to weaken as it moves into cooler waters and a drier environment.

Behind 91E, the NHC is already monitoring another system for development. An area of low pressure is expected to form late this week south of the Gulf of Tehauntepec. Environmental conditions are expected to be conducive for development, and both the ECMWF and GFS models are indicating that this system could become a strong hurricane very close to the coast of Mexico. The second name on the 2018 Pacific hurricane season naming list is Bud.

The Atlantic basin remains quiet, with no development expected during the next 10 days. I will be back with an update on 91E tomorrow, which is likely to be a tropical cyclone by that time.