Invest 90E over the Eastern Pacific has become a little better organized today as it moves west-northwestward through the tropical Pacific. The National Hurricane Center (NHC) gives 90E a 50 percent chance of development, both within 48 hours and five days. Scatterometer data from Tuesday afternoon indicates that the circulation has become much better defined, and an increase in convective organization will likely result in the formation of a tropical depression on Wednesday. 90E is no threat to land.

As of 18:00 UTC Tuesday, Invest 90E was centered near 10.4°N 121.0°W, and was moving generally west-northwestward. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1008 mb. 90E has only about 36-48 hours to develop before upper-level winds become unfavorable later this week. During the next 48 hours, wind shear is expected to be fairly low based on the SHIPS model (less than 15 knots), the mid-levels will remain moist (relative humidity around 70 percent), and sea surface temperatures will be above 27°C (80.6°F). On Friday, wind shear is expected to increase to around 25 knots, and sea surface temperatures will drop to about 26°C (78.8°F) as 90E moves into a drier and more stable environment.

It is interesting to note that most of the 12z Tuesday global models have significantly backed off with development of 90E. The 12z UKMET and ECMWF model runs predicted that 90E may not even become a tropical storm. The 12z Tuesday GFS model run continued to predict that 90E would develop into a moderate tropical storm, but it had backed off on intensity compared to Monday. Because the window of favorable conditions is expected to close by late Thursday, it appears unlikely that 90E will develop into anything more than a weak to moderate tropical storm.

I will be back with an update on 90E tomorrow afternoon, in which case a tropical cyclone may have formed. If 90E becomes a tropical storm, it would be named Aletta. If 90E develops into a tropical cyclone before 18:00 UTC tomorrow, it will set the record for the earliest tropical cyclone in the eastern Pacific proper – just set by Tropical Storm Adrian last year.