Invest 99L in Western Caribbean a Threat to Develop on Monday

A tropical wave in the Western Caribbean was designated Invest 99L by the National Hurricane Center on Friday night, and is headed west-northwest at about 15 mph. Satellite loops on Saturday morning showed that 99L had a modest amount of spin and heavy thunderstorms, but these thunderstorms were poorly organized. Sea Surface Temperatures (SSTs) were very warm, near 29°C (84°F), and wind shear was moderate, 10 - 20 knots. Although these conditions are favorable for development, 99L will likely not have enough time to develop before crossing Mexico's Yucatan Peninsula on Sunday. The 8 am Saturday run of the SHIPS model predicted that conditions will be even more favorable for development on Monday when the wave will emerge in the Gulf of Mexico's Bay of Campeche. Wind shear will remain moderate, the atmosphere will be moister, and SSTs will be warmer: 29.5°C (85°F.) One of our three reliable computer models for predicting tropical storm formation, the GFS, showed some weak development occurring in the Bay of Campeche on Tuesday. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave 99L 2-day and 5-day development odds of 10% and 40%, respectively. The semi-circular ring of high terrain along the southern edge of the Bay of Campeche is known to aid in generating the counter-clockwise spiraling winds needed to assist in spinning up a new tropical storm, and given the propensity of tropical storms to quickly spin up in the Bay of Campeche, I'd put the 5-day development odds at 50%. If a tropical storm does form in the Bay of Campeche, the most likely track would be to the west-northwest or northwest towards the Mexican coast south of Texas. An Air Force hurricane hunter aircraft has been tasked to investigate 99L on Monday afternoon, if necessary.


Figure 1. Latest satellite image of Invest 99L in the Western Caribbean.

Jeff Masters