Invest 99L a Potential Threat to Western and Central Gulf Coast

A tropical wave in the southern Caribbean (Invest 99L) has a high chance of sparking tropical cyclogenesis in the northwest Caribbean late this week/this weekend.

Invest 99L is expected to cause a broad area of low pressure to develop in the southwest Caribbean tomorrow. This low will move into the northwest Caribbean Friday, and the southern Gulf of Mexico by Saturday.

Conditions are forecast to be favorable for development then, and a tropical cyclone is likely to form over the the northwest Caribbean or southern Gulf of Mexico. The National Hurricane Center is currently giving Invest 99L a high chance (80 percent) of developing into a tropical cyclone over the next 5 days.

Beyond this point things are less certain. Recent model guidance favors Invest 99L intensifying, possibly rapidly, over the western or central Gulf before hurricane making landfall in Texas or Louisiana late this weekend/early next week as a significant hurricane.

Latest GEFS tracks and MSLP for Invest 99L as of 18z Wednesday, August 25, 2021. (Image: Tropical Tidbits)

However, exact track/intensity remain unknown. The latest GFS ensembles (GEFS) illustrate this uncertainty. There is a large spread of possible tracks from south Texas to southwest Alabama.

What happens with Invest 99L in the Gulf will have a lot to do with how it evolves over the next 24 to 48 hours. For example, the operational GFS is much farther east compared to other models with the track of Invest 99L. It has landfall in southeast Louisiana Sunday. This appears to be because it has the center of Invest 99L forming farther north/east.

With regard to intensity, sea surface temperatures generally range from 30 to 31 degrees Celsius across most of the Gulf which is more than enough to support a strong/major hurricane.

The latest SHIPS intensity forecast has light wind shear and high mid-level relative humidity values as Invest 99L traverses the Gulf. If this comes to fruition, it could allow Invest 99L to take advantage of the warm sea surface temperatures.

It should also be noted that land interaction with the Yucatan Peninsula/western Cuba could also be an issue in the short term.

The bottom line is that, while uncertainty remains, it is becoming increasingly likely that Invest 99L will pose a threat to the Gulf Coast late this week/early next week. Interests along the western and central Gulf Coast should closely monitor its progress.

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For updates on the tropics you can also follow Hurricane Central and Daimien’s Gulf Coast Atlantic/Pacific Hurricane Tracking Center.

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Caleb Carmichael
Caleb Carmichael

Caleb is the owner of Gulf Coast Storm Center. He is currently an undergraduate student at Mississippi State University majoring in geoscience with a concentration in broadcast and operational meteorology. While not yet a meteorologist, Caleb has been providing weather updates, news, and analysis for the Gulf Coast since 2014.

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