99L

Chances of Tropical Formation for 99L Increase to 80%

As of 7 pm CDT on 8/19/22, the National Hurricane Center (NHC) gave a tropical disturbance in the Gulf an 80% chance of turning into a named storm today or tomorrow. They call this area of investigation “99L.” Two days ago, the NHC gave this only a 10% chance of developing. But it survived going over the rugged terrain of Central America and is now out over water again where conditions are favorable for development.

Satellite imagery indicates that showers and thunderstorms are getting better organized. Deep thunderstorms have developed near/over this low pressure center.

Satellite photo taken at noon Houston time on 8/18/22.

According to NHC, environmental conditions appear favorable for additional development, and a tropical depression could form as the system moves northwestward across the southwestern and western Gulf of Mexico as early as today. However, by Saturday night, NHC predicts the system will move inland over northeastern Mexico, which will end its chances of development.

Conditions that support continued development include light wind shear, a large plume of moisture and very warm sea surface temperatures.

Jeff Lindner, Harris County Meteorologist

Interests along the lower Texas coast should monitor the progress of this system. Regardless of development, this system could bring locally heavy rains to southern Texas over the weekend.

More Rain for Houston Expected

In the northern hemisphere, low-pressure systems like this one rotate counterclockwise. So as the system heads toward Brownsville, it will spin moisture up along the Texas Gulf coast. That’s part of the reason why our rain chances for the next few days will remain high.

From Weather Live as of 12:40pm, 8/18/22.

As moisture from 99L spreads northward, it will interact with an incoming frontal boundary from the north and northwest early next week. That will also enhance rainfall chances.

Areas where Precipitable Water in atmosphere exceeds 1.5″. Precipitable waters are defined as the amount of water vapor in a column of air. Source: NWS Storm Prediction Center.

The National Weather Service’s Weather Prediction Center calls for another 4-5 inches of rain during the next 7 days.

Expected rainfall totals through 8/27/2022

Evening Update

As of 6:34 pm Houston time, NHC has increased the chances of formation to 80% and has started referring to the storm in the Gulf as “potential tropical cyclone #4.” Hurricane Hunter aircraft this afternoon did not find closed circulation. The plane did find an area of 25-30kt winds well to the northeast of the weak wind field near the active thunderstorms. The system is morning NW at around 15mph. Lindner expects the storm to make landfall as a 45 mph tropical storm tomorrow evening near the Rio Grande.

For more information, including the expected arrival time of tropical storm force winds, warning cones, and wind-speed probabilities, click here.

Conditions are changing rapidly. For the latest updates, monitor the National Hurricane Center website. During hurricane season, I bookmark this page and have it readily available on my phone.

Posted by Bob Rehak on 8/18/2022

1816 Days since Hurricane Harvey