Tropical disturbance 92L in the southern Gulf of Mexico’s Bay of Campeche was spreading heavy rains over southern Mexico and Central America on Wednesday, and it has the potential to develop into Tropical Storm Claudette by Friday. Regardless of development, 92L will bring heavy rains and dangerous flash flooding to the central U.S. Gulf Coast beginning on Friday.

On Wednesday morning, 92L was meandering near the coast of Mexico. The system had favorable conditions for development, with warm waters of 28-28.5 degrees Celsius (82-83°F), moderate wind shear of 10-15 knots, and a very moist atmosphere with a relative humidity at mid-levels of 80%. Satellite loops showed 92L with a broad circulation, but poorly organized and with limited heavy thunderstorms.

Figure 1
Figure 1. Satellite-estimated precipitation amounts over Mexico and Central America for the 24 hours ending at 8 a.m. EDT June 16, 2021, showed widespread rainfall amounts of 3-6 inches (yellow colors) with two areas of 10+ inches (red). (Image credit: Conagua)

Forecast for 92L

Steering currents are expected to push 92L slowly northwards at about 5 mph beginning Thursday night. The system will then accelerate, which should result in a landfall over the central or northwest U.S. Gulf Coast by Saturday. The landfall location of 92L could range anywhere from the Upper Texas coast to the Alabama/Florida border, according to the 6Z Wednesday run of the GFS ensemble model (Figure 2). However, the exact landfall location of 92L’s center is relatively unimportant, since heavy rain will be the storm’s main threat, and a wide swath of heavy rain will affect the central Gulf Coast regardless of 92L’s track.

Satellite measurements of total precipitable water (the amount of rain that would fall in a column of air if all the liquid, solid, and condensed water vapor fell as rain) showed 92L embedded in a very moist tropical airmass. This moisture will begin moving inland over the central U.S. Gulf Coast on Friday. Even if 92L does not develop into a tropical cyclone, its slow forward motion and high level of moisture likely will lead to rainfall amounts of 5-10 inches along the coast June 18 through June 20, causing damaging flash flooding. Already, soil moisture as of Tuesday, June 15, ranked in the top 1-5% of climatology for the date across the region likely to see 92L’s heaviest rains.

As 92L moves northwards over the Gulf, it will encounter cooler waters, increased wind shear, and drier air. Given 92L’s current disorganized state, these conditions suggest that the strongest 92L will get before landfall is a 60-mph tropical storm. A landfall of weaker intensity is more likely.

Figure 2
Figure 2. Potential position and intensity* of 92L at 8 a.m. EDT (12Z) Saturday, June 19, from the 6Z Wednesday, June 16, run of the GFS ensemble model (GEFS). The GEFS model includes 31 separate runs of the GFS model at lower resolution, each with slightly different initial conditions, intended to provide a measure of forecast uncertainty. Potential landfall locations of 92L ranged from the Upper Texas coast to Alabama. (Image credit: Tropical Tidbits)

*Predicted locations of centers of low pressure are shown as orange numbers in millibars, with the leading “10” or “9” omitted, depending on whether each low’s central pressure was above or below 1000 mb. For example, a 999-mb low pressure center will be displayed as “99”, and a 1000-mb low pressure system will be displayed as “00”. In blue numbers, with the leading “10” left off, are the predicted locations of centers of high pressure. For example, a 1020-mb high pressure system will be coded as “20”. Each of the 31 forecasts from the individual members generated a different location and central pressure for major high- or low-pressure systems. The color-coding is a measure (in standard deviations) of ensemble spread – the difference in pressure between the ensemble mean and the individual members.

Figure 3
Figure 3. Predicted seven-day rainfall amounts ending at 12Z Wednesday, June 22. The central Gulf Coast is predicted to receive 5-10 inches of rain from 92L. (Image credit: NOAA)

There is strong model support for development of 92L into a tropical depression by Friday, when it will be over the northern Gulf of Mexico. In an 8 a.m. EDT Wednesday tropical weather outlook, the National Hurricane Center gave 92L 2 two-day and five-day odds of development of 70% and 90%, respectively. The next name on the Atlantic list of storms is Claudette.

No other Atlantic tropical threats

Tropical Storm Bill lasted just 24 hours as a named storm, transitioning into a powerful extratropical storm with 50 mph winds on Tuesday night in the waters a few hundred miles southwest of Newfoundland, Canada. Cape Race, Newfoundland, recorded peak winds of 28 mph, gusting to 35 mph, at 4:30 p.m. local time as Bill approached. Bill had no significant impacts to land areas, and its name will be recycled and used again in the year 2027.

The tropical wave designated 94L off the coast of Africa has grown very disorganized, and is no longer being mentioned in NHC’s Tropical Weather Outlook.

Bob Henson contributed to this post.

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Jeff Masters, Ph.D., worked as a hurricane scientist with the NOAA Hurricane Hunters from 1986-1990. After a near-fatal flight into category 5 Hurricane Hugo, he left the Hurricane Hunters to pursue a...