A developing tropical disturbance is poised to soak much of South Texas with heavy flooding rains. Widespread totals of 5 to 10 inches are likely, with localized amounts up to 15 inches, and tropical-storm-force winds and at least some coastal splash-over and ocean surge are expected, as well.
Tropical storm warnings have been hoisted in Texas from San Luis Pass, which is just south of Galveston, southward to the mouth of the Rio Grande, and blanket a large section of coastal Mexico, too. Rockport, Corpus Christi and South Padre Island are included.
While this system could strengthen enough to become “Alberto,” there’s a chance it never technically meets the stringent requirements necessary to earn a name. Nonetheless, it’s still going to unleash all the staples of a tropical storm, with 35 to 45 mph winds and accompanying coastal and inland flooding.
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The same upper-air disturbance responsible for generating this “potential tropical cyclone” could spawn another one, also over the Gulf of Mexico, in the next seven days. There is also a third nascent disturbance over the northwestern Bahamas that could become something to watch for Florida or the Carolinas by later in the week.
Hurricane season historically peaks around Sept. 15, and this season is forecast to be unusually active. Favorable upper-level winds stemming from a developing La Niña pattern are predicted to couple with exceptionally warm Atlantic waters to produce both more, and more intense, storms.
The rainstorm to affect Texas
At 5 p.m. Eastern, Potential Tropical Cyclone 1 was 395 miles southeast of Brownsville, Tex. The designation “potential tropical cyclone” simply means that a system isn’t a tropical storm yet but is expected to bring tropical storm impacts. It allows the National Hurricane Center to issue watches and warnings before a system has technically formed. The system is moving north at 6 mph.
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It has winds up to 40 mph, but those winds are displaced far north of the center — atypical of a tropical cyclone. The system doesn’t have a well-defined center of circulation, either, nor a cohesive mass of convection, or shower and thunderstorm activity.
The setup
A large-scale area of scattered showers and thunderstorms is present over the southwestern Gulf of Mexico, western Caribbean and parts of Central America, including the Yucatán Peninsula. Meteorologists call this the CAG, or Central American Gyre. It’s a broad, diffuse zone of spin and weak low pressure.
Some weather models indicate that a more concentrated lobe of spin may consolidate and make landfall Wednesday night in Tamaulipas or Veracruz, Mexico, as a low-end tropical storm. Potentially more disruptive, however, will be the rich fetch of extreme moisture steered into Texas by the system.
Timing and impacts
Southeasterly winds will aim a robust tropical fire hose of moisture at Texas. Atmospheric moisture levels could approach an all-time record in Brownsville, Tex. The stage is set for an 18-to-24-hour period of torrential tropical downpours. Rainfall rates may exceed 2 inches per hour in the heavier rain bands.
It now looks like the heaviest rain will stay mainly south of Houston, though the city could see a general 3 to 6 inches of rain, with localized greater amounts. Houston, Galveston and the Golden Triangle are in a flood watch. (There will probably be a sharp northern cutoff to the heaviest rain, so it’s possible that those regions see markedly less than currently advertised.)
Farther south, amounts will be greater. That means Corpus Christi, Brownsville and McAllen could wind up with 5 to 10 inches, and perhaps more in a couple of spots.
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Winds of 35 to 45 mph will buffet the coastline, mainly from Galveston southward. That will push water against the coast, leading to a 2-to-4-foot surge, or storm-driven rise in water above normally dry land along the coast, from the Louisiana border to Sargent, Tex., including Houston and Galveston.
Rain and wind will arrive overnight Tuesday night and become heaviest Wednesday. By Wednesday evening, it will taper down in northern areas, though far South Texas will hold onto heavy downpours into early Thursday.
The system will also bring very heavy rain to northeast Mexico and Central America. “This rainfall will likely produce considerable flash and urban flooding along with new and renewed river flooding,” the National Hurricane Center said. Mudslides are also possible in the higher terrain in this region.
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The system should dissipate by Friday.
Another system to watch for in the southeast
A weak zone of low pressure, cloudiness and showers a few hundred miles east of the Bahamas will continue moving west. The broad atmospheric environment is just marginally conducive to development, meaning it probably won’t become a tropical depression or storm. The National Hurricane Center estimates only a 20 percent chance of eventual development before it moves ashore late in the week in the southeastern United States. It could bring some gusty showers near where it crosses the coast, but its exact path is uncertain.
