Tropical Alberto forms while bringing flooding rains and an ocean surge to Texas

The storm is forecast to make landfall in northeast Mexico Thursday morning while spreading impacts as far north as coastal Louisiana.

It’s the United States’ first taste of tropical trouble, but experts are calling for a long, busy season with many more threats on the way.

While approaching the coast of northeast Mexico, the potential tropical storm was also pushing a surge of ocean water ashore, leading to coastal flooding along the southern Texas coast early Wednesday. Social media video showed water inundating coastal communities, flowing over roads and underneath elevated homes while overwhelming storms drains.

Forecasters at the National Hurricane Center said the peak storm surge could reach up to 2 to 4 feet, including around Galveston Bay.

Flood watches blanket South Texas and the Rio Grande Valley, and stretch along the coastline to Cameron Parish, La. The alerts no longer include Houston, since the heaviest rains should stay primarily south of the metro.

A tropical storm warning does, however, cover coastal counties from just south of Galveston to the U.S.-Mexico border, and incudes Rockport, Corpus Christi and Brownsville. While the system may not organize enough to earn the name Alberto, tropical storm-force winds with 50-mph gusts are still probable along the shoreline.

Rockport was gusting to 36 mph around 7 a.m. Central time, and Padre Island to 39 mph. Rainfall totals have been light thus far, with Brownsville leading the pack at 0.95 inches. That said, the core of the deep tropical moisture, and subsequent downpours, will soon arrive.

As of 10 a.m. Central time, Alberto had maximum sustained winds of 40 mph and was moving west at 8 mph. The Hurricane Center said Alberto is a large tropical storm with tropical-storm-force winds extending up to 415 miles north of the center.

Scattered downpours were pivoting ashore in South Texas, and will become more numerous and intense as the day wears on. The heaviest rains will last from noon to midnight in southern regions, and probably won’t make it much north of San Antonio or Victoria.

A widespread 4 to 8 inches is likely in South Texas, with localized totals over 10 inches possible. Downpours will taper to intermittent showers by early Thursday.

A near record-moist air mass will be in place, allowing for intense rainfall rates. A weather balloon launched Wednesday morning from Brownsville recorded 2.78 inches of moisture present from the bottom to the top of the atmosphere. That’s just shy of the 2.93-inch record set on July 17, 1996.

Some of the storm’s most serious flooding is probable in northeast Mexico and Central America.

“Life-threatening flooding and mudslides are likely in and near areas of higher terrain across the Mexican states of Coahuila, Nuevo Leon, and Tamaulipas, including the cities of Monterrey and Ciudad Victoria,” the Hurricane Center wrote.

However, some of the rainfall in Mexico will be quite beneficial, as the area has been enduring serious drought.

Rains from a large, swirling area of showers and thunderstorms across the southwest Gulf of Mexico and Central America, known as the Central American Gyre, have produced disastrous flooding in parts Guatemala and El Salvador, causing at least 14 fatalities, according to the Associated Press. This same gyre spawned the potential tropical storm heading into Mexico and could give rise another in the Gulf of Mexico next week.

It’s still looking like 40- to 50-mph gusts will be possible along the immediate coastline from Houston-Galveston southward, with lesser but still blustery winds expected inland.

The onshore flow will push water against the coast, leading to a surge of up to 2 to 4 feet in the most prone areas and 1 to 3 feet elsewhere. Because of the system’s sprawling circulation, the surge was forecast to affect areas hundreds of miles from its center, as far away as the western shore of Louisiana.

With landfalling tropical cyclones and disturbances, sporadic tornadoes sometimes occur ahead, and to the right, of the center. Since South Texas will be in the “front right quadrant” of the system, a subtle change of low-level winds with height, known as wind shear, could support an isolated tornado risk.

The National Weather Service Storm Prediction Center has advertised a Level 1 out of 5 Marginal risk for severe weather.

Jason Samenow contributed to this report.