Weeks after floods killed dozens in Texas, residents are bracing for another round of threatening weather as Tropical Storm Bill bears down on the coast. (Reuters)

Update at 1:00 p.m.: Tropical Storm Bill officially made landfall on Matagorda Island in Texas at 11:45 a.m. central time, says the National Hurricane Center. Wind gusts up to 53 mph have been recorded at Palacios and Port O’Connor, and water levels were running about three feet above normal in Port Lavaca, close to the storm center.

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After being declared Tropical Storm Bill on Monday night by the National Hurricane Center, the highly-monitored disturbance in the Gulf of Mexico is making landfall Tuesday morning on the southern Texas coast, south of Houston near Port Lavaca. Though the storm is not boasting hurricane-force winds or an epic storm surge, it is expected to bring torrential rainfall to a region that has had little time to recover from its wettest month on record.

Radar image from Corpus Christi at 9:49 a.m. EDT, very close to landfall. (NOAA) Radar image from Corpus Christi at 9:49 a.m. EDT, very close to landfall. (NOAA)

On Monday night at 11 p.m. Eastern Time, the tropical disturbance was named Tropical Storm Bill, the second named storm of the season, having developed a well-organized closed surface low with sustained winds of 50 mph.

Since then, the tropical storm has continued to track northwest, approaching the central Texas coastline near Matagorda Island. The storm has strengthened a bit since Monday evening, with wind speeds increasing to 60 mph as it moves northwest at 13 mph.

Bill’s modest storm surge is pushing ashore north of the eye. The National Weather Service is expecting storm surge to remain at of below 3 feet above ground for most of the Texas coastline, from Sabine Lake south to Corpus Christi. However, the areas that are seeing the surge creep farthest inland are from around Freeport to Galveston.

Tropical Storm Bill may continue to at least maintain its current strength even after landfall, as the saturated soil across most of eastern Texas will act to delay the tropical storm’s weakening. This interesting scenario is what’s called a “brown ocean effect,” where the ground is so damp that the tropical cyclone can continue to draw moist energy from the surface despite not being over the ocean anymore.

In fact, the morning run of the NAM forecast model shows the system remaining quite healthy as it traverses Texas, Oklahoma and Missouri over the next two days. While it is certainly possible the model forecast is unrealistic, such an event would not be unprecedented. Tropical Storm Erin in 2007 reached peak intensity over central Oklahoma after making landfall very close to where Bill is making landfall this year.


Forecast from the 06Z NAM run showing simulated radar reflectivity and surface pressure contours. (tropicaltidbits.com)

As a tropical storm, Bill’s biggest threat by far is rainfall and the resulting flooding — actual damage from storm surge and wind should be minimal. In addition to the tropical storm warning in effect for much of the southeast Texas coast, a flash flood watch covers parts of seven states from Texas to Illinois.

bill-graphic

The five-day rainfall forecast from the National Weather Service continues to predict a significant amount of precipitation over eastern Texas and Oklahoma — nearly eight to 10 inches across eastern Texas. These rainfall totals will undoubtedly cause dangerous flash flooding and river flooding that may last multiple days.


Five-day accumulated rainfall forecast, valid from Tuesday morning through Sunday morning. (NOAA/WPC)

Beyond Thursday, Bill’s rainfall plume will continue to the northeast, reaching the Mid-Atlantic over the weekend. A snapshot from this morning’s GFS run shows a weak low pressure and associated rainfall over the northeast Sunday morning — this area is the remnant of Tropical Storm Bill. Rainfall totals in the Washington, D.C., area should remain moderate, perhaps one to three inches over the weekend with the highest totals north of the city.


Model forecast rainfall pattern during Sunday morning, from the 06Z GFS run today. (tropicaltidbits.com)