Residents along the Texas-Mexico border kept a watchful eye on Tropical Storm Dolly, stocking up on plywood, generators and flashlights as forecasters predicted the storm would strengthen into a hurricane later this week and make landfall.
Hurricane warnings were issued late Monday for parts of the Texas and Mexico coasts, meaning hurricane conditions were expected in those areas by the end of Tuesday.
The storm was expected to bring high winds and dump 10 to 20 inches (25 to 50 centimeters) of rain in coastal areas near the U.S.-Mexican border. Emergency officials feared major flooding problems and urged coastal residents to prepare.
Shell Oil said it was evacuating workers from oil rigs in the western Gulf Of Mexico, and the federal government was trying to decide whether they could begin construction on a new border fence, which was to be combined with levee improvements along the Rio Grande in Hidalgo County.
The National Hurricane Center in Miami issued a hurricane warning from Brownsville north to Port O'Connor. Meanwhile, a tropical storm warning was issued from Port O'Connor to the San Luis Pass, a strait south of Galveston.
Mexico also announced a hurricane warning from Rio San Fernando north to the U.S. border. A tropical storm warning and a hurricane watch were also in effect from La Pesca to Rio San Fernando.
Forecasters said Dolly was expected to make landfall late Tuesday or early Wednesday as a Category 1 hurricane, which has sustained winds of 74 mph (119 kph) to 95 mph (153 kph).
Texas officials said they would not order evacuations along the coast unless Dolly strengthens to a Category 3, with sustained winds of at least 111 mph (179 kph).
At 11 p.m. EDT Monday (0300 GMT Tuesday), the center of Tropical Storm Dolly was located about 435 miles (700 kilometers) southeast of Corpus Christi, Texas. It was moving at about 17 mph (27.4 kph) and had maximum sustained winds near 50 mph (80 kph). Tropical storm-force winds extended outward up to 200 miles (320 kilometers).
Dolly's winds were expected to strengthen Tuesday to hurricane force, which would mean at least 74 mph (119 kph).
Mexico discontinued its tropical storm warning for the Yucatan peninsula, which was battered by strong winds and drenched with rain a day earlier.
Texas Gov. Rick Perry activated 1,200 National Guard troops and other emergency crews. Mindful of the disastrous evacuation before Hurricane Rita hit the Texas Gulf Coast in 2005 - when far more people died from heat-related injuries and auto accidents fleeing the storm than from the severe weather - Perry also ordered 250 buses to be staged in San Antonio. The governor also ordered fuel teams to be ready to keep gas stations supplied and to help stranded motorists.
There are about 2 million people in the Rio Grande Valley, which includes the popular summer beach resort South Padre Island. Officials readied to evacuate residents in flood-prone areas and urged recreational vehicle owners on South Padre to head for higher ground.
"That amount of rain will present a big flooding problem for us," said Cameron County Emergency Management Coordinator Johnny Cavazos.
At a Home Depot in Brownsville near the border between the two countries, residents bought plywood, generators, batteries and flashlights, said store operations manager John Paul Martinez. He said a lot of people were just learning of Dolly, which became a tropical storm Sunday.
The federal government was to begin this week constructing the first part of the new border fence in Hidalgo County. While project supervisors met with emergency officials about the storm, large cranes unloaded steel beams and other supplies at a staging area near the levee Monday. Concrete walls will be incorporated into the river side of the levees to keep floodwaters, illegal immigrants and smugglers out.
The county is upgrading other levees and informed contractors Monday they should activate plans to prevent flooding, said Godfrey Garza, head of Hidalgo County Drainage District 1.
Meanwhile, Tropical Storm Cristobal was moving toward the east-northeast at about 16 mph (26 kph), away from the U.S. Cristobal was located about 360 miles (579 kilometers) east-northeast of Cape Hatteras, North Carolina, with maximum sustained winds near 60 mph (96 kph). Forecasters said the storm, which dumped rain on the coast of the Carolinas, was no longer an immediate threat to the U.S.
In the Pacific, Tropical Storm Genevieve formed off Mexico's coast, but forecasters said the storm was not expected to threaten land. Tropical Storm Fausto also was weakening and moving out to sea.
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