McALLEN, Texas — Texas mobilized National Guard troops and residents along the Gulf Coast near the Mexican border were buying plywood, flashlights and other supplies as Tropical Storm Dolly — expected by forecasters to strengthen into a hurricane this week — headed their way.

Hurricane warnings were issued late yesterday for parts of the Texas and Mexico coasts, meaning hurricane conditions were expected in those areas by the end of today.

Dolly was expected to make landfall later this week and bring with it high winds and 10 to 20 inches of rain in coastal areas. Emergency officials feared major flooding problems and urged coastal residents to prepare. Governor Rick Perry activated 1,200 National Guard troops and other emergency crews and Shell Oil said it was evacuating workers from oil rigs in the western Gulf Of Mexico.

Even as far up the coast as the Houston area, Harris County officials told residents to be ready in case the storm changes course and heads their way.

The National Hurricane Center at 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 American 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 today or early tomorrow as a Category 1 hurricane, which has with sustained winds of 74 mph to 95 mph.

Texas officials said they wouldn’t order evacuations along the coast unless Dolly strengthens to a Category 3, with sustained winds of at least 111 mph.

At 5 a.m. EDT today, the center of Tropical Storm Dolly was located about 295 miles southeast of Brownsville. It was moving west at about 15 mph and had maximum sustained winds near 60 mph. Tropical storm-force winds extended outward up to 160 miles.

Dolly’s winds were expected to strengthen today to hurricane force, which would mean at least 74 mph.

There are about 2 million people in the Rio Grande Valley, which includes popular summer beach resort South Padre Island. Officials readied to evacuate residents in flood-prone areas and urged RV owners on South Padre to head for higher ground.

“That amount of rain will present a big flooding problem for us,” the Cameron County Emergency management coordinator, Johnny Cavazos, said.

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 — Mr. Perry also ordered 250 buses to be staged at San Antonio. He also ordered fuel teams to be ready to keep gas stations supplied and to help stranded motorists.

In the Houston area yesterday, Harris County Judge Ed Emmett asked residents of the state’s most populous county to keep their gas tanks full, stock up on supplies and make sure they have plans ready to either evacuate or ride out a storm.

At a Home Depot at Brownsville near the border between the two countries, residents bought plywood, generators, batteries and flashlights, the store operations manager, John Paul Martinez, said. He said a lot of people were just learning of Dolly, which became a tropical storm Sunday.

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 at 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, the head of Hidalgo County Drainage District 1, Godfrey Garza, said.

Meanwhile, Tropical Storm Cristobal was moving toward the northeast at about 21 mph, away from the U.S. Cristobal was located about 485 miles northeast of Cape Hatteras, N.C., with maximum sustained winds near 60 mph. Forecasters said the storm, which dumped rain on the coast of the Carolinas, was no longer an immediate threat to America.

In the Pacific, Tropical Storm Genevieve strengthened slightly off Mexico’s coast, but forecasters said the storm was not expected to threaten land. Tropical Storm Fausto, which had been a hurricane, also was weakening and moving out to sea.