HOUSTON, Sept. 11 (UPI) -- Hurricane Ike grew in size but not strength as it churned through the Gulf of Mexico Thursday toward the Texas coast, forecasters said.

Ike's shift toward the Houston area pushed emergency officials to call for a mandatory evacuation of residents in areas that would be affected by a storm surge, the Houston Chronicle reported.

Galveston, Texas, Mayor Lyda Ann Thomas expanded an evacuation order to include the entire island.

Harris County Judge Ed Emmett called for mandatory evacuations of low-lying areas and called on other Harris County residents to prepare to shelter in place.

"The winds will blow and they'll howl and we'll get a lot of rain, but if you lose power and need to leave, you can do that later,'' he said.

A hurricane warning was issued from Morgan City, La., to Baffin Bay, Texas, where hurricane conditions could reach by late Friday, the National Hurricane Center in Miami said.

Ike's center was about 580 miles east-southeast of Corpus Christi, Texas, and about 470 miles east-southeast of Galveston, the NHC said. The Category 2 hurricane, carrying sustained winds of 100 mph, was moving in a west-northwesterly direction at about 10 mph.

Hurricane-force winds extended 115 miles from Ike's center, the hurricane center said. Tropical storm-force winds were pushing out 275 miles.

Shelters in North Texas were preparing for the possibility of thousands of people fleeing the impact of Hurricane Ike along the Texas coast, The Dallas Morning News reported.

Texas Gov. Rick Perry put 7,500 National Guard members on standby and issued a disaster declaration for 88 counties, his office said. U.S. President George Bush declared an emergency in Texas, making federal funds available for the state to prepare for the storm.

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