HOUSTON -- The heavy rains from Tropical Depression Allison that drenched Houston since Tuesday, continued their assault Friday and into Saturday morning prompting flood warnings from the National Weather Service.

The National Weather Service issued a flood warning for Fort Bend and Brazoria counties until 6:45 a.m., for Harris County until 8:45 a.m., for Montgomery County until 7 a.m. and for Waller and Grimes until 7:15 a.m.

Rising water forced officials to close down the following streets, highways and farm-to-market-roads:

Southwest Freeway at Westpark

East Loop at Market

HOV Gulf Freeway

FM 2850

North Loop 336

I-45 at Gladstell

Highway 10 at South Tollway

South Loop at Scott

I-10 East Wayside at McCarty

290 Pinemont at Hollister

I-45 along the Conroe area

297

League Line Road

105 West

FM 1488

FM 1484

County Line Road

Highway 242 at I-45

105 East

Calvary Road between Walnut Cove and I-45

297 and I-45

FM 1488 West of 45

Willis Waukegan from 1484 to 105

Highway 242 and I-45

Sam Houston Tollway eastbound exit to Ella Blvd.

All exit ramps in both directions on the Hardy Toll Road

Beltway 8 at Hardy Toll Road

Greens, Halls, Hunting and Sims Bayou in Harris County are close to reaching capacity at 11:30 p.m. Officials said that they are concerned with a stretch of the bayou west of Highway 288.

Hunting Bayou reached its capacity and officials said that they are concerned with the bayou near the 610 Loop and LBJ Hospital.

Halls Bayou has not risen above its banks, however officials said that they are keeping an eye on the bayou at Jensen.

Greens Bayou has not risen above its banks, however officials said that they are worried about the bayou near Mount Houston.

Reliant HL&P reported that 21,000 customers from Channelview to Fort Bend County and Humble were without power.

Leticia Lowe, spokeswoman for Reliant HL&P, said that customers in downtown and the Medical Center may also experience some power outage.

"Some areas will just have to wait until the water recedes before our crews can get to them," Lowe said. "Water and electricity don't mix."

There are also live wires down at the Southwest Freeway and Hazard, Lowe said.

In response to the mass flooding, Gov. Rick Perry asked the National Guard to be on alert. More than 120 troops and 25 military trucks will come to Houston if the city of Houston requests the help.

Chief Meteorologist Frank Billingsley said that the weekend will continue to be wet because the storm is trapped between two fronts.

Allison's Friday Movement

Allison's center shifted to the southwest and Friday morning was located 15 miles south of College Station, Texas, in Brazos County.

The heaviest rain occurred in the southeastern part of the Houston area. Thunderstorms and heavy showers were seen in Galveston and Liberties counties, and more than 5 inches of rain fell in southern Brazoria County.

Liberty County Emergency Coordinator Roy Hanel said that heavy rains forced the closure of several roads in the county.

There is also the possibility that Allison could end up strengthening over the weekend.

"The Gulf of Mexico is getting a little bit active," meteorologist Chuck George said. "And it looks as though an area of low pressure is going to form some place in the northern Gulf of Mexico, right along the Texas Gulf Coast."

Allison could possibly drift further south with the help of a high-pressure system that is moving in from the north.

The storm could be pushed back out over water and combine with the low-pressure system that is forming in the Gulf of Mexico, and could possibly come back up again as a tropical storm.

Flash Flood Watch Issued

The National Weather Service issued a flash flood watch is in effect for all of southeast Texas until 7 a.m. Saturday, for the following counties: Austin, Brazos, Brazoria, Burleson, Chambers, Colorado, Fort Bend, Galveston, Grimes, Harris, Houston, Jackson, Liberty, Madison, Matagorda, Montgomery, Polk, San Jacinto, Trinity, Waller, Walker, Washington and Wharton.

The threat of very heavy rains will continue on Saturday, as more of the region will be to the east and northeast of the circulation center.

A large swath of heavy rains from north to south across the area is very likely, and this may lead to very dangerous flooding.

Since large portions of southeast Texas have grounds that are already saturated from Allison-associated rainfall over the past four days, this additional heavy rainfall will lead to more deep standing water and overflows of small streams, creeks and bayous across southeast Texas.

The University of Houston Downtown and Texas Women's University canceled Saturday classes.

Bayou Flooding Rescues

The storm produced 4 to 5 inches of rain over the upper portions of the Sims Bayou in southwest Houston Thursday morning, forcing flooding above Hiram Clarke Road to below Telephone Road, near Hobby Airport.

Firefighters used rescue boats to help several people who were stranded by the rising waters along Sims Bayou. One of the victims rescued was a wheelchair-bound woman in the South Glen neighborhood.

City crews used large dump trucks to help carry dozens of people who were stranded by the high waters along the bayou.

Emergency officials said that about 170 people were rescued during the flooding.

Friday Houston Mayor Lee Brown said that 1,500 homes have been damaged from the three days of rain.

He said that 80 percent of the homes received minor damage, with 3 inches of water or less.

Brown has not decided if he will request a declaration of disaster from the federal government.

Disaster Centers, Shelters Opened

The Houston-area chapter of the American Red Cross set up four evacuation shelters for storm victims.

Berean 7th Day Adventist Church
2119 St. Emanuel
Houston, Texas

Jersey Village Baptist Church
16518 Jersey Drive
Houston, Texas

Atascasita Middle School
18180 West Lake Houston Parkway
Atascasita, Texas

Jamison Middle School
2506 Woody at FM 518
Pearland, Texas

Humble First Methodist Church
800 Main Street
Humble, Texas

McCullough Jr. High
3800 South Panther Creek
The Woodlands, Texas

Willis First Baptist Church
202 Thomanson
Willis, Texas

Second Baptist Church
10501 Muscantine
Jacinto City, Texas

St. Maximillian Colbe Catholic Church
10135 West Road
Houston, Texas

Jackson Intermediate School
1020 East Thimas
Pasadena, Texas

Friendswood Activity Center
416 Morningside
Friendswood, Texas

City of Houston Sunnyside Multi-Service Center
4605 Wilmington
Serving Southeast Houston

For more information on the American Red Cross, call (713) 526-8300 or (877) 725-0400 or log on to its Web site at www.houstonredcross.org, and then click on the Tropical Storm Allison link.