'Texas has never seen an event like' Harvey, FEMA chief says

Swollen rivers in east Texas aren't expected to crest until later this week, but federal officials are already predicting Tropical Storm Harvey will drive 30,000 people into shelters and spur 450,000 victims to seek some sort of disaster assistance.

And yet, forecasters say, more rain is coming. Lots more.

Several locales have already received 2 feet or more of rain, and forecasters say a reprieve won't arrive till week's end at the earliest. By then, rain totals could reach another 2 feet -- with isolated instances of 40 to 50 more inches -- along the upper Texas coast.

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"This is a landmark event for Texas," said FEMA Administrator Brock Long. "Texas has never seen an event like this."

But, Long warned, Harvey presents a dynamic situation, and "every number we put out right now is going to change in 30 minutes."

Harvey will likely surpass 2008's Hurricane Ike and 2001's Tropical Storm Allison, two of the most destructive storms to hit the Gulf coast in recent memory, he said. Around 13 million people from Corpus Christi to New Orleans are under flood watches and warnings as of Monday morning as Harvey's storm bands repeatedly pummel the same areas.

Early Monday, Harvey was just barely clinging to tropical storm status, but the danger is far from over. The storm is forecast to head back into the Gulf of Mexico and pick up additional moisture before sliding back over Galveston and Houston, cities it's already hammered.

Here are the latest developments:

-- The average annual rainfall in Houston is 50 inches. The city has seen 25 inches of rain in two days. Another 25 could fall by Saturday.

-- Several cities, including Alvin, Friendswood, League City, Pasadena, Pearland, Seabrook and Webster, have issued 11 p.m. curfews.

-- A mandatory evacuation order was issued for areas along the Brazos River in Fort Bend County.

-- Dallas is opening a "mega-shelter" capable of accommodating 5,000 evacuees at the Kay Bailey Hutchison Convention Center by Tuesday morning.

-- The Houston Independent School District has canceled school for the week.

-- President Donald Trump will travel to Texas on Tuesday, press secretary Sarah Huckabee Sanders said. Gov. Greg Abbott and Sen. John Cornyn, R-Texas, are scheduled to tour the coastal bend region Monday.

-- Energy provider CenterPoint says 96% of its Houston customers have power, but more than 87,000 are without electricity as the company's crews experience difficulty reaching the affected areas.

Houston volunteers

Reporter: We almost left, but heard your voice 05:28

Flooding continued in and around Houston on Sunday as citizens with boats assisted authorities in search and rescue efforts on roads that have turned into rivers.

A CNN crew was with one such volunteer when he used his vessel to rescue an elderly couple, their daughter and two dogs in Dickinson, Texas.

"It was shocking," daughter Pam Jones said of the floodwaters. "It just creeped up."

At Monday's press conference, Long encouraged more citizens to come forward, saying the rescue and recovery efforts would require community involvement. He said the National Voluntary Organizations Active in Disaster website would direct residents to religious and nongovernmental agencies through which residents can help out.

"It's going to require the citizens getting involved," Long said. "Donate your money. Figure out how you can get involved as we help Texas find a new normal."

An elderly couple was rescued by volunteers.

Houston resident Louise Walker told CNN she was trapped in her neighbor's apartment.

"Our bottom level is waist-deep in water. We have helicopters that are flying over us rescuing people, we have people who are living in these first-floor apartments like I have. They have been breaking into empty second level apartments just to have somewhere to go because we can't get out. We're simply completely surrounded with water," she said, adding that the helicopters were only rescuing people who were in immediate danger.

Nursing home residents rescued after waiting in several feet of water

"My only plan at this point is to stay out of the water. I've been keeping in contact with family and friends, but other than that we can't do anything. We are literally stuck here," Walker said.

Officials say they have conducted more than 250 water rescues and rescued more than 1,000 people. The US Coast Guard's Captain Kevin Odditt says 19 Coast Guard helicopters are also involved in relief efforts.

As of Sunday evening, between 800 and 1,200 people had been rescued from their homes in Galveston County, County Judge Mark Henry said.

An additional 1,000 National Guard members are being called in to help flood victims in Houston, Texas Gov. Greg Abbott announced via Twitter Sunday evening.