Oscar Peru of U.S. Customs and Border Protection searches for flood victims from a helicopter after torrential rains pounded the area on August 31, 2017 near Sugar Land, Texas. (Scott Olson/Getty Images)
This is a 'before' DigitalGlobe satellite imagery of Simonton, Texas, taken in November 2016. (DigitalGlobe via Getty Images)
This is an 'after' DigitalGlobe satellite imagery of Simonton, Texas on August 30, 2017. (DigitalGlobe via Getty Images)
In this Thursday, Aug. 31, 2017, photo, volunteers with the Islamic Society of Greater Houston package donations at a mosque that was being used as a shelter. (Jay Reeves/AP Photo)
Tyler Moody removes a mattress from a friend's home after floodwaters from Tropical Storm Harvey drenched the city Thursday, Aug. 31, 2017, in Houston. (Gregory Bull/AP Photo)
Liv Gilreath searches for salvageable items from a friend's home after floodwaters from Hurricane Harvey drenched the city, Thursday, Aug. 31, 2017, in Houston. (Gregory Bull/AP Photo)
Rescue workers begin mandatory evacuations in the area beneath the Barker Reservoir as water is released in Houston, Texas on August 31. (MARK RALSTON/AFP/Getty Images)
A viewer sent in these photos of the rescue of a bunny found struggling in the water. They said after several hours of caring for it, the bunny was able to hop away. (Sheryl Maiden)
A viewer sent in these photos of the rescue of a bunny found struggling in the water. They said after several hours of caring for it, the bunny was able to hop away. (Sheryl Maiden)
Monster trucks and other vehicles in Spring, Texas during rescue efforts. (Chris Stephens/Facebook)
A young girl in Mississippi overheard her parents talking about a trip to Houston, so she offered to donate her doll with a sweet note. Her parents are Hurricane Katrina survivors. (EJ Bice/Facebook)
Little JW Claburn welcomed the National Guard into his community, Rio Vista, with an American flag. JW will turn 5 on Sept. 6. (Emily Fearno Claburn/Facebook)
This dog is among the adoptable pets being sent to Atlanta to make room for rescued animals at the Houston SPCA. (Laura Anthony/KGO)
Deer navigate the flood waters near Clay Road and Queenston Blvd in Houston. (K.C.)
A resident of the Lake Olympia neighborhood in Houston sent in this photo of a baby alligator, writing, ''The mother must be close by!'' (Michelle Bass)
Volunteers sort through donations in this viewer-submitted photo. (Uyen Do)
Downtown Houston, Texas is reflected in flooded Buffalo Bayou Wednesday, Aug. 30, 2017, as the city continues to recover from record flooding caused by Hurricane Harvey. (Charlie Riedel/AP Photo)
Harvey flood evacuee Cyree Howard, 3, carries a ball through a shelter setup inside NRG Center Wednesday, Aug. 30, 2017, in Houston. (David J. Phillip/AP Photo)
Cyree Howard, 3, is comforted by his mother's hand while inside a shelter setup inside NRG Center for victims of Harvey Wednesday, Aug. 30, 2017, in Houston. (David J. Phillip/AP Photo)
(LM Otero/AP Photo)
Flood waters and pollution surround buildings in West Houston, TX on Wednesday, Aug 30, 2017. (Jabin Botsford/The Washington Post via Getty Images)
U.S. Border Patrol Agent Steven Blackburn, left, checks if people wading in water need help during a search a rescue operation in a neighborhood inundated by floodwaters. (LM Otero/AP Photo)
Harvey flood evacuee children look through donated shoes at a shelter setup inside NRG Center Wednesday, Aug. 30, 2017, in Houston. (David J. Phillip/AP Photo)
Gillis Leho looks for documents in her car that was covered by floodwaters brought on by Tropical Storm Harvey in Houston, Texas, Wednesday, Aug. 30, 2017. (LM Otero/AP Photo)
Flooded homes are shown near Lake Houston following Hurricane Harvey August 29, 2017 in Houston, Texas. (Win McNamee/Getty Images)
People watch as people are rescued ad brought to shore as flood waters surround houses and apartment complexes in West Houston, TX on Wednesday, Aug 30, 2017. (Jabin Botsford/The Washington Post via Getty Images)
Children play at a shelter setup inside NRG Center for flood victims of Harvey Wednesday, Aug. 30, 2017, in Houston. (David J. Phillip/AP Photo)
Citizen rescuers in Houston on Tuesday captured these photos. (Larry Brown/Twitter)
Citizen rescuers in Houston on Tuesday captured these photos. (Larry Brown/Twitter)
Citizen rescuers in Houston on Tuesday captured these photos. (Larry Brown/Twitter)
Barry Horvitz hugs his wife Kim while standing outside their home after removing items damaged by floodwaters from Tropical Storm Harvey on Wednesday, Aug. 30, 2017, in Houston. (David J. Phillip/AP Photo)
Jose Martinez, right, works to remove drywall from a home damaged by floodwaters from Tropical Storm Harvey Wednesday, Aug. 30, 2017, in Houston. (David J. Phillip/AP Photo)
Michael Saghian walks across the living room of his home damaged by floodwaters from Tropical Storm Harvey on Wednesday, Aug. 30, 2017, in Houston. (David J. Phillip/AP Photo)
A home is surrounded by floodwaters from Tropical Storm Harvey on Tuesday, Aug. 29, 2017, in Houston. (David J. Phillip/AP Photo)
Houston police patrol the downtown area as the first days curfew ends after Hurricane Harvey caused heavy flooding in Houston, Texas on August 30, 2017. (MARK RALSTON/AFP/Getty Images)
The sun rises over the downtown area as the first days curfew ends after Hurricane Harvey caused heavy flooding in Houston, Texas on August 30, 2017. (MARK RALSTON/AFP/Getty Images)
A human chain is formed during a rescue operation at I-10 and Federal Road in Houston. (M. Alvarez)
Glenda Montelongeo, Richard Martinez and his two sons are helped out of a boat after being rescued near Tidwell Road and Toll road 8 in Houston, TX on Tuesday. (Jabin Botsford/The Washington Post via Getty Images)
The Houston Police rescues a woman stranded by the flood. (houstonpolice/Twitter)
The Twitter user who posted this photo on Tuesday wrote, ''THE SUN IS OUT IN HOUSTON. I repeat. THE SUN IS OUT IN HOUSTON.'' (Gabby Greer)
The Harris County Sheriff posted this photo of residents rescued in a convoy while helping out with rescues on Tidwell Rd in Houston. (SheriffEd_HCSO/Twitter)
The Harris County Sheriff posted this photo on Tuesday while helping out with rescues on Tidwell Rd in Houston. (SheriffEd_HCSO/Twitter)
The Harris County Sheriff posted this photo on Tuesday while helping out with rescues on Tidwell Rd in Houston. (SheriffEd_HCSO/Twitter)
''#PhotosFromtheField: One team, one mission. #TMDHarvey #Harvey,'' the Texas Military Department posted on Twitter. (TXMilitary/Twitter)
The Houston Police rescues a dog stranded by the flood. (houstonpolice/Twitter)
These photos show the view from downtown Houston three days in a row. (Ctycksen/Twitter)
These photos show the view from downtown Houston three days in a row. (Ctycksen/Twitter)
''#PhotosFromtheField: One team, one mission. #TMDHarvey #Harvey,'' the Texas Military Department posted on Twitter. (TXMilitary/Twitter)
These photos show the view from downtown Houston three days in a row. (Ctycksen/Twitter)
The Houston Police rescue a group stranded by the flood. (houstonpolice/Twitter)
The Houston Police rescue a group stranded by the flood. (houstonpolice/Twitter)
Loved ones help put rain coats on children after they escaped a flooded neighborhood during the aftermath of Hurricane Harvey on August 29, 2017 in Houston, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)
Members of the US Coast Guard help residents leave a flooded residential area during the aftermath of Hurricane Harvey on August 29, 2017 in Houston, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)
People walk to a Harris County Sheriff air boat while escaping a flooded neighborhood during the aftermath of Hurricane Harvey on August 29, 2017 in Houston, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)
Volunteer Asuleni Santiago, 11, carries donated clothes for victims of the flooding from Tropical Storm Harvey at a shelter opened at the Lakewood Church in Houston on Tuesday. (LM Otero/AP Photo)
Highways around downtown Houston are empty as floodwaters from Tropical Storm Harvey overflow from the bayous around the city Tuesday, Aug. 29, 2017, in Houston. (David J. Phillip/AP Photo)
Volunteers Brenda Tcoc, right, and Hugo Wilson help sort bags of donated clothes for victims of the flooding after a shelter opened at the Lakewood Church on Tuesday. (LM Otero/AP Photo)
Harris County Constable Pct. 2 Christopher E. Diaz posted this photo searching for the mother of the baby found in Houston. They have since been reunited. (Constable Christopher Diaz)
People take shelter at Alief Taylor High School. (AliefISD/Twitter)
People take shelter at Alief Taylor High School. (AliefISD/Twitter)
Residents evacuate near the Addicks Reservoir as floodwaters from Tropical Storm Harvey rise Tuesday, Aug. 29, 2017, in Houston. (David J. Phillip/AP Photo)
Evacuees make their way though floodwaters near the Addicks Reservoir as floodwaters from Tropical Storm Harvey rise Tuesday, Aug. 29, 2017, in Houston. (David J. Phillip/AP Photo)
Evacuees are helped as floodwaters from Tropical Storm Harvey rise Tuesday, Aug. 29, 2017, in Houston. (David J. Phillip/AP Photo)
Homes are flooded near the Addicks Reservoir as floodwaters from Tropical Storm Harvey rise Tuesday, Aug. 29, 2017, in Houston. (David J. Phillip/AP Photo)
Vian Janse van Rensburg and his family in Katy, Texas, got their dogs to safety using what they had, an inflatable swan. (Mia Rensburg/Twitter)
Alexis Hernandez holds her daughter Faith as they make their way into the crowded George R. Brown Convention Center in Houston, Texas, on Tuesday, Aug. 29, 2017. (LM Otero/AP Photo)
A father is reunited with his children who were evacuated in the Clodine district after Hurricane Harvey caused heavy flooding in Houston, Texas on August 29, 2017. (MARK RALSTON/AFP/Getty Images)
Volunteer rescuers evacuate people from a flooded residential area during the aftermath of Hurricane Harvey on August 29, 2017 in Houston, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)
Rescue workers and volunteers help residents make their way out of a flooded neighborhood after it was inundated with rain water on August 29, 2017 in Houston. (Scott Olson/Getty Images)
''#PhotosFromTheField: 36th CAB @36thInfantryDiv in action during rescue operations in #Texas. #Harvey #TMDHarvey @USNationalGuard'' the Texas Military Department wrote. (TXMilitary/Twitter)
Ezekiel Lyons, left, walks with his wife at the George R. Brown Convention Center that has been set up as a shelter on Tuesday, Aug. 29, 2017. (LM Otero/AP Photo)
Robert Salgado, 2, sleeps on the floor at the George R. Brown Convention Center that has been set up as a shelter on Tuesday, Aug. 29, 2017. (LM Otero/AP Photo)
People rest at the George R. Brown Convention Center that has been set up as a shelter on Tuesday, Aug. 29, 2017. (LM Otero/AP Photo)
Benedict Lim and his son, Jacob Lim, delivered home-cooked food to neighbors on their inflatable kayak in this viewer-submitted photo from Houston. (Benedict Lim)
Koi from the Lone Star Koi Club swim around the flood waters in this viewer-submitted photo. The viewer wrote ''One of those sights that one would laugh and cry at the same time.'' (Nam Hoang)
A Coast Guard helicopter lowers someone in Houston, TX on Monday, Aug 28, 2017. (Jabin Botsford/The Washington Post via Getty Images)
Barb Davis, 74. is helped to dry land after being rescued from her flooded neighborhood after it was inundated with rain water, on August 28, 2017. (Scott Olson/Getty Images)
People move from helicopters to busses as they land on Highway 69 after being rescued in Houston, TX on Monday, Aug 28, 2017. (Jabin Botsford/The Washington Post via Getty Images)
A flood victim in a wheel chair is helped off a delivery truck after being rescued during Hurricane Harvey, Monday, August 28, 2017. (Juan DeLeon/Icon Sportswire via Getty Images)
People are rescued from a flooded neighborhood after it was inundated with rain water, remnants of Hurricane Harvey, on August 28, 2017 in Houston, Texas. (Scott Olson/Getty Images)
A man waves down a rescue crew as he tries to leave the area after it was inundated with flooding from Hurricane Harvey on August 28, 2017 in Houston, Texas. (Joe Raedle/Getty Images)
Rescue workers discovered southeast Houston resident Betty Walter sheltering 21 neighborhood dogs. Walter and the dogs were all rescued. (William Beasley)
''#PhotosFromTheField: #Evacuees and #NationalGuard take shelter in #Houston on 28 August, 2017. #Harvey'' wrote the Texas Military Department on Twitter. (TXMilitary)
A neighbor does not believe anyone was home in this burning building in Friendswood, Texas. Firefighters were unable to reach it. (alemley29/Instagram)
An explosion has rocked a building on Fannin Street in downtown Houston on Monday. (Chris Hisle/Twitter)
''Out of food and water for these 200+ people anything good would help!!!'' wrote Serena McDougle from 1st Bapt Church in North Houston. (Serena McDougle/Facebook)
A family in Houston posted this photo from their rescue. (Rosa Preciado Hernandez)
A 60-year-old female died in East Montgomery County when a tree fell on her while she slept, the sheriff's office confirmed. (MCTXSheriff/Twitter)
People are rescued from a hotel by boat after Hurricane Harvey caused heavy flooding in Houston, Texas on August 27, 2017. (MARK RALSTON/AFP/Getty Images)
Stranded vehicles sit where they got stuck in high water from Hurricane Harvey on Dairy Ashford Drive, August 28, 2017 in Houston, Texas. (Erich Schlegel/Getty)
The downtown Houston skyline and flooded highway 288 are seen August 27, 2017 as the city battles with tropical storm Harvey and resulting floods. (THOMAS B. SHEA/AFP/Getty Images)
Naomi Coto carries Simba on her shoulders as they evacuate their home after the area was inundated with flooding from Hurricane Harvey on August 27, 2017 in Houston, Texas. (Joe Raedle/Getty Images)
082717-ktrk-girl-sign-rescue-1-vid (KTRK)
People view the flooded highways in Houston on August 27, 2017 as the city battles with tropical storm Harvey and resulting floods. (THOMAS B. SHEA/AFP/Getty Images)
A man helps children across a flooded street as they evacuate their home after the area was inundated with flooding from Hurricane Harvey on August 27, 2017 in Houston, Texas. (Joe Raedle/Getty Images)
A charred, abandoned car is seen on Interstate 610 North August 27, 2017 in Houston as the city battles with tropical storm Harvey and resulting floods. (THOMAS B. SHEA/AFP/Getty Images)
People walk through the flooded waters of Telephone Rd. in Houston on August 27, 2017 as the US fourth city city battles with tropical storm Harvey and resulting floods. (THOMAS B. SHEA/AFP/Getty Images)
People push a truck down a flooded street after the area was inundated with flooding from Hurricane Harvey on August 27, 2017 in Houston, Texas. (Joe Raedle/Getty Images)
Residents are evacuated from their homes surrounded by floodwaters from Tropical Storm Harvey on Aug. 27, 2017 in Houston. (AP Photo/David J. Phillip)
Evacuees wade down a flooded section of Interstate 610 as floodwaters from Tropical Storm Harvey rise on Aug. 27, 2017 in Houston. (AP Photo/David J. Phillip)
Jayveon Murphy, 10, makes is way through floodwaters from Tropical Storm Harvey to check on a neighbor at his apartment complex in Houston on Aug. 27, 2017. (AP Photo/LM Otero)
Wilford Martinez, right, waits to be rescued by Harris County Sheriff's Dept. after his car got stuck in floodwaters on Aug. 27, 2017 in Houston. (AP Photo/David J. Phillip)
A man helps a woman in floodwaters from Tropical Storm Harvey on Aug. 27, 2017 in Houston. (AP Photo/David J. Phillip)
Residents are rescued from their homes surrounded by floodwaters from Tropical Storm Harvey on Aug. 27, 2017 in Houston. (AP Photo/David J. Phillip)
''View from the front door. #hurricaneharvey #hurricaneharvey2017 #rainraingoaway,'' wrote an Instagram user in Dickinson (sweetapplesnider/Instagram)
''About 3 feet of water in the house now. The cars are toast. Luckily we are safe. #prayfortexas #prayforhouston #hurricane #harvey,'' wrote
an Instagram user in Meyerland. (devinduoto/Instagram)
''#USCG Flood Punt Teams conducting urban search and rescue in greater #houston area. #Harvey,'' tweeted the US Coast Guard. (USCGHeartland/Twitter)
''#USCG Flood Punt Teams conducting urban search and rescue in greater #houston area. #Harvey,'' tweeted the US Coast Guard. (USCGHeartland/Twitter)
''Harris County Sheriff's Office deputies are out in the Blackhorse subdivision still working high water rescues,'' the office wrote on Facebook (Harris County Sheriff's Office/Facebook)
US Coast Guard Heartland Flood Punt Teams conducting urban search and rescue in the greater Houston area. (USCG Heartland)
US Coast Guard Heartland Flood Punt Teams conducting urban search and rescue in the greater Houston area. (USCG Heartland)
An airboat is used to rescue people from an apartment building. (Jenifer Woloson)
Texas National Guard rescues Texans from floodwaters in Houston area. (Texas Military Department)
Texas National Guard rescues Texans from floodwaters in Houston area. (Texas Military Department)
Texas National Guard rescues Texans from floodwaters in Houston area. (Texas Military Department)
Texas National Guard rescues Texans from floodwaters in Houston area. (Texas Military Department)
A flooded runway roads just outside Hobby Airport (Foti Kallergas)
Flooded runway and roads at Hobby Airport. (Foti Kallergis)
(Moni Bohnisch)
The Texas Military Department wrote, ''#BREAKINGNEWS: #Texas #NationalGuard are using every means available to save Texans in #Houston. #TMDHarvey #Harvey @USNationalGuard.'' (TXMilitary/Twitter)
The Texas Military Department wrote, ''#BREAKINGNEWS: #Texas #NationalGuard are using every means available to save Texans in #Houston. #TMDHarvey #Harvey @USNationalGuard.'' (TXMilitary/Twitter)
The Texas Military Department wrote, ''#BREAKINGNEWS: #Texas #NationalGuard are using every means available to save Texans in #Houston. #TMDHarvey #Harvey @USNationalGuard.'' (TXMilitary/Twitter)
The Texas Military Department wrote, ''#BREAKINGNEWS: #Texas #NationalGuard are using every means available to save Texans in #Houston. #TMDHarvey #Harvey @USNationalGuard.'' (TXMilitary/Twitter)
HOUSTON, Texas -- A flash flood emergency in Houston has displaced families, stranded motorists, and left many people wondering what might happen next.