Weather officials downgraded Hurricane Harvey to a tropical storm this afternoon. It was a Category 4 storm when it made landfall at 10 p.m. Central on Friday night, but weakened to a Category 1 storm with 75 mph winds late Saturday morning. The National Weather Service is warning of devastating flooding and potential tornadoes.

The storm is now moving slowly and forecasters predict it will continue to dump as much as three feet of rainfall on the area in the coming days.

Seven-day rainfall forecast

as of August 26

0

20 inches or more

TEXAS

LA.

Predicted location

Thursday

Austin

Beaumont

Houston

San Antonio

Galveston

Saturday

Tuesday

15

Corpus Christi

Harvey’s

path

20 in.

Gulf of Mexico

100 MILES

MEXICO

Predicted location

Thursday

Louisiana

TEXAS

Austin

Beaumont

Houston

San Antonio

Sunday

Galveston

Saturday

Tuesday

Gulf of Mexico

Corpus Christi

Harvey’s

path

Laredo

Seven-day rainfall forecast

as of August 26

100 MILES

0

20 inches or more

LOUISIANA

TEXAS

Predicted location

Thursday

Baton Rouge

Austin

Lafayette

Beaumont

New Orleans

Houston

San Antonio

Wednesday

Sunday

Galveston

Victoria

Saturday

Tuesday

Monday

Rockport

Corpus Christi

Gulf of Mexico

Harvey’s path

Laredo

Seven-day rainfall forecast as of August 26

0

20 inches or more

100 MILES

The area of southeast Texas the storm is over is home to 7 million people. The counties at risk, which stretch along the Gulf Coast, have added 1.4 million residents since Hurricane Rita hit the state in 2005. The last major strike in Corpus Christi was Hurricane Celia in 1970.

It has been more than 50 years since Texas experienced a Category 4 storm, when Hurricane Carla made landfall in 1961.

Hurricane paths

Category 5

Category 4

Category 3

Category 2

Category 1

Tropical Storm

Population density

Less

More

Austin

TEXAS

Houston

San Antonio

Victoria

Rockport

Corpus Christi

Laredo

Gulf of

Mexico

50 MILES

Hurricane paths

Category 3

Category 1

Category 5

Population density

Category 2

Tropical Storm

Less

More

Category 4

50 MILES

Austin

Beaumont

Atascocita

LA.

Baytown

Port Arthur

Houston

New Braunfels

San Antonio

Pearland

League City

TEXAS

Victoria

Slow-moving Harvey

brings flooding rain

as of 10 a.m. Saturday

Rockport

Corpus Christi

Laredo

Gulf of

Mexico

MEX.

50 MILES

Lake Charles

Austin

Beaumont

Atascocita

LOUISIANA

Port Arthur

Houston

New Braunfels

Baytown

League City

San Antonio

Pearland

TEXAS

Red Cross Shelters

open Saturday

Victoria

Slow-moving Harvey

brings flooding rain

as of 10 a.m. Saturday

Rockport

Corpus Christi

Laredo

Hurricane

paths

Gulf of Mexico

Category 5

Category 4

Category 3

MEXICO

Category 2

Population density

Category 1

Less

More

Tropical Storm

McAllen

 

On Thursday, as Harvey headed toward the coast, Texas Gov. Greg Abbott (R) declared a preemptive state of disaster in 30 counties, including Harris County, home to Houston, the fourth-most-populated city in the country.

On Friday night, President Trump signed a disaster proclamation to provide immediate aid.

In this video, Capital Weather Gang's Angela Fritz explains why Harvey will have an effect for days after making landfall on the Texas coast:

Even small storms that carry a lot of rain can be dangerous. In 2001, Tropical Storm Allison looped over Houston and dropped 28 inches of rain in 12 hours on one neighborhood, causing 22 deaths and $5 billion in damage.

Houston is low and swampy, so whatever rain falls there has to filter out through the city’s bayou network.

As the city’s population grew, developers built structures over large chunks of wetlands, leaving the vulnerable land with less natural drainage.

Rivers

Intermittent

Year-round

100 MILES

Austin

Houston

San Antonio

TEXAS

Gulf of

Mexico

Rockport

Area

of landfall

Corpus Christi

50 MILES

In Hill Country, an area known as Flash Flood Alley

is prone to flooding.

Austin

Houston

San Antonio

TEXAS

Gulf of Mexico

Victoria

Many rivers in South Texas are dry most of the time, only running after major rainstorms

Rivers

Intermittent

Rockport

Year-round

Area

of landfall

Corpus Christi

MEXICO

50 MILES

Lake Charles

Austin

Beaumont

In Hill Country, an area known as Flash Flood Alley

is prone to flooding.

Atascocita

LOUISIANA

Port Arthur

Houston

Baytown

New Braunfels

San Antonio

League City

Pearland

TEXAS

Victoria

Many rivers in South Texas are dry most of the time, only running after major rainstorms

Gulf of Mexico

Rockport

Rivers

Area

of landfall

Intermittent

Year-round

Corpus Christi

Laredo

MEXICO

The impermeable surfaces — asphalt and concrete — reduced the area’s ability to absorb excess water, which worsens flooding.

The storm’s assault on Texas is just getting started, disastrous inland flooding expected

Farther north in Central Texas, where the Hill Country meets the plains, the region has been nicknamed “Flash Flood Alley” because its topography makes it so susceptible to localized flooding. Air masses collide over the hills and form heavy, slow-moving rainstorms that send water rushing down the rocky terrain into areas between San Antonio and Austin.

The Gulf of Mexico is vital for the nation’s oil infrastructure.

Barrels per calendar day

(in thousands)

100

500

Austin

50 MILES

TEXAS

Oil refinery

Houston

San Antonio

Expected area

of landfall

Corpus Christi

Laredo

Pipeline

Offshore

platforms

MEXICO

Gulf of Mexico

Barrels per calendar day

100,000

500,000

LOUISIANA

50 MILES

Austin

Beaumont

Lafayette

TEXAS

Houston

Oil refinery

San Antonio

Galveston

Victoria

Expected area

of landfall

Corpus Christi

Laredo

Pipeline

Offshore

platforms

Gulf of Mexico

MEXICO

100 MILES

TEXAS

LOUISIANA

Austin

Lafayette

Beaumont

Houston

Oil refinery

San Antonio

Galveston

Victoria

Expected area

of landfall

Corpus Christi

Laredo

Barrels per calendar day

Pipeline

100,000

Offshore

platforms

500,000

Gulf of Mexico

MEXICO

Offshore platforms produce about 1.7 million barrels a day, nearly a fifth of U.S. crude oil production. More than 45 percent of U.S. petroleum refining capacity lies along the Gulf Coast, as well as 51 percent of total U.S. natural gas processing plant capacity, according to Energy Department data.

A network of rigs and pipelines in the Gulf have shut down in anticipation of the storm.

Houston is home to some of the biggest oil refineries in the U.S., and its busy shipping port has chemical and other factories that are an important part of the worldwide supply chain.

Bonnie Berkowitz and Dan Keating contributed to this report.

About this story

Disaster shelter data from American Red Cross. Population data from U.S. Census Bureau. Previous storm paths from National Hurricane Center and National Weather Service. Rivers data from U.S. Geological Survey. Rainfall forecast from the National Hurricane Center. Oil refinery data from the U.S. Energy Information Administration and U.S. Bureau of Ocean Energy Management.

Originally published Aug. 25, 2017.

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