America's most flood-vulnerable county is preparing for a major influx of rain. 

Houston, Texas, is preparing for what could be catastrophic flooding, as severe downpours and extreme weather pound throughout the area. 

Flood watch advisories are in effect in several Houston counties, including Harris, Liberty, and Montgomery counties, after additional rounds of overnight storms battered the greater Houston metro area, reported Houston Public Media.

National Weather Service forecasters say a low-pressure system is taking shape off the coast of Houston on Monday, which will drive a "plume" of wet weather into Southwest Texas over the next few days, according to CHRON. 

Flooding waterways will continue to be "very high" over the next few days, said Jeff Lindner, a meteorologist with the Harris County Flood Control District, according to HPM. 

"It's very difficult to get the responses in the creeks, bodies, and rivers right if the rainfall that goes into them is not right," he explained. 

"So we struggled a lot this week with the rainfall forecast."

Harris County was recently named in a study as the nation's most vulnerable county when it comes to flooding.

LawnStarter took each county's risk and expected annual loss from riverine and coastal flooding into consideration for their research. Over 940 counties in the US, ranging from moderate to very high flood risk, were compared in accordance with FEMA. They also looked into the share of populations of children, elderly, and residents in mobile homes, in addition to local demand for flood insurance. 

Harris County officials said on Sunday that more than 200 people and 150 pets have been rescued in the floodwaters so far.

Looking across the nation, the study also shows that four counties in New Jersey fill out the top 5 most vulnerable areas. 

Bergen County, NJ, holds an overall score of 60.98, Ocean County, NJ, with 57.67, and Atlantic County, NJ, with 53.58.

Rounding out the top five is Cape May County, NJ, with 52.43.

Multiple counties in Florida were seen sporadically across the chart. 

New York, California, Kansas, and Kentucky claimed the last spots for the least number of state counties with a high risk of flooding.