Tropical Storm Nicholas is closing in on Texas, where a hurricane watch has been issued south of Galveston.

       Nicholas, now churning with 60 mph winds, could strengthen to a hurricane when it makes landfall Monday night between Corpus Christi and Galveston (hurricanes have 74 mph or higher winds).

       RAMMB/NOAA/NESDIS/AFP via Getty Images

       This NOAA satellite image shows Tropical Storm Nicholas, off the coastline of Texas on the morning of Sept. 13, 2021.

       Heavy rain, flash flooding, dangerous storm surge, isolated tornadoes and gusty winds are expected in Texas and Louisiana.

       The high risk areas stretch from Matagorda to Galveston to Port Arthur, where life-threatening flash flooding is possible. Rain totals are predicted to be between 6 and 12 inches to isolated maximum amounts of up to 20 inches, according to the latest forecast.

       MORE: Above-average Atlantic hurricane season predicted

       Gov. Greg Abbott issued a disaster declaration for 17 Texas counties and has prepped resources, including boat teams and rescue aircrafts, to assist any affected areas.

       In Houston, the heaviest rain will come Monday night, and flash flooding is possible.

       In Harris County, which encompasses Houston, Judge Lina Hidalgo warned Monday afternoon: "We could get 10 to 15 inches of rain over the next 24 hours or so -- and that would be very, very concerning."

       All public health testing and vaccination sites will stop operations in Harris County. Schools in Houston will be closed on Tuesday.

       "What I need each resident of this county to do today is to get to where you are going to be by 6 p.m. tonight and stay there," Hidalgo said.

       Jason Fochtman/Houston Chronicle via AP

       Paul Villagomez secures filled gas containers in his truck as he prepares for Tropical Storm Nicholas, Sept. 13, 2021, in Kingwood, Texas.

       Reginald Mathalone/NurPhoto via Zuma Press via Newscom

       The Railroad Museum on the Strand lines their doors and windows with sand bags to keep flood water out as Tropical Storm Nicholas approaches, Sept. 12th, 2021, in Galveston, Texas.

       Nicholas is slow moving and will likely remain in Texas from Monday to Wednesday.

       ABC News

       Tropical Storm Nicholas is closing in on Texas.

       Rainfall totals will be the highest around Galveston, where over 10 inches are possible.

       ABC News

       Rainfall forecast for Tropical Storm Nicholas.

       Storm surge could be as high as 5 feet south of Galveston.

       Reginald Mathalone/NurPhoto via Shutterstock

       Shop owners line their doors and windows with sand bags and wooden boards to keep flood water out as Tropical Storm Nicholas approaches the island, Sept. 12th, 2021 in Galveston, Texas.

       MORE: ABC News chief meteorologist Ginger Zee explains how hurricanes form

       On Tuesday, Nicholas is forecast to bring heavy rain to eastern Texas and into Louisiana. By Wednesday, some of the heavy rain will begin to reach New Orleans.

       In Louisiana, where residents are still recovering from devastating hurricanes Laura and Ida, Gov. John Bel Edwards has declared a state of emergency.

       MORE: Communities in Louisiana and beyond rally to support Hurricane Ida victims

       During a news conference Monday, Bel Edwards warned residents to take the storm seriously, even though it hasn't reached hurricane status. More than 119,000 are currently without power and 1,425 people are still living in shelters due to Ida, according to the governor.

       "I know that bracing for another storm while we're still responding to and trying to recover from Hurricane Ida is not the position that we wanted to be in, but it is a situation that we are prepared for," he said.

       The rainfall could be as intense as 2 inches per hour, with a total of 5 inches of rain possible.

       "The most severe threat to Louisiana is in the Southwest portion of the state, where recovery from Hurricane Laura and the May flooding is ongoing. In this area heavy rain and flash flooding are possible," the governor said in a statement. "However, it is also likely that all of South Louisiana will see heavy rain this week, including areas recently affected by Hurricane Ida. This tropical storm has the potential to disrupt some power restoration and recovery work currently underway."