Tropical Storm Nicholas strengthened to a hurricane in the western Gulf of Mexico Monday night before making landfall along the middle Texas coast during the predawn hours Tuesday.

The storm produced wind gusts over 90 mph and cut power to over 500,000 customers as it bombarded coastal Texas, but forecasters most feared its heavy rain both in Lonestar State and southern Louisiana.

From just south of Galveston to Lake Charles, La., some areas could see rainfall amounts topping 10 inches triggering significant flooding.

Houston, the fourth-largest city in the nation and particularly vulnerable to flooding, could see several inches of rain, but projections for the city were scaled back some on Monday as the storm appeared to be taking more of a coastal rather than inland track.

As the storm gained strength Monday, Texas Gov. Greg Abbott (R) issued an anticipatory disaster declaration for 17 counties.

“Texans throughout the Gulf Coast should prepare now for the impact of Tropical Storm Nicholas, which is expected to bring severe rain and flooding to these communities,” Abbott said in a news release.

Louisiana Gov. John Bel Edwards (D) requested a federal disaster declaration Monday afternoon, which President Biden approved Monday night, ordering federal assistance to supplement state and local emergency response efforts.

On account of the ominous forecast, the Harry Styles concert slated for Monday evening in Houston was canceled.

The National Weather Service declared a rare Level 4 out of 4 “high risk” of flash flooding along the middle and upper Texas coastline where rainfall rates were forecast to reach three inches per hour through early Tuesday.

“Life-threatening flash flooding impacts, especially in highly urbanized metropolitan areas, are possible across portions of the upper Texas Gulf Coast and far southwestern Louisiana,” the Hurricane Center warned.

Nicholas could also bring a “life-threatening” storm surge of several feet to the Texas coastline, spurring shoreside inundation, the Hurricane Center cautioned.

The northern two-thirds of the Texas coast is under a tropical storm warning, with a hurricane warning embedded in the narrow zone of the middle Texas coast from Port O’Connor to Freeport. A storm surge warning covers the zone just north of Corpus Christi through Galveston to the border with Louisiana.

Late Tuesday through Wednesday, Nicholas is predicted to slow or stall over southwest Louisiana, generating heavy rain and potential flooding over some of the same areas of southeast Louisiana ravaged by Hurricane Ida.

Nicholas is one of three tropical systems being monitored in the Atlantic. The other two don’t have name, but may work toward earning them shortly. We’re currently at the peak of hurricane season, and the jam-packed Atlantic isn’t showing signs of quieting.

Nicholas right now

At 2 a.m. Eastern time on Tuesday, Nicholas was about midway between Matagorda and Freeport, Tex., and was heading north-northeast at 10 mph. Maximum sustained winds had increased to 75 mph, from 60 mph earlier Monday, making it a hurricane. It had made landfall around 1:30 a.m. about 10 miles west-southwest of Sargent Beach, Tex.

Radar showed heavy rain along the middle and upper Texas coast into southwest Louisiana from roughly Freeport to Lake Charles. The heaviest rain, so far, had remained southeast of Houston. Around Houston, about 1.5 inches of rain had fallen downtown, with amounts increasing to over 2 inches in Galveston County.

The area from Galveston to just south of Freeport, Tex., was under a flash flood warning where radar indicated at least 3 to 7 inches had fallen.

The Weather Service issued a special bulletin Monday evening for the middle Texas coast warning rainfall rates could reach up to 3 inches per hour after 10 p.m. local time. It noted Port O’Connor had recently received 2.13 inches in an hour.

Along the middle and upper Texas coast, the ocean surge had pushed water levels up to 2 to 4 feet above normal.

Winds gusted up to 95 mph in Matagorda Bay just before 10 p.m. local time while Galveston saw gusts over 60 mph after midnight. About 100,000 customers had lost power in Texas.

Heavy rain and flood threat

It’s not terribly often that the Weather Service declares a “high risk” of flash flooding and excessive rainfall. In fact, high-risk days only make up about 4 percent of forecasts, but are associated with 40 percent of all flood fatalities in the United States and represent about 90 percent of total financial loss from flooding.

As Nicholas parallels the middle and upper Texas coast into early Tuesday, a conveyor belt of downpours could end up contributing to double-digit totals near the coast, and isolated amounts up to 18 inches.

Model simulations suggest Houston will see its heaviest rain through Tuesday morning. Totals of several are possible with the storm, but the heaviest rain could cutoff north and west of Houston with the heaviest rain on its south and east side.

Higher than usual tides will also be problematic. That buildup of water in places like Galveston Bay, exacerbated by a couple of feet of storm surge, will impede freshwater drainage.

By Tuesday morning, the heaviest rainfall should be concentrated near and east of Houston, and may extend to the Golden Triangle region along the Texas-Louisiana border. Rain, heavy at times, will spread over much of the southern two-thirds of Louisiana by Tuesday afternoon.

ln southwest Louisiana, a general 4 to 8 inches of rain is expected, where areas of flooding are likely. This includes Lake Charles, hit twice by hurricanes last year.

The risk of flash flooding will also grow in southeast Louisiana, including New Orleans, between Tuesday and Thursday.

Flash flood watches cover the northern two-thirds of the Texas coastline and coastal Louisiana and extend well inland in both states.

Heavy downpours could also extend into southern Mississippi the second half of Tuesday into Wednesday, eventually reaching western Alabama.

Surge and wind risk

Several feet of storm surge is likely along the immediate coastline, especially if Nicholas manages low-end hurricane strength as it makes landfall. Onshore flow will pile water against the coastline, bringing as much as 2 to 4 feet of extra inundation from Intracoastal City, La., to the mouth of the Rio Grande along the U.S.-Texas border. Not every place will realize a surge, but any places that do could see coastal flooding.

A more significant surge of 3 to 5 feet is possible closer to the storm’s center from Port O’Connor to San Luis Pass, Tex. That includes Matagorda Bay.

Winds overall should be modest when compared against those of some recent Gulf hurricanes like Ida. That said, most areas along the Texas and Louisiana coastline should see winds gusting between 30 and 45 mph, with 60 to 80 mph gusts or greater near the eyewall along the middle Texas Coast in the immediate vicinity of landfall.

Isolated tornadoes are also possible in feeder bands east of the center.

Elsewhere in the Atlantic

Nicholas isn’t alone in the Atlantic. One fledgling storm north of Hispaniola could acquire tropical or subtropical characteristics in the coming days and strengthen, but will remain off the Eastern Seaboard and pass harmlessly west of Bermuda.

Another system, which merits close watching, recently exited the coast of Africa near Senegal and Sierra Leone. Gradual development of the system is likely as it begins its slow trek across the Atlantic. The Hurricane Center gives an 80 percent chance of it becoming a tropical depression or storm over the next five days.

The next two names on the Hurricane Center’s list of storms are Odette and Peter.