(This article, first published Friday morning, was updated at 2 p.m. based on the latest National Hurricane Center advisory.)
After killing at least 22 people in Nicaragua and Costa Rica, Tropical Storm Nate is on a collision course with the northern U.S. Gulf Coast. Southeast Louisiana, including vulnerable New Orleans, lies in the path.
The storm, which is predicted to intensify into a hurricane, should make landfall between late Saturday night or early Sunday morning. Damaging winds and flooding threaten the region from roughly Morgan City, La., to Pensacola, Fla.
Likelihood (percent chance) of tropical storm-force winds. (National Hurricane Center)
Along the coast, near and just to the east of where the storm center moves ashore, a storm surge or rise in ocean water of several feet above normally dry land is expected. “Life-threatening storm surge flooding is likely along portions of the northern Gulf Coast, and a storm surge warning has been issued from Morgan City, Louisiana, to the Alabama/Florida border,” the National Hurricane Center said.
The Hurricane Center has issued hurricane warnings for southeastern Louisiana and coastal Mississippi and Alabama, including Biloxi and Mobile. New Orleans and Pensacola are under a tropical storm warning and hurricane watch, and both are included in the storm surge warning zone. Rainbands and tropical-storm force winds could begin there as soon as Saturday afternoon.
“[P]reparations to protect life and property should be rushed to completion in these areas,” the Hurricane Center said.
While somewhat disorganized, Nate has emerged over the warm waters of the Caribbean where it has begun to strengthen. At 2 p.m. Friday, it packed 50 mph maximum winds and was centered 125 miles east-southeast of Cozumel. The storm is booking to the north-northwest at 21 mph.
By Saturday, after raking over the Yucatán Peninsula, the storm will emerge in the Gulf of Mexico where it could gain more strength before slamming into the U.S. Gulf Coast on Saturday night or early Sunday.
(National Hurricane Center)
While the official National Hurricane Center forecast indicates Nate will be a Category 1 hurricane at its U.S. landfall, the intensity forecast is very challenging. A range of intensities is possible at landfall.
While the storm is passing over very warm water, favorable for intensification, it will also interact with land areas over the Yucatán Peninsula as well as pockets of wind shear and dry air, which could slow the strengthening process. There is a small chance that the storm could be only a weak to moderate tropical storm at landfall along the Gulf Coast. However, because it’s passing over areas of very warm water, there is also the outside chance it becomes a destructive Category 2 or 3 hurricane.
Map of ocean heat content over the western Caribbean and Gulf of Mexico on October 6. (UMiami)
The track forecast is more certain, and the majority of model simulations have converged on landfall between Southeast Louisiana and the Alabama-Florida border. Of course, exactly where in this zone the storm comes ashore is important, as the core of strongest winds is likely to be fairly small and the storm’s most severe hazards will tend to occur near and just to the east of where it makes landfall.
Group of simulations from American (blue) and European (red) computer models for the path of Tropical Storm Nate from early Friday. Each color strand represents a different simulation with slight tweaks to initial conditions. Note that the strands are clustered together where the forecast track is most confident but they diverge where the course of the storm is less certain. The bold red line is the average of all of the European model simulations, while the bold blue line is the average of all the American model simulations. (StormVistaWxModels.com)
New Orleans in focus
Around New Orleans, the main concerns are the storm surge and potential for flooding rain.
If the storm makes landfall just west of the city, it could push a surge of 4 to 7 feet above normally dry land, causing significant inundation. Landfall east of the city would reduce the surge potential some.
In a worst-case surge scenario, the National Weather Service warns that “large areas of deep inundation” could occur, causing “structural damage to buildings, with several washing away.” It also said roads could be washed out with “major damage to marinas, docks, boardwalks and piers.”
Two to four inches or more of rain are forecast in New Orleans, enough to cause localized flooding, the Weather Service said. Because Nate will move through the region relatively quickly, it will limit the potential for more serious rainfall. The Advocate, a news organization serving New Orleans, wrote that several of the city’s pumping stations, which help dislodge floodwaters, are not at full capacity, which could cause problems if rainfall is at the high end of projections.
The broader Gulf Coast and eastern United States
The last time this part of the coastline experienced a hurricane landfall was Category 1 Hurricane Isaac in late August 2012, and Nate should produce similar impacts.
Because the worst weather is expected near and just east of the storm center, areas east of New Orleans, including Biloxi, Mobile and Pensacola, are somewhat more likely to experience serious impacts, including damaging wind gusts, a storm surge of several feet and at least several inches of rain.
After Nate crosses the coast, it is likely to carry a serious swath of heavy rainfall to the north and northeast between Sunday and early next week. The Southern Appalachians, in particular, may face a flash flooding risk Sunday and Monday — as at least 3 to 6 inches of rain could fall in a short time.
National Weather Service rainfall forecast through Thursday. (WeatherBell.com)
Before it gets to the United States, though, it has produced and continues producing tremendous rainfall, which is causing flooding and mudslides in Costa Rica, Nicaragua and Honduras, where — in addition to the 22 fatalities — many people are missing. It will pass over or near Cozumel and Cancun on Friday night, where tropical-storm force winds and heavy rain are likely.