The first major storm system expected to strike the United States this hurricane season strengthened into Tropical Storm Barry on Thursday, continuing to dump rain along already inundated parts of the Gulf Coast before its expected landfall on Saturday.
The National Hurricane Center said it could become a Category 1 hurricane by late Friday. The slow-moving storm, which is heading westward to Louisiana at about five miles per hour, was partly to blame for flash flooding in some neighborhoods in New Orleans on Wednesday. Residents who had spent much of the day dealing with floodwaters braced for what was to come: more rain, and a lot of it.
Where is the storm going to hit?
New Orleans is at the eastern edge of the forecast models for the storm’s path, which show that its center could make landfall almost anywhere along the Louisiana coast. The model from the National Hurricane Center also shows the potential for major flooding as far inland as Baton Rouge and southwestern portions of Mississippi.
In the video below, the center’s specialists explain what the forecast “cone” is and its limitations.
“The cone represents the probable track of just the center of the storm,” one of the specialists, John Cangialosi, says. “The center of the storm stays within the cone for roughly two out of every three forecasts.”
The specialists added that hazards associated with a storm usually extend beyond the edge of the cone, and the cone should not be relied on as an indicator of whether to evacuate or not.
Heavy rains may also inundate Mississippi and Texas.
How much rain is going to fall?
About 10 to 20 inches of rain is predicted to fall starting late Thursday night through Sunday night. “The rain is going to be there because it’s a very slow-moving storm,” said Freddie Zeigler, a lead forecaster in the New Orleans/Baton Rouge office of the National Weather Service. “Some of the areas that do not usually flood can flood.” That rain will come after the five to eight inches of rain many New Orleans neighborhoods received on Wednesday.
Will the levees hold?
The Mississippi River, already swollen by spring rains, is expected to crest at New Orleans this weekend at close to 20 feet. The city’s levees along the river are between 20 and 25 feet high, according to Ricky Boyett, the spokesman for the Army Corps of Engineers in the New Orleans District.
The Mississippi River is currently at 16.2 feet, Mike Efferson of the National Weather Service said on Thursday night.
“We’ll be getting to the top of some of our lower levees if the forecast holds,” he said, cautioning that it was still too early to lock in a prediction.
Mr. Boyett said the Corps was trying to identify any low areas and reinforce them. “We’re not concerned with integrity” of the levees, he said, only with how high the water rises.
The city’s pump system is capable of drawing off one inch of water in the first hour after rainfall, but it falls to half an inch per hour after that, according to the Sewerage and Water Board. Though the 10 to 20 inches of expected rain will be spread out over days, there may be times when the rainfall exceeds the pumps’ limits.
But what about the winds? Or storm surge?
The wind picked up to tropical storm speeds of at least 39 m.ph. on Thursday morning. The storm could become a hurricane by late Friday, meaning its winds would have reached at least 74 m.p.h.
Water is far deadlier than winds during a hurricane, experts said. Louisiana is extremely vulnerable to surge flooding because of its coastal and low-lying geography.
National Hurricane Center forecasters also predicted storm surges of three to six feet along the coastal areas. By comparison, the storm surge from Hurricane Katrina in 2005 was at least 25 feet along the Gulf Coast.
Mr. Zeigler said that the Weather Service and the National Hurricane Center in Miami were updating their forecast every couple of hours, and urged residents in Louisiana, Mississippi and Texas to keep checking, as the storm’s path may change.
When does hurricane season begin?
This year’s Atlantic hurricane season officially runs from June 1 to Nov. 30. It’s unusual to have such a sizable storm system this early in the season, records show. Hurricanes have struck Louisiana in July only three times in 168 years. All three were in the last 40 years.
Experts say that trend can be attributed in part to climate change warming the waters of the Gulf of Mexico. A study of recent hurricanes found that climate change had increased rainfall by up to 9 percent.
New Orleans has always endured heavy rains, but the recent inundations and the expectations for this storm are consistent with climate change’s effects: Warmer air holds more moisture, which then comes down as extremely heavy rainfall.
What about evacuation orders?
In Plaquemines Parish, down the Mississippi River from New Orleans and the state’s southernmost parish, nearly 10,000 residents are under a mandatory evacuation order. The areas include the entire east bank of the parish, which sits on the Gulf of Mexico, as well as part of its western bank.
Residents will gather at designated spaces and be taken by bus to a registration point and then travel by another bus to a shelter. Other communities in low-lying areas also called for evacuations on Thursday.
But in New Orleans, Mayor LaToya Cantrell repeatedly requested that residents shelter in place at home, relying on the Army Corps of Engineers’s belief that the levees would hold back most of the water. If water does spill over the levee tops, it would cause only localized flooding. Ms. Cantrell added that the city’s water pumps were working “at optimal capacity.”