Barry to unleash severe flooding across Gulf states
Hurricane warnings have been issued, a state of emergency has been declared in Louisiana, the National Guard activated and mandatory evacuations have been ordered in some places along the Louisiana coast as Tropical Storm Barry formed over the Gulf of Mexico on Thursday morning. But in New Orleans, neither mandatory nor voluntary evacuations will be ordered, as the city's mayor advised residents to shelter in place.
Although Tropical Storm Barry is not forecast to become a hurricane before landfall, it will unload feet of rain along the Gulf Coast.
The National Hurricane Center (NHC) declared Barry the second named storm of the Atlantic hurricane season with maximum sustained winds of 50 mph and it was moving west at 3 mph.
Around 4 p.m. CDT, the NHC declared a hurricane warning for portions of the Louisiana coast .
Barry is forecast to make landfall along the Louisiana coast Friday night or Saturday as a potent tropical storm. However, it is not out of the question for it to strengthen into a hurricane just before making landfall.
"The key to whether Barry becomes a hurricane before landfall or not will depend on the amount of time it is able to spend over the warm water of the Gulf of Mexico," AccuWeather Hurricane Expert Dan Kottlowski said.
If Barry turns northward quickly and makes landfall Friday night, then it may not have time to strengthen to a hurricane. If Barry tracks to the northwest for a longer period, it may not make landfall until later Saturday and would have more time to strengthen.
Barry's flooding rainfall to have much more impact than a typical Category 1 hurricane or tropical storm
In terms of impact, AccuWeather is designating this a level 2 storm on its RealImpact™ Scale for Hurricanes. The scale ranges from "Less than 1" to a 5 with 5 having the most severe impact.
"Our greatest concern is for torrential rain that would result in life-threatening flooding," Kottlowski said.
"Heavy, flooding rainfall is expected over a large area, especially over much of eastern Louisiana into parts of southern and central Mississippi and parts of southeastern Arkansas."
Rainfall totals will average 10-18 inches with an AccuWeather Local StormMax™ of 24 inches.
The rainfall amounts assume a steady track. However, should the storm stall over the Deep South, rainfall amounts could be higher. But given that the storm is forecast to potentially be a Category 1 hurricane on the Saffir-Simpson Scale at the time of landfall, officials in New Orleans declined to order mandatory or voluntary evacuations, Mayor Latoya Cantrell told reporters at a news conference on Thursday.
Cantrell said the city only enacts evacuations for hurricanes of Category 3 force or higher. "Therefore, sheltering in place is our strategy," the mayor said.
"This is going to be a significant weather event," Louisiana Governor John Bel Edwards , "and if you haven’t already done so, the time to prepare is NOW. It is critical that you monitor updates and heed the advice of local authorities." Edwards also announced that he'd authorized the Louisiana National Guard to activated up to 3,000 personnel to assist with Barry-related emergencies.
Edwards also implored residents to not attempt to drive on flooded streets and roads. Streets, highways and low-lying areas will be the first to take on water as torrential rain pours down. However, flooding will progress and expand as the storm moves slowly inland.
"To everyone on the Gulf Coast: As you make preparations to protect your homes [and] loved ones from flooding [and] the coming storm, it is imperative that you heed the directions of FEMA, State [and] Local Officials. We are working closely [with] them. Please be prepared, be careful, [and] be SAFE!" President Donald Trump .
Significant rises on the secondary rivers in the region are likely with the risk of major river flooding.
Secondary rivers, such as the Atchafalaya, generally do not contribute to the flow on the Mississippi in the delta region, but rather take water away from the main stem.
However, as heavy rain falls immediately over the lower part of the main stem of the Mississippi, a rise of a few feet can occur on that waterway.
Storm surge severity to depend on track, strength of Barry
How strong the storm becomes and the exact track the storm takes may be critical for both flooding rainfall and storm surge flooding, especially in the city of New Orleans.
Some rise in water is likely along much of the upper Gulf coast, especially along the central and northeastern Gulf coast.
"AccuWeather meteorologists expect a maximum storm surge of 3-6 feet mostly along and just to the right of the storm's path," Kottlowski said.
The greatest storm surge will impact most of the central and southeast coastal areas of Louisiana.
There is concern the levee system may be topped along the Mississippi River due primarily to Gulf of Mexico water backing up the channel. On top of that, heavy rain will pour down on the immediate area from Friday night to Saturday, adding volume to runoff.
Water levels on the lower Mississippi River remain high from spring flooding that was still flowing downstream from the middle and upper part of the basin.
In comparison, the level on the Mississippi River prior to the arrival of Hurricane Katrina was 2 feet. On Thursday morning, the river level was just above 16 feet. Flooding in New Orleans occurred primarily as levees failed as a storm surge caused waters to rise in Lake Pontchartrain.
At New Orleans, the Mississippi River is estimated to surge to near 19 feet, according to National Weather Service (NWS) hydrologists. This was revised downward from 20 feet from original estimates earlier this week.
However, near the 20-foot level, some overtopping of the Mississippi River levee can occur in low spots should this scenario unfold. Levees in New Orleans are between 20 and 25 feet high at different points along the river, according to what Ricky Boyett, the spokesman for the Army Corps of Engineers in the New Orleans District, told The New York Times.
J. David Rogers, the lead author of a definitive 2015 study on the canal wall failures and catastrophic flooding of New Orleans following Hurricane Katrina in 2005 told AccuWeather in an interview that new levees installed in 2011 will provide the city with much better protection from major flooding.
"It’s a much more robust defense system that they have today with probably a 100-fold better site characterization than they had going into Katrina," Rogers said. "You can’t even compare pre-Katrina to post-Katrina; it’s like comparing a biplane to a 747."
The storm will arrive after 6-10 inches of rain deluged New Orleans, which is below sea level, causing a flash flood emergency Wednesday. The drainage system could not keep up with rainfall of 2-3 inches per hour that fell at times, resulting in serious street flooding and numerous high-water rescues.
Damaging winds, tornadoes and waterspouts possible with Barry
While the Barry is forecast to peak no higher than a tropical storm or low-end Category 1 hurricane, sustained hurricane-force winds of 74 mph or greater will only be possible in a small area near and northeast of the eye.
However, with this particular tropical feature being rather larger, bands of severe thunderstorms with wind gusts to tropical storm force can occur well away from the center and especially so on the eastern side of the storm.
There is the ongoing potential for spin-up tornadoes and waterspouts up through a day or two after landfall in the region. Some of these may be wrapped in rain and difficult to see until they are already in the neighborhood.
Some of the oil and gas rigs in the Gulf of Mexico have been evacuated as a precaution, according to CNBC.