Sally could quickly escalate into a Category 2 or stronger storm before landing, with “an extremely dangerous and life-threatening storm surge” forecast, according to the National Hurricane Center. The surge is the storm-caused rise of the water above the normally dry land on the coast.
Double-digit total rainfall is also expected, with the risk of severe widespread flash flooding adding to a growing threat of damaging winds.
A hurricane warning is in effect from Grand Isle, La., Northeast to Ocean Springs, Miss., Including the New Orleans metropolitan area, Lake Pontchartrain, and Lake Maurepas. The region from Morgan City to Grand Isle in Louisiana is under observation for hurricanes. Storm warnings have also been reported between Port Fourchon and the state line between Mississippi and Alabama.
Tropical storm warnings extend into the Florida Panhandle, where heavy rain and flooding are expected.
Sally is a particularly dangerous threat because she is expected to slow and grow stronger as she gets closer to land, potentially prolonging her surge over several tidal cycles and the period of excessive rainfall. Strong winds will also be extended.
The mouth of the Mississippi River could see a seven- to 1
A mandatory evacuation order has been issued outside the area defended by the storm protection system in New Orleans.
Sally is the eighteenth named storm of the 2020 Atlantic hurricane season, the first ever recorded “ S ” named storm and marks one of the last four named systems before running out of hurricane names and returning to the Greek alphabet.
There are tropical problems in other parts of the Atlantic as well, with Paulette heading for Bermuda on the strength of the hurricane and many more tropical waves set to develop off Africa in the coming days.
Sally was a strengthening tropical storm at 11am Sunday, located approximately 280 miles east-southeast of the mouth of the Mississippi River, with maximum sustained winds of 60 mph. It was moving west to northwest at 12 mph. A slowdown in the forward speed is expected for Sunday afternoon until landing from Monday evening to Tuesday morning.
Sally drenched southern Florida, including the Florida Keys and Strait on Saturday, with exceptional rainfall where swaths of rain lingered for hours. Key West International Airport reported a total of 9.37 inches for the date, 3.95 inches of which fell in a single hour between about 9pm. and at 10pm This is the third wettest day ever recorded in Key West history, with records dating back to the 1940s. It was the island’s heaviest rain event since Hurricane Katrina in 2005.
Gusts of wind also accompanied Sally’s passage through South Florida, inclusive a gust to 53 mph on top of a building in Virginia Key.
A morning aerial reconnaissance mission over Sally found the system somewhat lopsided, its winds strongest north of center while most of the storm activity was south. The center of the system is overtaking most of its storm activity due to disruptive wind shear or a change in wind speed and / or direction with altitude. Until that cut relaxes, which should be on Sunday afternoon or evening, Sally will only gradually strengthen.
“All models respond to these changing conditions by showing intensification, but they disagree on the rate of change,” the National Hurricane Center wrote Sunday morning.
There is a possibility that if Sally can become more symmetrical and a solid inner core develops, her rate of strength increase will be more dramatic and rapid escalation will be a possibility.
“Stronger solutions … cannot be ignored,” the agency wrote.
Her current prediction is that Sally will land late Tuesday as a 90 to 100 mph Category 1 or 2 storm, but there is a low-end possibility that the storm – which, barring unforeseen factors, will strengthen to the point of landing – could be even stronger.
Risk of wind and overvoltages
In the area where Sally moves ashore, which the National Hurricane Center predicts will be near or just west of the mouth of the Mississippi River, a corridor of strong gusts of wind reaching 100 mph locally is possible. This will be especially true east of center under Sally’s eyes. Even stronger winds cannot be ruled out along the immediate beaches. Such winds would cause damage to structures, toppling trees and widespread power outages.
Predictions suggest that some gusts between 75 and 90 mph are possible in the greater New Orleans area, but the exact magnitude, direction and location of those winds are highly dependent on course and subject to change.
East of the center, southerly winds will help accumulate water against the coast and generate a severe and dangerous storm, especially during Tuesday’s high tide. However, high water levels and coastal flooding can occur for an extended period due to the slow motion of the storm.
Surge could accumulate up to seven to 11 feet deep, particularly in eastern Louisiana and near Lake Borgne. This is already an area very susceptible to coastal flooding due to the low elevation of the area above sea level and the gradual slope of the underwater continental shelf. Long-term human-caused climate change is increasing the risks of storm surges, making even relatively weak storms a greater danger than a few decades ago. In addition, subsidence of the soil, or sinking, also contributes to this effect, particularly in coastal Louisiana.
Even as far as Mobile Bay in Alabama, a wave of two or four feet is expected.
“An extremely dangerous and life-threatening storm surge is now expected,” said the Hurricane Center.
“The combination of a dangerous storm surge and tide will cause normally arid areas near the coast to be flooded with rising waters moving inland from the coast,” wrote the National Hurricane Center.
The Hurricane Center urges residents to quickly complete preparations for the storm and follow the advice of local officials. Most hurricane deaths occur from flooding, both coastal and inland.
Significant internal flooding is expected
When Sally comes ashore, her forward motion could slow down to a few miles per hour, allowing excessive amounts of rain to build up.
A six- to 12-inch spread is expected for the Greater New Orleans area, Eastern Acadiana, and Florida parishes. Localized quantities greater than 18 inches cannot be excluded. The heavier quantities will be found near the coast, but data suggests that Sally’s remains could bring heavy, heavy rain four to six inches across most of central and southern Mississippi.
With staggering rainfall rates sometimes exceeding three inches per hour, flood clocks are in effect for much of the area. There may be a steep western cut for rainfall if dry air wraps around the system.
Due to the wind shear associated with tropical systems landings, thunderstorms in Sally’s outer rain belts can rotate. This could create an isolated tornado risk, especially east of the center.
The greatest risk to tornado or sea horn activity would be east of downtown, particularly along the Mississippi or Alabama coast or the Florida peninsula Monday through Tuesday.