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(CNN)Tropical Storm Sally could be a Category 2 hurricane when it reaches the United States near New Orleans on Tuesday morning.
Hurricane warnings have now been issued from Morgan City, Louisiana, east to Ocean Springs, Mississippi, including New Orleans, Lake Pontchartrain and Lake Maurepas. Sally continues to strengthen across the Gulf of Mexico with sustained winds of 60 mph.
Storm surges of up to 7 to 11 feet are possible near the center of the storm and just east of where landfall is expected. Along with storm surge, extreme rainfall amounts of over a foot are expected in some locations between southeast Louisiana and the western Florida panhandle.
Tropical Storm Sally is the 18th named storm of the 2020 Atlantic hurricane season, the earliest 18th-named storm on record. On Saturday, the storm brought heavy rain and gusty winds to south Florida as it moved into the Gulf of Mexico.
Louisiana Gov. John Bel Edwards declared a state of emergency Saturday evening ahead of Sally's arrival.
"While we ultimately don't know where Sally will make landfall, much of Southeast Louisiana is in the storm's cone and the risk of tropical storm force or hurricane strength winds continues to increase. This storm has the potential to be very serious," Edwards said in a news release.
In New Orleans, Mayor LaToya Cantrell issued a mandatory evacuation order for residents outside of the city's levee protection system. The evacuation will begin Sunday at 6 p.m. for the areas of Venetian Isles, Irish Bayou and Lake Catherine.
Cantrell said Sunday that sandbags were available throughout the city and that water pumps are in place and operational.
In coastal Louisiana, Grand Isle is under a mandatory evacuation, and a recommended evacuation notice went out to the community of Port Fourchon.
Gulf Coast expecting 6 to 12 inches of rain
Flash flood watches are in effect along the Gulf Coast across much of southern Louisiana, east to the Florida Panhandle, and along the western Florida peninsula. These watches include the city of New Orleans, Biloxi, Mississippi, Mobile, Alabama, and Panama City and Tampa, Florida.
Sally is expected to slow in speed as it approaches the Gulf Coast which will result in significant flash flooding across the region. Widespread rainfall totals of 6 to 12 inches is expected along the Gulf Coast through Wednesday, but isolated rainfall of up to 20 inches is not out of the question.
The combination of extreme rainfall and the high storm surge will bring widespread flooding to much of the Gulf Coast beginning on Monday and lasting at least through Wednesday.
Most forecast models have Sally moving toward the northern Gulf Coast and likely making landfall somewhere between New Orleans and Panama City by late Monday or Tuesday. However, if the track shifts farther west or slows down, landfall may hold off until Wednesday.
"The cyclone will likely become a hurricane in 2 to 3 days, although an increase in vertical shear could slow the rate of intensification over the northern Gulf of Mexico," according to the National Hurricane Center.
Once it reaches that area of the Gulf Coast the steering patterns break down and the system meanders near the coast.
Whether the meandering is offshore prior to a landfall or onshore will not make much of a difference in terms of rainfall. In either case, because of the slow forward movement along the Gulf Coast significant flooding is possible.
Active hurricane season stays busy
Another system, Tropical Depression Twenty, formed in the central tropical Atlantic on Saturday, according to the NHC. Twenty has sustained winds of 35 mph.
Twenty is expected to strengthen to a tropical storm by Sunday evening and a hurricane by Tuesday, and if so, will be named Teddy. The previous record for the earliest 19th named storm is October 4, 2005.
So far this season, there have been 18 named storms. The average for an entire season is 12. Early in the season, forecasters called for a very active season.
Many storms broke records for being the earliest named to date. All but three named storms (Arthur, Bertha and Dolly) set records for being the earliest named storm for their respective letter. After Sally, there are only three names left on this year's official list: Teddy, Vicky, and Wilfred. After that, the NHC will move on to using the Greek alphabet.
Sally is just one of several systems in the Atlantic. The NHC is currently watching seven areas: one hurricane, one tropical storm, two tropical depressions and three tropical disturbances. Thursday marked the peak of the Atlantic hurricane season.
Hurricane Paulette is forecast to track toward Bermuda and potentially make landfall early Monday morning as a category 2 storm. A hurricane warning is in effect for Bermuda and hurricane conditions are expected tonight.
On Thursday, the National Oceanic and Atmospheric Administration announced they are issuing a La Niña Advisory, meaning La Niña conditions are present in the central and eastern Pacific Ocean.
In a typical El Niño phase, much of the Pacific Ocean is characterized by warmer waters, whereas La Niña features a cooling of those same Pacific waters. In the case of hurricanes, La Niña weakens high atmospheric winds, which allows warm air pockets to grow vertically and develop into hurricanes.
