Tropical Storm Marco turnedinto a hurricane Sunday while Tropical Storm Laura is expected to follow a similar fate, with storm surges, heavy rainfall and winds predicted to hit the Gulf Coast by Monday, the National Hurricane Center (NHC) confirmed.
A hurricane occurs when a storm's maximum sustained winds reach 74 mph (miles per hour). The Saffir-Simpson Hurricane Wind Scale is a one to five rating based on a hurricane's maximum sustained winds. The higher the rating, the greater the hurricane's potential for property damage, the National Oceanic and Atmospheric Administration (NOAA) explains.
Hurricane and storm surge watches have been issued for most of southern Louisiana, including New Orleans, and southeast Texas, the National Weather Service (NWS) confirmed earlier.
Marco, classified a category 1 hurricane, carries maximum sustained winds of 75 mph, according to the National Hurricane Center. The storm continued its forecasted trajectory toward the southeastern U.S. border on Sunday afternoon, with wind speeds reaching the projected maximum.
The NWS placed Tropical Storm Laura's wind speed at 21 mph on Sunday afternoon, well below its estimated maximum sustained speed of 50 mph. Tropical Storm warnings remained in effect for coastal areas in the Dominican Republic and Haiti.
Laura continued to cause flash flooding over sections of both countries as it tracked about 55 miles south of Cuba, where tropical storm warnings were effected across more than a dozen provinces. Additional warnings related to Tropical Storm Laura were implemented in the central Bahamas, Florida Bay and areas of the Florida Keys.
Hurricane Marco is expected to approach the Louisiana coast on Monday, the National Hurricane Center said in its Sunday advisory. Its morning update warned of "life-threatening" storm surges and heavy rain along areas of the Gulf Coast when Marco makes landfall. A storm surge describes the degree to which coastal waters rise above usual sea levels, and occurs when a storm alters atmospheric pressure and amplifies wind upon arrival.
Meanwhile, Tropical Storm Laura is forecast to strengthen over the Gulf of Mexico, which may bring storm surges, heavy rainfall and winds to portions of the U.S. Gulf Coast by the middle of next week.
"This could result in a prolonged period of hazardous weather for areas that may also be affected by Marco," the NHC noted.
A Hurricane Watch is in effect for the "intracoastal city Louisiana to the Mississippi/Alabama border, Lake Pontchartrain, Lake Maurepas, and Metropolitan New Orleans," the NWS said.
A Storm Surge Watch is in effect for the area stretching from the Sabine Pass to the Alabama/Florida border, Lake Pontchartrain, Lake Maurepas, Lake Borgne, and Mobile Bay. A Tropical Storm Watch has been issued for the area running from the Mississippi/Alabama border to the Alabama/Florida border, the NWS confirmed.
If the peak surge occurs at the time of high tide, the water level could reach a height of four to six feet in the area from the Louisiana town of Grand Isle to the Alabama/Florida border including Lake Borgne and Mobile Bay, and two to four feet in Lake Pontchartrain, Lake Maurepas as well as the area stretching from the Sabine Pass to Grand Isle, the NWS warned.
"The deepest water will occur along the immediate coast in areas of onshore winds, where the surge will be accompanied by large and destructive waves. Surge-related flooding depends on the relative timing of the surge and the tidal cycle, and can vary greatly over short distances," the NWS added.
Mostly minor coastal flooding will be possible in southeast Louisiana, mainly for areas west of the Mississippi River, while gusty winds could blow around loose objects and result in isolated power outages, the NWS noted.
On Friday, Louisiana Gov. John Bel Edwards declared a state of emergency across the state and requested a federal emergency declaration from the White House, with both storms "forecast to impact Louisiana in quick sequence," the governor's office noted in a statement.
Updated and corrected 3:32 PM ET: to correct a previous headline that stated Tropical Storm Laura was upgraded to a hurricane. It has not as of Sunday afternoon.
Updated at 4:35 p.m. ET: to reflect the National Hurricane Center's latest forecast and advisory.
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Soo Kim is a Newsweek reporter based in London, U.K. She covers various lifestyle stories, specializing in travel and health.
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