One, Hurricane Florence, is already cause 85-mph winds expected to become an "extremely dangerous" major hurricane.
According to the noon-time update from the NHC, operated by the National Oceanic and Atmospheric Administration (NOAA), Florence now has sustained winds of almost 130 miles per hour and has no become what the agency considers "a major hurricane".
"There is an increasing risk of life-threatening impacts from Florence: storm surge at the coast, freshwater flooding from a prolonged and exceptionally heavy rainfall event inland, and damaging hurricane-force winds", the National Hurricane Center said in an update on Florence's progress at 5 a.m. Monday.
Maps of the storm's trajectory showed it likely to come ashore somewhere near the border of North Carolina and SC.
Gov. Northam declared a State of Emergency for the Commonwealth Saturday, one day after Gov. Roy Cooper declared a State of Emergency for North Carolina. Latest forecasts have Florence making landfall in the vicinity of Wilmington, North Carolina Thursday evening/night.
"We have already began mobilizing our assets to respond accordingly, and we are here for you!" he tweeted.
A high-pressure ridge building to the north and northwest of Florence is expected to steer the hurricane west-north-westward to northwestward toward the southeastern US coast.
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"We know this evacuation order I'm issuing is going to be inconvenient", McMaster said of the decision, which affects over 1m residents. Florence was upgraded twice Monday to a Category 4.
"North Carolina is no stranger to hurricanes", Cooper said Monday, at least partially alluding to the devastating effects of Hurricane Matthew, which struck the Carolinas as a category 1 storm in October 2016 killing 34 in the United States, after cutting a vicious path across the Caribbean, killing more than 1,000 in Haiti. The United States was hit with a series of high-powered hurricanes previous year, including Hurricane Maria, which killed about 3,000 people in Puerto Rico, and Hurricane Harvey, which killed 68 and caused an estimated $1.25 billion in damage from catastrophic flooding in Houston.
By noon EDT on Monday, Florence had top sustained winds of 130 miles per hour (195 kph). SCEMD has also put their preparedness level at OPCON 2, the second-highest level for the state of emergencies in SC. Mandatory evacuations have begun along North Carolina's coast.
Florence, the most intense of the three has reached Category 4 status and will likely continue to strengthen as it moves over the warm waters heading for landfall on the East Coast later this week.
Helene - now just southeast of the Cabo Verde islands off the African coast - had winds of 136km/h, and was expected to turn northwest and then north into the open Atlantic by midweek, the NHC said.
First, here's a map from the National Hurricane Center showing a forecast cone and coastal watches and warnings.
Meanwhile, Hurricane Isaac is expected to weaken as it approaches the Lesser Antilles in the Caribbean, and then possibly fall apart.