September 2, 2019

Hurricane Dorian Remains A Powerful Storm As It Prepares To Curve Up Southeast Coast



Dorian remains a powerful hurricane Monday night as it sits stationary just two-dozen miles north of Grand Bahama. The hurricane's intense winds continue to roar across the Bahamian island after more than a day, an event of unprecedented intensity and duration. The storm will come dangerously close to the southeastern United States over the next three days, potentially bringing hazardous conditions to the entire coast from West Palm Beach, Florida, to Cape Hatteras, North Carolina.

Current Forecast

Hurricane Dorian stalled over Grand Bahama on Sunday night and hasn't moved but a few dozen miles since then, raking the island with hurricane force winds for more than an entire day. The hurricane remained stationary on Monday evening, but it should start to lift northwest on Tuesday and pick up speed through the rest of the week.

The latest forecast from the NHC shows Dorian passing Florida's east coast with maximum sustained winds in excess of 120 MPH. The core of the storm will come close enough to the Florida coast that tropical storm force winds could extend as far inland as Orlando. Hurricane force winds are possible for a time near the coast as the storm passes by. Folks in Florida under watches or warnings should be prepared for downed trees, flooded roads, and the possibility of a few days without power.

Keep in mind that it wouldn't take much of a westward nudge in Dorian's track to bring dangerously high winds and storm surge closer to the coast.

Forecasters expect the hurricane to begin its curve northeast on Wednesday night or Thursday morning, roughly paralleling the southeast coast until it passes the Outer Banks on Friday. Hurricane watches are up from the Florida/Georgia line north through the Charleston area. Expect these watches to be upgraded to tropical storm or hurricane warnings by Tuesday morning, with more watches and warnings following the track of the storm up the coast through Thursday.

Hurricane Dorian will lose its tropical characteristics as speeds northeast through the western Atlantic Ocean by the end of the week. Nova Scotia could see a period of hurricane force winds from this storm as it races through the region next weekend. Folks in Atlantic Canada should closely monitor this storm and start preparing now for the possibility of hurricane force winds, power outages, coastal flooding, and flooding from heavy rain.

Expanding Wind Field

Hurricane Dorian finally experienced an eyewall replacement cycle early Monday morning. Dorian managed to maintain its category five intensity for so long in part because it never underwent an eyewall replacement. It's likely that upwelling of cooler waters and the friction of sitting over land finally destabilized the hurricane's inner structure enough that the storm went through the process of generating a new eyewall.

As I pointed out in last night's update, the process of shedding and generating new eyewalls weakens a storm while causing the storm's overall wind field to expand outward. Tropical storm force winds (38+ MPH) extend 150 miles from the center of the storm, while hurricane force winds (74+ MPH) extend 45 miles from the center of the storm.

Impacts


Every state between Florida and Virginia has declared a state of emergency for areas expecting to deal with hazardous conditions this week. These emergency declarations sound ominous, but it's just an order that activates different parts of state and local government to respond to a storm. A state of emergency allows officials to do things like order evacuations and call up the National Guard to help with preparedness and response. These orders are also a prerequisite for states to receive emergency funds from federal agencies like FEMA.

Here's what you can expect along and near the southeast coast as Hurricane Dorian starts pulling through the region over the next three days.

WIND: Hurricane force winds are possible along the coast where hurricane warnings are in effect. Winds in excess of 74 MPH could lead to power outages, downed trees, flying debris, and structural damage. Tropical storm force winds are possible even farther inland, which could also lead to downed trees and power lines. The threat for damaging winds will go up if the storm tracks closer to land.

STORM SURGE: A 4-7 foot storm surge is possible at high tide along the coast where hurricane watches and warnings are currently in effect. Wind direction, wind speed, and coast shape will determine surge depths in each individual spot along the coast. Some areas could see no surge, while others could see a life-threatening inundation. The probability of a storm surge increases with stronger onshore winds.

FLOODING: Heavy rains near the coast could lead to flash flooding. The Weather Prediction Center expects 4-8 inches of rain along and near the southeastern coast, with higher amounts where rain bands begin training or if the storm makes landfall. The highest rainfall totals are likely in the eastern Carolinas where the center of the storm could make (or come close to making) landfall.

TORNADOES: The threat for tornadoes is low since the right-front quadrant of the storm is forecast to remain offshore.

Unprecedented Conditions In The Bahamas

An infrared satellite loop of Hurricane Dorian between 8:01 AM EDT September 1, 2019, and 9:01 PM EDT September 2, 2019. | College of DuPage


Folks on Grand Bahama continue to experience what is likely one of the most extreme weather events ever experienced by humans outside of mountaintops or polar shipping lanes. We use "extreme" and "catastrophic" and "worst-ever" so often that it can lose its punch. This is one of those rare instances where you can't exaggerate reality because it's so deeply unprecedented.

Most scale-topping hurricanes keep moving and quickly lose steam once they touch land. This storm didn't do that. Hurricane Dorian found an extremely favorable environment over the northwestern Bahamas for strengthening and maintaining that strength. Calm winds throughout the atmosphere around the storm have allowed the hurricane to sit and spin over the same spot for hours at a time. The terrain of Grand Bahama is low and flat enough that it hasn't had a destructive impact on the storm's internal structure.

This sequence of events left much of Grand Bahama firmly wedged in the eyewall of a category five/category four hurricane for 24+ hours with almost no break except for where the eye passed overhead. There have only been a handful of hurricanes this intense in recorded history, and none of them slowed to a crawl over an island and maintained their intensity for almost an entire day.

This will be a historic storm for many reasons, but not the least of which is the level of destruction we're likely to see on Grand Bahama once rescue crews are able to make their way to Freeport and surrounding areas.


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I graduated from the University of South Alabama in 2014 with a degree in political science and a minor in meteorology. I ran Gawker's The Vane for two years and I've contributed to Mental Floss, Forbes, Popular Science, and the Washington Post's Capital Weather Gang. I also teamed up with Outdoor Life to write a book called The Extreme Weather Survival Manual, which came out in October 2015.

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