No Rest for Grand Bahama Island: Prolonged Storm Surge Threat Ahead for Southeast U.S.

September 2, 2019, 5:03 PM EDT

Above: Infrared satellite image of Hurricane Dorian at 4:30 pm EDT September 2, 2019.

After thrashing Great Abaco Island on Saturday, Dorian parked itself on Monday over Grand Bahama Island, which has been getting the most fierce and prolonged battering from an extreme Atlantic hurricane in history. According to the NOAA historical hurricane database, the only comparable Category 5 beating is the one administered to Honduras by Hurricane Mitch of 1998, which spent 12 hours within 50 miles of the island of Guanaja as a Category 5 storm. However, Mitch's eye did not stay parked over land like Dorian's has.

The unfathomably long stay by Dorian on Grand Bahama continued Monday night. At 11 pm EDT, Dorian was centered about 30 miles east-northeast of Freeport, still holding stationary after moving at just 1 mph for close to 12 hours earlier in the day. The hurricane’s eyewall has been slamming the island for more than 24 hours, and storm surge has been extreme and prolonged over many areas. Sustained winds were 130 mph at 11 pm, making Dorian a low-end Category 3 storm.

There were only scattered reports filtering in Monday from Great Abaco Island, where Dorian ripped ashore on Sunday at peak strength with 185-mph Category 5 winds. Bahamas Prime Minister Hubert Minnis said on Monday that 5 in the Abaco Islands were confirmed dead from the storm. Minnis said there were also numerous injuries, and that the injured had been taken to a hospital on New Providence island.

Storm surge: the biggest U.S. threat from Dorian

After days of uncertainty on crucial aspects of Dorian’s track, computer models came into sharper agreement on Sunday night and Monday. The 0Z ensemble model runs from the European and GFS models closely agreed that Dorian will arc northeastward just off the coast from east central Florida on Tuesday to south of North Carolina by Friday. A small minority (about 10%) of ensemble tracks produce brief, grazing landfalls.

The latest 12Z Monday runs of the four track models that performed best in the two-day time range in 2018—the European, UKMET, HWRF, and GFS—have all fallen in line with a track about 50 - 80 miles from the coast of Florida and Georgia, then growing very close to the coast or making landfall in the Carolinas. Hurricane watches are not issued until 48 hours before a landfall threat, so we can expect such watches to be extended up the Southeast coast over the next day or two as the threat unfolds. As of 11 pm EDT Monday, a hurricane warning was in place from Jupiter Inlet to Ponte Vedra Beach, Florida. Hurricane watches extended south to Deerfield Beach and northeastward all the way to the South Santee River, including most of the South Carolina coast and all of the Georgia coast.

Remember that the average error in a 24-hour NHC forecast is about 40 miles, and a 48-hour forecast is typically in error by about 65 miles.

Comparing Dorian and Matthew

The consensus track for Dorian bears a close resemblance to that of 2016’s Hurricane Matthew, which caused more than $10 billion in U.S. damage as it curled very near the coast from Florida to North Carolina on a coast-hugging track. The latest NHC forecast has Dorian following Matthew's track within about 20 miles, all the way from central Florida to South Carolina. What are the similarities and differences?

Size: Dorian is about the same size as Matthew. During its track up the Southeast U.S. coast, Matthew had hurricane-force winds that extended out about 45 miles to the northwest of the center, and tropical storm-force winds that extended out about 120 miles. For Wednesday, NHC is predicting that Dorian's hurricane-force and tropical storm-force winds will extend out 40 and 120 miles to the northwest, respectively. Hurricane wind fields tend to expand over time and with latitude, especially following eyewall replacement cycles (ERCs) such as the one Dorian completed on Monday.

Speed: Dorian will be a slower mover than Matthew near Florida, but will be accelerating to roughly Matthew's speed as it reaches the Carolinas. Matthew took a day and a half to get from just east of Florida's Space Coast to just south of Wilmington, North Carolina. Dorian is predicted to take about two days to cover the same territory. As a result, water will pile up along the Southeast coast ahead of Dorian for a longer period than with Matthew, and peak flooding may extend over multiple tidal cycles.

Strength: Dorian will probably be about as strong as Matthew, perhaps a little stronger. Dorian will likely be at Category 3 strength as it moves near northern Florida, and it will likely be a Category 1 or 2 off North Carolina. This is quite similar to the weakening that Matthew experienced, although Matthew was already a minimal Category 1 by the time it reached northern South Carolina.

Track: It was uncertain on Monday night exactly where Dorian may track closer to or farther from the coast than Matthew. Matthew made landfall just north of Charleston, South Carolina as a Category 1 hurricane. If Dorian makes any coast-grazing landfalls, the most likely place is North Carolina, according to the 11 pm EDT NHC forecast.

Matthew damage

Figure 1. Highway A1A in Flagler Beach, Florida on Saturday, October 8, 2016, after Hurricane Matthew’s record storm surge chewed up the road. Matthew brought a record storm surge of just over three feet to the Flagler Beach area on October 7, 2016. Image credit: Joe Raedle/Getty Images.

During Mathew, three tide gauges with long-term historical records set all-time records for their highest water level (also called the storm tide, or the water level measured relative to high tide, MHHW): 

Fort Pulaski, Georgia: 4.94’
Previous record: 3.40’ during the October 15, 1947 hurricane (records since 1935.)

Wilmington, NC: 3.48’ 
Previous record 3.47’, during Hurricane Hazel on October 15, 1954 (records since 1935.) 

Mayport, FL: 3.22’
Previous record: 2.47’, during Hurricane Jeanne on September 27, 2004 (records since 1928.)

Top-five high water levels were observed at three other stations:

At Charleston SC: fourth highest on record: 3.51’. The record: 6.76’ during Hurricane Hugo on September 21, 1989; second highest, 4.47’ during the August 11, 1940 hurricane (records since 1921.)

At Fernandina Beach, FL: second highest on record: 4.13’. The record: 6.91’ during the October 2, 1898 hurricane (records since 1897.)

At Springmaid Pier, SC: second highest on record: 6.13’. The record: 8.77’, during Hurricane Hugo on September 21, 1989 (records since 1957.)

All told, Dorian will have the potential to produce some of the largest storm surges on record along the Southeast coast, and will likely be a multi-billion dollar storm due to storm surge damages alone. Whether or not local all-time records occur, as they did during Matthew in 2016 at several locations, will hinge on Dorian’s exact track, timing, and strength.

Dorian is not moving into a strong preexisting frontal zone, so rainfall well inland will not be excessive, at least initially. The most concerning area for potential inland flooding is North Carolina, as by the time Dorian reaches this location (Thursday night into Friday) it may be producing an expansive shield of rains to its north and northeast. Widespread rains of 6-10” and localized amounts well over 10” may be possible over and near coastal North Carolina, which was devastated by massive inland flooding during Matthew as well as during Florence (2018) and Floyd (1999).

Dr. Jeff Masters co-wrote this post.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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Bob Henson

WU meteorologist Bob Henson, co-editor of Category 6, is the author of "Meteorology Today" and "The Thinking Person's Guide to Climate Change." Before joining WU, he was a longtime writer and editor at the University Corporation for Atmospheric Research in Boulder, CO.

bob.henson@weather.com

@bhensonweather

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