Hurricane Arthur Pounds North Carolina, Heads for Nova Scotia

Hurricane Arthur has weakened to a Category 1 storm with 90 mph winds on Friday morning, after delivering a direct hit to the barrier islands of eastern North Carolina on Thursday night. Officially, Arthur made landfall at Shackleford Banks between Cape Lookout and Beaufort, North Carolina at 11:15 pm EDT July 3, 2014 as a Category 2 hurricane with 100 mph winds. It was the first Category 2 hurricane to make U.S. landfall since Hurricane Ike of 2008 (which had 110 mph winds at landfall.) Arthur is only the fourth July hurricane to hit North Carolina since accurate records began in 1851, and the earliest in the year to hit the state. Other July hurricanes to hit the state occurred in 1901, 1908, and 1996. Fortunately, no deaths or injuries were reported due to Arthur, and damage was minimal, said North Carolina governor Pat McCory at a 9:30 am EDT July 4 press conference, though 44,000 customers lost power. The vast majority of the 60,000 permanent residents who live on the Outer Banks did not evacuate. Highway 12 connecting the Outer Banks to the mainland was flooded and covered with sand, but is scheduled to re-open on Saturday. The Bonner Bridge crossing Oregon Inlet on Highway 12 needs to be inspected before it can re-open, since there is concern that the 4.5' storm surge that roared though the inlet early Friday morning may have scoured sand away from the support pilings. Luckily, the highest surge occurred at low tide.


Figure 1. NASA astronaut Reid Wiseman tweeted this photo of the storm from the International Space Station taken through a 10.5mm fish eye lens at 9:30 am EDT July 4, 2014. At the time, Arthur was a Category 1 hurricane with 90 mph winds.


Figure 2. Radar out of Wilmington, North Carolina at 11:22 pm EDT July 3, 2014, as Arthur made landfall at Cape Lookout, NC.


Figure 3. Total radar-estimated rainfall for North Carolina from Arthur from the Wilmington, North Carolina radar.

Wind, wave, storm surge, and tornado reports

Here are the top winds measured in North Carolina from Arthur:

Cape Lookout CMAN, 71 mph gusting to 84 mph at 10 pm (though NHC reported that this station had sustained winds of 77 mph, gusting to 101 mph between the regular hourly reporting times)
Beaufort, 54 mph gusting to 69 mph at 10:24 pm
Cape Hatteras USCG, 64 mph gusting to 78 mph at 1:36 am
Oregon Inlet Marina, 54 mph gusting to 69 mph at 5:24 am

A significant wave height of 21.3' was observed at Oregon Inlet at 4:47 am EDT.

Here are the top storm surge levels measured at NOAA tide gauges from Arthur:

4.5' at Oregon Inlet, NC
2.5' at Hatteras, NC USCG Station
2.4' at Beaufort, NC
2.1' at Duck, NC
2.1' at Sewells Point, VA
2.1' at Chesapeake Bay Bridge Tunnel, VA

NOAA's Storm Prediction Center recorded one tornado in North Carolina on Thursday from Arthur; the tornado did only minor damage.


Figure 4. Aerial view of Highway 12 to the North Carolina Outer Banks on the morning of July 4, 2014 after the storm surge of Hurricane Arthur had scoured the coast. Image credit: U.S. Coast Guard.

Forecast for Arthur
Satellite loops on Friday afternoon showed that Arthur's eye had filled with clouds, and the storm had expanded in size. Top winds of the hurricane at 11 am EDT were still a formidable 90 mph, with the central pressure a respectable 976 mb. With wind shear a high 25 knots and sea surface temperatures a chilly 24°C, Arthur will steadily weaken, but is still expected to have 70 - 75 mph winds when it makes landfall in Western Nova Scotia between 5 am - 8 am EDT Saturday, July 5. By late morning Saturday, Arthur will complete the transition to a powerful extratropical storm with tropical storm-force winds. The 11 am EDT Friday wind probability forecast from NHC gave Yarmouth, Nova Scotia a 12% chance of hurricane-force winds, and a 93% chance of tropical storm-force winds. Nantucket and Cape Cod, Massachusetts were given 88% and 54% chances of tropical storm-force winds, respectively.

Arthur's formation is not a harbinger of an active hurricane season
The first hurricane of the season typically occurs on August 10, so Arthur is quite a bit ahead of schedule. Arthur was able to form so early because it was over the very warm waters of the Gulf Stream Current, and these waters happened to be over 1°F warmer than usual for this time of year. Formation of a June or July hurricane like Arthur off the U.S. coast is typically not a harbinger of an active hurricane season, since these storms do not form from African tropical waves. Arthur spun up from a cluster of thunderstorms and their associated low pressure system that moved off the Southeast U.S. coast, and hurricanes that get their start this way are typically too far north and too close to land to be able to intensify into major hurricanes. The bigger threat are hurricanes that get their start from tropical waves traversing Main Development Region (MDR) for hurricanes (from the coast of Africa to Central America between 10° - 20°N, including the Caribbean Sea.) Tropical waves that traverse the MDR are responsible for 85% of all major (Category 3 and stronger) hurricanes. When June and July hurricanes and tropical storms form in the MDR, it usually does portend an active hurricane season, since it shows that atmospheric and oceanic conditions are primed to assist development of tropical waves coming off the coast of Africa during the peak mid-August through mid-October part of hurricane season.

A better way to evaluate whether or not this will be an active hurricane season is to look at sea surface temperatures (SSTs) in the MDR, and the status of El Niño. MDR SSTs are currently very close to average, and are thus unlikely to contribute to an above-average hurricane season. The very warm equatorial waters currently off the coast of South America suggest that an El Niño event is in the process of developing. When an El Niño event occurs during hurricane season, it tends to create an atmospheric circulation that brings unusually strong upper-level winds to the tropical Atlantic. These strong winds create a shearing action (wind shear) on any tropical storms or hurricanes that may be attempting to form, disrupting their circulation. Thus, the pre-season predictions of a below-average or near-average hurricane season still look good.


Video 1. ‪Hurricane Arthur at The Frying Pan Tower Adventure B&B‬ (thanks to Skyepony for posting this link in my blog comments.)

Jeff Masters