Forecast Update: North Carolina on Watch for Hurricane Arthur

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Tropical Storm Arthur is forecast to strengthen into a hurricane within two days and threaten North Carolina’s Outer Banks, where tourists are visiting for the Fourth of July holiday, while also adding to heavy rain in New York.

The storm was 90 miles (145 kilometers) east of Cape Canaveral, Florida, with maximum sustained winds of 60 miles per hour, the Miami-based National Hurricane Center said at 5 a.m. local time today. Hurricane watches were posted for North Carolina’s Bogue and Oregon inlets and Pamlico Sound. Tropical storm watches were in effect for parts of North Carolina, South Carolina, Virginia and Florida.

“Strengthening is forecast during the next 48 hours and Arthur is expected to become a hurricane by Thursday,” the center said in the advisory.

In New York, showers and thunderstorms are expected to develop late today and tomorrow, a combination of the cold front slowly approaching and tropical moisture streaming in from Arthur. New York has a 50 percent chance of rain on July 4, according to Joe Pollina, a weather service meteorologist based in Upton, New York.

“It would mainly be from the cold front,” he said by phone yesterday. “Arthur is going to be somewhere in the southeast or Mid-Atlantic region by then, well to our south.”

Hurricane Scale

Arthur is the first named system of the 2014 Atlantic hurricane season, which runs from June 1 through Nov. 30. Its winds are expected to peak at 85 mph within two days, making it a Category 1 storm on the five-step Saffir-Simpson hurricane scale, the center said.

The system will probably pass over or near Dare County, in easternmost North Carolina, early on July 4. Officials will regroup today, after meeting yesterday to discuss what action to take, because the forecast remains “uncertain,” a notice on the county website shows.

In the Pacific, the hurricane center is also monitoring Tropical Storm Douglas, which is meandering southwest of Baja California. Remnants of the former Tropical Storm Elida are expected to produce rains in western Mexico and dissipate in the next two days.

Mid-Day Update from AIR Worldwide

According to catastrophe modeling firm AIR Worldwide, Tropical Storm Arthur continued to strengthen overnight as it slowly churned its way up the Florida east coast. The National Hurricane Center’s (NHC) forecast as of 11 a.m. EDT showed the storm possibly becoming a hurricane tomorrow and passing very close to or over the Outer Banks of North Carolina on Friday—most likely as a Category 1 hurricane. Precipitation from the storm could reach the Carolinas early Thursday morning.

As of 11 a.m. EDT today Arthur was about 105 miles east-northeast of Cape Canaveral, Florida, with maximum sustained winds of 60 mph and higher gusts. The storm has picked up speed and is now moving north at 7 mph. The NHC has issued a hurricane watch in North Carolina from Bogue Inlet to Oregon Inlet, including Pamlico Sound. A tropical storm warning has been issued for the North Carolina coast.

“Arthur has become a more organized system,” said Dr. Tim Doggett, assistant vice president and senior principal scientist. “Yesterday evening an Air Force reconnaissance aircraft found that Arthur had begun to form a discernable eyewall on the storm’s northern wall. Arthur is now over warm waters in the Gulf and wind shear is low—conditions favorable to storm strengthening. On the other hand, Arthur is encountering some dry air over land that will keep the system from intensifying quickly. However, the majority of models are in agreement with the NHC forecast, predicting that the system will reach hurricane strength by tomorrow, July 3.”

According to AIR, the majority of single-family residential structures along the U.S. east coast are of wood-frame construction. At Category 1 wind speeds, it is possible that these structures could experience minor damage to roof covering and wall cladding. Any debris mobilized by Category 1 winds could cause damage to unprotected windows. In addition, there may also be cases of damage due to downed trees—a possibility exacerbated by soils already saturated from recent heavy rainfall.

Mobile (manufactured) homes and light metal structures are much more vulnerable than structures of other construction types, and these types of structures could experience some structural damage, AIR said. Engineered structures such as reinforced concrete and steel buildings should experience very little damage, although there may be isolated instances of damage to nonstructural elements, such as to windows, cladding, and roof coverings, according to the modeling firm.

AIR said its analysis of damage data over time has indicated that building vulnerability can change significantly due to changes in building codes and code enforcement, changes in material and construction practices, and structural aging. North Carolina has a long history of evolving building codes. The state’s codes since 2002 have been based on the International Building and Residential Code. AIR said it expects newer structures in the region will perform better than older structures.

At present, a trough of low pressure is expected to curve Arthur to the north-northeast, bringing the storm near the coast of South Carolina on Thursday. Arthur will then move parallel to the East Coast, possibly arriving as a Category 1 hurricane on the North Carolina Outer Banks on Thursday. The storm may bring sustained winds exceeding 70 mph, heavy rain, and coastal flooding from storm surge, although these impacts may be relatively brief because of the storm’s relatively quick northward motion. From there, the storm is expected to track up the northeast coastline before transitioning to an extratropical storm.

“Such long-range forecasts have considerable uncertainty, and a slight westward—or eastward—shift in the track today or tomorrow will have implications for any storm impacts in the Northeast,” Doggett said.

According to the NHC, Arthur is expected to produce rainfall accumulations up to 4 inches over coastal areas of North Carolina through Thursday. Storm surge from Arthur may raise water levels by as much as 4 feet along parts of the North Carolina coast.