Tropical storm Arthur, first of season, threatens east coast hurricane winds

The first storm of the 2014 Atlantic tropical storm and hurricane season formed today. Tropical storm Arthur is currently sitting off the U.S. east coast with maximum sustained winds of 50 mph. Arthur is currently forecast to become a hurricane later this week.

Update 22:00 GMT Wed July 2nd: Tropical storm Arthur now carries sustained winds of 70mph and is not far from hurricane status. The storm is still expected to reach hurricane category 1 before reaching its closest point to the North Carolina coast.

The potential for losses from storm Arthur now lies in how rapidly it can intensify and how close its track takes the center of the storm to the U.S. coastline. Arthur will likely be a category one hurricane at least before it brushes the barrier islands. Currently the models show Arthur as a strong category 1 hurricane with sustained winds of 85mph when it comes closest to North Carolina.

Storm surge is forecast to be between 3 and 5 feet above ground level when Arthur comes closest to the U.S. coastline, which while not severe could cause some flooding to low lying barrier islands.

Update 07.00am GMT Wed July 2nd: Tropical storm Arthur has intensified further into a storm with 60mph sustained winds. Arthur is still expected to become a hurricane by Thursday.

Original story: Tropical storm Arthur formed off the east coast of Florida earlier today. An area of low pressure was initially named a depression and then upgraded to tropical storm status and named Arthur after a Bahamas wind measurement station recorded 39 miles per hour sustained winds.

Arthur has since increased in strength and is becoming better defined, with some analysis suggesting that the early stages of an eye wall are developing on the storms northern wall. Tropical storm Arthur is currently expected to rake the U.S. east coast, strengthening as it goes, with all forecasts pointing towards a category 1 hurricane by Friday.

The forecast path, which you can see below, suggests Arthur will strike North Carolina on Friday as  category 1 storm. With the U.S. 4th July holiday weekend ahead, those areas of Carolina are populated with tourists which will make any evacuation more difficult should it be required.

Tropical storm Arthur forecast path and track - From the NOAA

Tropical storm Arthur has been analysed by risk modeller AIR Worldwide, who said:

The system could develop into a weak Category 1 hurricane later this week, with winds of approximately 75 mph. A mid-latitude low pressure system moving in from the west pushed the storm from a stationary position to the northwest. The storm could pass very close to or possibly make landfall along the Outer Banks of North Carolina early morning on Friday. From there, the storm is forecast to continue moving northeast up the Eastern Seaboard and away from the region this weekend.

“Given the sensitivity of the track to the timing of the mid-latitude low pressure, there is still significant uncertainty in both the track and intensity forecasts at this time,” said Dr. Tim Doggett, assistant vice president and senior principal scientist at AIR Worldwide. “Small deviations in position and intensity over the next 24 hours could have notable impacts on the forecast for later in the week, and thus should be watched carefully.”

According to AIR, if the storm makes landfall in or bypasses North Carolina as a Category 1 hurricane, wind damage to most homes and businesses is not expected to be significant. There may be isolated instances of nonstructural damage to roof coverings and wall cladding, and windows if debris becomes airborne, as well as damage to trees, utility poles, and signage.

A tropical storm watch is in effect from Fort Pierce north to just south of Flagler Beach on the east coast of Florida. This system is expected to bring bands of rain and strong wind gusts, along with the threat of elevated surf, rip currents, and minor coastal flooding as it tracks up the Eastern Seaboard from Florida to North Carolina and farther north this Fourth of July holiday week. Heavy rains of two to four inches will likely affect the Northwest Bahamas and eastern coast of Florida Tuesday through Wednesday, with isolated pockets receiving up to six inches.

Also providing alerts on tropical storm Arthur is insurance and reinsurance broker Aon’s Impact Forecasting unit, who said:

After remaining nearly stationary earlier this morning, Arthur appears to be drifting northwestward. There is no significant change to the previous forecast track as the latest forecast computer model guidance has continued the trend of a pronounced mid-level frontal boundary digging southeastward from the Upper Midwest into the U.S. Northeast and Mid-Atlantic regions within 72 hours. As a result, a steady increase in southwesterly steering flow over the southeastern United States is expected to gradually turn Arthur northward during the next 24 to 36 hours, and then accelerate the system faster toward the northeast on Thursday and Friday. By Days 4 and 5, Arthur is forecast to move over the far north Atlantic as an extratropical cyclone. The NHC track forecast is just an update of the previous advisory, and lies down the middle of the tightly packed guidance envelope.

Northwesterly vertical wind shear is forecast by the forecast models to gradually subside during the next 48 hours, which should allow the cyclone to develop its own upper-level outflow pattern. In fact, the latest visible and water vapor imagery indicates that cirrus outflow has been expanding on the north side of the system during the past few hours, suggesting that the shear conditions could already be subsiding. The low shear conditions and warm sea surface temperatures should allow for at least steady strengthening, and the cyclone is expected to become a hurricane within 72 hours.

It’s worth noting that the latest forecast from the NOAA, which has just been released, says that tropical storm Arthur is expected to become hurricane Arthur as early as Thursday. That would give Arthur plenty of time to strengthen further before its closest pass to the outer banks of North Carolina.

If the storm does strengthen, the storm surge Arthur brings with it will be much larger. At this stage, storm surge looks like being the biggest threat to cause insured losses and with a heavily touristed coastline due to the holidays any worsening in the storm surge expectation for this storm could result in greater damages.

With wind shear expected to lessen, according to Impact Forecasting, Arthur has every chance of feeding off the warm Atlantic waters near the U.S. coastline and intensifying further.

It’s early in the year for an intense hurricane though, so the NOAA’s forecast of a Category 1 hurricane coming close to or hitting North Carolina seems the most likely scenario at this stage. Storm surge will be the biggest threat if that is the case.

We will update you should the forecast begin to look any worse for tropical storm Arthur, or if the track brings Arthur more directly ashore, or if the storm becomes the seasons first Atlantic hurricane. You can keep up to date by visiting our 2014 Atlantic hurricane season page.