Tropical storm Arthur nears hurricane intensity: a guide to coastal impacts around July 4 holiday

Just flew over TS #Arthur – hoping it heads to sea. Looks mean. pic.twitter.com/9IjqFFy35m — Reid Wiseman (@astro_reid) July 2, 2014

Tropical Storm Arthur is not producing any surprises, so far.  It has intensified to a moderate tropical storm, the turn to the north has begun this morning, and it is still forecast to become a hurricane as it brushes by the Outer Banks on Independence Day.

A tropical storm warning is now out for the North Carolina coast (and a hurricane watch for parts of the Outer Banks), with strong winds and flooding likely for the Carolinas Thursday into Friday.

Further north, Friday looks like a bad day at the beach on the Maryland and Delaware shore, but followed by a beautiful Saturday and Sunday. Of note, the track forecast for Arthur is more certain than we often see with tropical systems.

 

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Track forecast from National Hurricane Center and active watches and warnings (click to enlarge)

Track forecast from National Hurricane Center and active watches and warnings (click to enlarge)

System type: Tropical Storm
Intensity: 60 mph, 997 mb (updated 11 a.m. EDT)
Location: 105 miles east of Cape Canaveral, Fla.
Intensification potential: High (confidence: high)
Landfall potential: Medium (confidence: medium)
Days from possible landfall: 1.5-2
Zones to watch for possible landfall: North Carolina (confidence: high)
Will if affect VA/MD/DE beaches? Yes, during day on Friday (confidence: medium)
Will it affect D.C.? Not directly, but cold front with enhanced t-storms possible Thursday (confidence: medium)

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Forecast for the Eastern Seaboard

The track forecasts remain unchanged over the past day.  The northward motion will accelerate today, followed by a gradual turn to the northeast tomorrow.  It is still expected to pass east of South Carolina tomorrow as a minimal hurricane, then graze the Outer Banks of North Carolina as a hurricane Thursday night into Friday morning.  Then it heads offshore by a safer distance, passing east of the mid-Atlantic region during the day on Friday and east of New England on Friday evening/night, perhaps still as a hurricane.

I have outlined some  coastal hotspots and their peak impact timelines below (clicking on the names will take you to the latest NWS forecast and conditions for that location):

Charleston, SC - Thursday daytime… gusty winds, intermittent heavy rain and thunderstorms, minor storm surge flooding (2-4′) along coast/rivers/inlets, beach erosion and rip currents.  Friday night… should be beautiful for fireworks!

Wilmington, NC - Thursday afternoon into Thursday night… windy with gusts to tropical storm force, rain and thunderstorms expected, moderate storm surge flooding expected (3-5′), especially along coast, but also up into rivers and inlets, beach erosion and rip currents.  Back to normal in time for the holiday and fireworks!

Outer Banks, NC - Thursday afternoon through Friday morning… rain and wind increasing, reaching peak on Thursday night, possible hurricane force winds.  Very rough sea with coastal flooding and beach erosion. Evacuations have not been ordered but officials are keeping close watch on the storm and they are not out of the question.   Friday evening should be fine for fireworks although some have been rescheduled for Saturday, Sunday or Monday

Ocean City, MD - Thursday night into Friday night… worst conditions will be Friday daytime with rain and thunderstorms possible, breezy with gusts 30-35 mph, bad day for the beach on Friday.  Fireworks outlook is iffy – MIGHT clear out by nighttime, but still breezy. Saturday and Sunday look great.

New York City, NY - Little impact from Arthur, but some heavy rain and thunderstorms associated with cold front from Wed evening through Fri morning. Coastal areas like Long Island can expect minor storm surge and beach erosion.  Friday evening should be great for fireworks!

Cape Cod, MA - Thursday daytime through Saturday morning… worst conditions will be on Friday night.  Scattered rain and thunderstorms start Thursday afternoon, increasing through Friday evening.  Winds 30-35mph on Friday night into Saturday morning.  Storm surge flooding possible, along with rip tides and beach erosion.  Outlook for fireworks on Friday is very poor… wait until Saturday evening and it will be beautiful.

All coastal areas can expect high surf, possible beach erosion and rip currents, especially Thursday through Saturday.

Given the average uncertainty in track and intensity forecasts, the map below shows the probability of locations experiencing tropical storm force winds (sustained 40mph+) over the next five days.  But there are a couple things to keep in mind with Arthur: the track is more certain than average, and the coastal cities will experience its left or weak side.

Probability of experiencing tropical storm force winds from Wednesday morning through Monday morning. (NOAA)

Probability of experiencing tropical storm force winds from Wednesday morning through Monday morning. (NOAA)

Late last night, a nascent eye finally formed and was visible on satellite as well as radar… as of this morning, the center is located about 95 miles due east of Cape Canaveral and it is crawling north at 5 mph. The storm is also being heavily monitored by both the Air Force’s C-130 and NOAA’s P-3 aircraft; they continuously probe the storm to measure its central pressure, wind field, and environment to assist with current analysis and to provide forecast model input.

Composite radar image from 9:30am EDT showing Arthur looming off the Florida coast. (Weather Underground)

Composite radar image from 9:30am EDT showing Arthur looming off the Florida coast. (Weather Underground)

One limiting factor for strengthening that is evident from satellite, radar, and aircraft data is that a significant amount of dry air is getting wrapped into the storm’s circulation to the west and north, choking off its gasps for moist tropical air.  So despite sitting over the warm waters of the Gulf Stream and encountering barely any vertical wind shear, it will have a hard time intensifying until the influx of dry air relaxes.  In this enhanced satellite image, high clouds (cirrus and the tops of strong thunderstorms) are white, low clouds are yellow, and the land/ocean is brown-ish.  You can clearly see the north and west sides of the storm are sparse with thunderstorm activity.

Enhanced satellite image from 8:45am EDT.  (NOAA)

Enhanced satellite image from 8:45am EDT. (NOAA)

Kudos to the National Hurricane Center

Coincidentally, two significant milestones were achieved yesterday at the National Hurricane Center, both the result of years of research and testing.  First, a graphical five-day tropical weather outlook was introduced.  Although it’s not all that exciting right now, the product will display any active storms or disturbances as well as areas where formation (“genesis”) probability is low, medium, or high over the next five days.   Making this a skillful operational product was no small task, and a lot of credit goes to forecasters at NHC as well the general advances made by numerical models.

Secondly, and of more relevance right now, a real-time, high-resolution, consistent, national map of storm surge flooding is being produced for public consumption for the first time. Again, this was no small feat but should prove to be a very valuable tool for emergency managers as well as forecasters and the general public.  The storm surge inundation values shown on the zoomable map are valid through the next three days, and have just a 10% chance of being exceeded (according to the surge model).  A real example from this morning is shown below for the Wilmington, NC area.

Storm surge inundation forecast for the Wilmington, NC region. (NOAA)

Storm surge inundation forecast for the Wilmington, NC region. (NOAA)

For additional surge mapping along the entire eastern seaboard, follow this link: Experimental storm surge maps

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