Friday, August 26, 2011

Update on Hurricane Irene Impacts: North Carolina

The above visible satellite image shows Irene continuing to hold good form as she slowly advances toward the Carolinas. At 5pm EDT, the center of Irene was located approximately 265 miles South/Southwest of Cape Hatteras, and moving Northward at 14 mph.  Maximum sustained winds remain between 100 and 105 mph.   I still anticipate at least slight strengthening this evening or tonight as the center of Irene passes through the warm waters of the Gulf Stream.  This up-tick in intensity also continues to be forecast by the computer models as well...

Regardless of whether Irene has sustained winds of 105, 110 or even 115 mph on Saturday, the impacts along the coast and inland across North Carolina and southeast Virginia will be significant.

Tropical storm force winds have already been observed along the South Carolina coast this afternoon, and are spreading Northward up into North Carolina at this time.  A fan of my facebook page, Melissa Ham, was kind enough to give me this link to an awesome live webcam at Wrightsville Beach, North Carolina.  It's being buffeted around by tropical storm force winds and heavy rain right now.  The radar image below from Charleston shows squalls with heavy rain continuing to advance Northward into the regoin around the Northwest side of Irene:

Hurricane force winds will then overspread the region during the overnight hours and into early Saturday morning.

At this time, it appears that the center of Irene will pass directly over the Pamlico and Albemarle Sounds (somewhere between Cape Hatteras and Williamston) by midday on Saturday.  The image below is the GFS computer forecast model, valid 2pm EDT Saturday:

Another computer model, called the HWRF, valid at the same time and zoomed-in tightly on the Carolina coast shows the center heading in the same general direction, but a little bit slower on this model:

While the two models differ slightly on the exact position of the center at 2pm tomorrow, the do agree on the geographical track, and they also both forecast Irene to be stronger at that time than she is now.  The GFS is forecasting a maximum surface wind of 115-120 mph, while the HWRF is forecasting a maximum surface wind of 130 mph.  Both of the models forecast Irene to intensify tonight and tomorrow morning as she moves across the Gulf Stream (as a pointed out a few paragraphs above).

I am in the camp that believes she will undergo at least modest intensification in the Gulf Stream tonight and Saturday morning.  Lets assume that she does intensify but go with the lowest sustained winds estimated by the above 2 models, at 115 mph.  That refers to the maximum sustained wind, which would take place within 30 or so miles of the center, across the Outer Banks, the sounds and adjacent portions of the mainland (mainly East of Highways 13 and 17, to the East of a roughly Murfreesboro to Jacksonville line).

To the West of that line, up to I-95 and I-40, sustained winds of hurricane force, with gusts up to 85 or 90 mph can be expected.  From there on back as far as the Raleigh-Durham and Fayetteville areas, sustained winds of tropical storm force (40-50 mph) with gusts to 60 mph will be a strong possibility.

I apologize for the crudeness of the image above, I just wanted to try and get this information out there as quickly as possible, as folks across this region should be rushing preparedness plans to completion at this time.  As I pointed out way up at the top of the post, winds will increase to tropical storm force across this region this evening and early tonight, then reach hurricane force in the indicated areas by late tonight or early Saturday morning (spreading from South to North).  The maximum sustained ranges and gusts indicated on the image above would likely take place beginning from mid-morning (in the South) to late afternoon (in the North) on Saturday, and based on the expected movement of the system could last from 6-9 hours in any given area.  As you can see, this will not be a short-lived event with respect to very strong, potentially damaging winds.

As I pointed out in my post concerning this region yesterday evening, the grounds are already saturated from recent rains.  An additional 6-12 inches of rain will fall across this region with Irene, about half of which could well take place even before the stronger winds arrive on Saturday.  Trees, many of which are already loaded with moisture, will become even more saturated while sitting within saturated (if not flooded) grounds.  All of these factors will come together when the winds arrive to produce widespread tree damage, which will also increase the threat for widespread power outages across the region.  If you don't already own a generator and think that you can find one at this late hour, it may prove to be a very wise investment...

Storm surge will be another issue with Irene.  The image below is called an "inundation map" and shows the forecast maximum impact of storm surge flooding by Irene:

The red shaded areas suggest 9-11 feet of water in those areas, while the orange and yellow shaded areas suggest 5-9 feet of water can be expected due to storm surge.  The image below is a close-up view of the area that is currently forecast to have the greatest surge impacts:

Heavy rainfall will also induce flash flooding in many areas, with 10-14 inches of rain currently forecast for the Eastern half of this area tonight through Saturday night.  

For additional information on specific local evacuation orders and expected storm surge magnitudes, please go to this link and select the office nearest you.

Hopefully folks across this area have heeded the warnings this week and are well prepared (if not heading West) to handle Irene.  

I'll have a full East Coast-wide update on Irene in a short while, along with updates for the Baltimore/Washington, New York City/New Jersey and New England areas later this evening...

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