Hurricane Matthew Threat Assessment for northeast South Carolina & southeast North Carolina

National Weather Service Wilmington NC 730 AM EDT Wednesday October 5, 2016

Steven Pfaff, WCM [email protected]

Weather Forecast Office

Wilmington, NC

weather.gov/ilm | @NWSWilmingtonNC

1

New Information

Some of the operational models have changed for the weekend and now show the potential for an atypical track. This is likely a result of a trough lifting away sooner than expected thus influencing the track of the hurricane. The latest official track has been adjusted to the east by Saturday and Sunday. As a result, potential impacts are expected at the end of the week; however, they have been adjusted to account for the eastward shift. A lot of uncertainty exists with the track and the subsequent level of impacts so please do not let your guard down as the track could change. In general, low confidence exists until the computer models gain a consistent resolution of the track with successive runs.

2

Initial Look at Potential Impacts and Confidence Wind

Surge

Flooding

Tornado

Marine/ Coastal

Low

Low

Limited

Confident

Very Confident

Extreme

Impact

High

Moderate

Elevated

Confidence

3

Potential Impacts **Specific details on impacts are difficult to determine at this time given the uncertainty in the track, however, the latest advisory implies a range of impacts. Impacts would begin late Fri and persist into Sunday morning. Marine/Coastal – High to extreme impacts are possible with very large waves, dangerous boating/shipping and surf conditions, and the potential for significant erosion. Inlet entrances will be especially hazardous as well. Wind – A track off the coast would bring fringe effects, primarily to coastal areas. Moderate impacts include: some damage to roofing/siding, porches, car ports, and sheds. Large limbs and some trees, but with greater numbers where trees are poorly rooted. Scattered power outages would also be possible. Surge – Given the current track, moderate surge impacts could occur. Some of these impacts include: coastal inundation enhanced by large breakers along the barrier islands. Damage to some vulnerable buildings is possible, mainly along the ocean front where prior erosion has occurred. Some sections of near-shore roads may flood. Flooding – Many areas are saturated from recent heavy rainfall. Additional heavy rainfall would lead to flash flooding. Some rivers and streams may rapidly overflow their banks. Many roads may become flooded as well, with the potential for road failures. The delivery of drinking water and sewer services may be impacted. Tornado – The occurrence of an isolated tornado or two can affect preparedness actions during tropical events. They can cause structural damage, trees to snap or become uprooted, power outages, and communications failures. 4

Peak Wind Information

Adjusted peak sustained and peak gust swaths valid 8 PM Friday through 8 AM Sunday. Note that the peak wind timing will be greatest late Friday night into Saturday. Also, note that these winds are highly dependent on the track of the storm. Any shift to the west will bring much higher values back toward the coast. 5

Rainfall Information

Rain chances will increase during Friday ahead of the storm. Heavy rain is possible with the potential for flash flooding, especially Saturday and Saturday night.

Rainfall totals of 4 to 8 inches are expected, especially along coastal sections of northeast SC with lesser values farther inland.

6

Tropical Storm and Hurricane Wind Probabilities

The probability for Tropical Storm Winds is very similar along the entire SC coast while Hurricane Force Wind Speed Probabilities are highest across the lower SC coast. Still some scenarios that bring hurricane conditions to northeast SC and southeast NC; however, the axis of highest probabilities remains off the coast at this time. These graphics are for a 120 hour period from 2 AM EDT Wednesday Oct 5th to 2 AM EDT Monday Oct 10th.

7

Official NHC 5 Day Forecast Track The official track has shifted to the east off the Carolinas. The storm remains a major hurricane but has weakened after its interaction with eastern Cuba. Hurricane Matthew’s closest approach to northeast SC and southeast NC is expected Saturday and Saturday night. Do not focus on the exact track of Matthew as it will shift overtime. Note, this is not an impact cone. Advisory #29 5 AM EDT Wed Oct 5, 2016 Position: Movement: Intensity: Min. Pressure:

21.1N / 74.6W (65 Mi. NNW of the eastern tip of Cuba) Toward the North at 10 mph 125 MPH (Category 3) 962 MB or 28.41inches

5 AM NHC Advisory #29 Wed Oct 5, 2016 Hurricane Matthew 5 Day Forecast Cone

8 *Note: statistically, one third of the time the storm can be outside of the 5 day error cone

Model Information

Uncertainty has increased while run-torun model consistency has decreased. Many of the models now make a right turn after getting very near to the SC coast. Please refer to the official advisory from the National Hurricane Center. Note: tropical cyclones can, and do, deviate from the model consensus. As a result, please refer to the official advisory from the National Hurricane Center.

9

Key Points

The track adjustment has led to changes in potential impacts. Do not let your guard down as any adjustment to the west would support greater impacts. Rainfall will begin during Friday, while direct rainfall associated with Matthew would occur Friday night through Saturday. Rain may be heavy at times with the potential for flooding. Model consistency has decreased leading to greater uncertainty on expected outcomes regarding any surge and wind impacts. A track farther off the coast would imply lower surge and winds impacts.

NEXT PDF BRIEFING: 7 PM EDT - Wednesday October 5, 2016

10