Note this is a multi-part review of Arthur, with the focus in this post on the creation the sustained wind forecasts.
On 3 July through 4 July, 2014 Hurricane Arthur impacted portions of eastern North Carolina with strong winds and very heavy rain as it moved northeast along the Carolina coast. Arthur’s track took the storm northeast, largely parallel to the South Carolina coast and then across the far eastern portion of North Carolina including much of the Outer Banks. This was a climatologically favored track and one that forecasters are very familiar with. Given this path, the strongest winds from Arthur were confined to the eastern Coastal Plain and especially the coastal region of North Carolina. To evaluate the performance of CSTAR related research to operations activities, we wanted to briefly share an analysis of the maximum sustained winds and the maximum wind gusts from Arthur along with a sampling of the NDFD wind and wind gust forecasts.
The map below is a subjective analysis of the maximum sustained winds observed from 03 July to 04 July 2014 during the time in which Arthur impacted North Carolina. Sustained winds of 35 MPH or more were generally confined to the counties along the immediate coast or adjacent to the sounds. Observations of sustained winds of 50 MPH or more were restricted to locations close to the storm track across the Outer Banks and near Pamlico Sound. Only a few locations reported hurricane force sustained winds, they included Cape Lookout (CLKN7), a WeatherFlow observation from Pamlico Sound, and a WeatherFlow observation in Salvo.
The map below is a subjective analysis of the maximum wind gusts observed during Hurricane Arthur. Not surprisingly, the strong wind gusts covered a larger portion of eastern North Carolina compared to the sustained winds. Wind gusts of at least 35 MPH or more impacted all of the coastal region and much of the eastern Coastal Plain. Wind gusts of at least 50 mph reported across nearly all of the North Carolina coastal counties. Many locations across and near the Outer Banks reported wind gusts in excess of 70 MPH with a few locations in the southern and central Outer Banks reporting wind gust in excess of 90 MPH. The Cape Lookout station reported the strongest gust of 101 MPH just after 11 PM EDT on 3 July just as the hurricane was about to make landfall. Two WeatherFlow reporting stations observed wind gusts of 99 MPH, one at Ocracoke and the other in Pamlico Sound.
Subjective analysis of the maximum wind gusts (MPH) observed from 03 July to 04 July 2014 during Hurricane Arthur.
A snapshot of the new TCMWindTool made available for the 2014 hurricane season. Two new options are available based on results from the NC State-NWS CSTAR CSTAR project including a wind field bias correction and incorporating the WindReductionFactor grids.
At the 2013 NOAA Hurricane Conference following the 2013 hurricane season, the NC State-NWS CSTAR tropical cyclone winds research group requested additional support for their project and the ability to test some experimental methodologies and tools. Following the conference, collaborators from NWS Weather Forecast Offices (WFOs), the National Hurricane Center (NHC), the Hurricane Research Division, and the Earth Systems Research Laboratory worked together to make improvements to the TCMWindTool including implementing some of the CSTAR research results. Developers at ESRL modified the TCMWindTool and added the ability to use a Modified Rankine Error Function (MREF) wind model which was developed as a part of the NC State-NWS CSTAR project and acts as a bias correction to the TCM wind guidance. In addition, the TCMWindTool now fully integrates the NC State-NWS CSTAR project methodology of creating grids of wind reductions. With this methodology, forecasters edit WindReductionFactor grids of reductions of the TCM guidance that can vary both temporally and spatially instead of a single over land reduction that was used previously. In addition, the WindReductionFactor grid can be viewed by adjacent WFOs improving collaboration and assisting in realizing better consistency in the NDFD.
Forecasters at NWS offices in Charleston, Newport, Raleigh, and Wilmington tested these new GFE methodologies during Hurricane Arthur. During Arthur, forecasters provided mainly positive feedback on this methodology and noted the much improved consistency and an improved quality of the wind forecast s using this approach when compared to past experiences. We continue to evaluate the performance of the updated tool and methodology. While some issues were identified, the result was largely an improvement or previous methods and has made editing much easier than in the past. Some of the feedback provided by forecasters included:
• “It certainly led to better coordinated wind grids”
• “Produced realistic output”
• “The integrated tool was “even more efficient than in past years, likely due to the tweaks to the TCMWindTool.”
• “The process seemed to go well and I think the output was reasonable”
• “The tool allows for more science”
While a detailed verification of the NDFD wind forecasts is not available, most forecasters believed the process did an effective job of downscaling the TCM guidance from the NHC to produce a realistic and accurate wind filed across North Carolina. An example of some of the NDFD wind forecasts are shown in the figure below. This event demonstrated a notable CSTAR research to operation success of the new CSTAR motivated methodology.