Tag Archives: North Carolina

Hurricane Florence: Field Reconnaissance Findings

Introduction

After a major hurricane or a similar natural disaster, RMS routinely sends modelers and engineers into the affected region to survey the destruction. This field reconnaissance in the immediate aftermath of an event serves several purposes:

  • Provides an indication of the most prevalent type of damage (e.g. shingle loss, structural failures, flooded contents, etc.)
  • Provides an indication of the general frequency (e.g. one in five homes have shingle loss) and severity (e.g. 20 percent of shingles missing) of the damage.
  • Helps to understand the full geographic extent of the event including the subperils (e.g. wind, surge, inland flood, etc.). As part of this effort, RMS will measure flood depths (based on visible watermarks) that help provide a sanity check for the surge and flood modelers developing the event footprints.
  • Talking with locals (both homeowners and businesses) provides a better understanding of the severity of the storm and the conditions immediately after an event that may have already been cleaned up before our team arrived.

Of course, RMS is always concerned about the safety of its personnel and waits until it is safe to send anyone to the disaster areas. We also have to make sure that we can travel to the different areas affected by the disaster without too much difficulty.

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Hurricane Florence: Rainfall up to a 1,000-year Return Period

Florence’s much anticipated landfall occurred at 11:15 UTC (7.15 a.m. local time) today, Friday, September 14, near Wrightsville Beach, North Carolina, as a Category 1 hurricane. Florence remains just within the Category 1 hurricane classification on Saffir-Simpson Hurricane Wind Scale (SSHWS); as of the 18:00 UTC National Hurricane Center (NHC) advisory today, maximum sustained winds were 75 miles per hour (120 kilometers per hour). Previous observations showed that at Cape Lookout there were sustained winds of 83 miles per hour (133 kilometers per hour) and gusts of 106 miles per hour (170 kilometers per hour). Florence is now moving slowly toward the west at near five miles per hour (7 kilometers per hour).

Over the coming 36 hours, Florence is expected to meander into northern South Carolina and then progress further inland across the western Carolinas and into the Appalachian Mountains through the early part of next week.

The expectation that surge and inland flooding, rather than wind, would be the primary hazards associated with Florence was quickly realised as the storm approached the Carolinas coastline yesterday.

Excessive rainfall and dangerous storm surge present the greatest threat over the next few days. The potential for heavy rainfall has extended to the south and west given the change in projected track over the last 48 hours. Projections of over 15 inches (380 millimeters) of rain now cover much of southern North Carolina and northeast South Carolina — much of North Carolina is expected to receive in excess of six inches (152 millimeters) of rain.

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Florence: A New Twist in the Tale

No hurricane landfall forecast is simple. But looking back at the forecast tracks for Hurricane Florence from the National Hurricane Center (NHC) and the ensemble members of the leading global forecast models a couple of days ago, what stood out was how relatively straightforward they were. Florence was anticipated to make a steady, assured progress directly towards the Carolinas, make landfall, and move directly inland.

In a somewhat remarkable turn of events that few, if any, models predicted 48 hours ago, Florence is now expected to stall over, or very near to, the Carolina coastline.

The huge shift in the forecast guidance is the anticipated result of a reduction in Florence’s steering flow due to two competing areas of high pressure. The hurricane is currently being steered across the southwestern Atlantic Ocean towards the southeastern U.S. around the southeastern periphery of a mid-level ridge centered northeast of Bermuda. As the system approaches land, it will come under increasing influence from a competing mid-level ridge that is forecast to begin building over the east-central United States later today. The net result of these competing steering flows will see Florence slow, meander, or even become stationary for possibly 48 hours before the system moves ashore.

This possibility could bring prolonged hurricane-force winds and storm surge throughout Saturday and Sunday, to coastal areas along North and South Carolina, and significant inland flooding to whole region.

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Fixated on Florence

It seems somehow fitting that a storm underwent rapid intensification today, the peak of the North Atlantic hurricane season. Indeed, as forecast, Florence grew impressively from a tropical storm to a  powerful Category 4 major hurricane — as of 1600 UTC on Monday, September 10, — with maximum sustained winds near 130 miles per hour (195 kilometers per hour), according to data from a recent National Oceanographic and Atmospheric Administration (NOAA) reconnaissance aircraft mission into the storm.

A ridge of high pressure is guiding Florence on a west-northwest to northwest path across the southeastern Atlantic Ocean between Bermuda and the Bahamas towards the southeastern U.S. Swells generated by Florence are already affecting Bermuda, with warnings of life-threatening surf and rip current conditions.

With each advisory, the chances of the storm missing the U.S. is rapidly narrowing. Most global models call for a landfall over the Carolinas as a major hurricane. Although the latest National Hurricane Center (NHC) “cone of uncertainty” includes the possibility of landfall between South Carolina and southern Virginia, there has been a strong, consistent guidance that a landfall over North Carolina is the most likely scenario. RMS HWind now shows that the two cities with the highest probability of greatest impact are both in North Carolina: Jacksonville and Wilmington.

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