Tag Archives: florence; hurricane florence

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 Update: September 13

Over the last 24 hours, the structure and forecast track of Hurricane Florence has evolved significantly as the storm begins to impact the Carolinas, but the material wind, storm surge and flood threat it poses to the Southeastern and Mid-Atlantic U.S. remains.

As of 1200 UTC yesterday (September 12), Florence’s wind field was large and powerful as the storm inched closer to the U.S. coast through favorable environmental conditions. According to RMS HWind analyses, which utilize more than 30 public and private observational data sources to generate objective, ground-truth-based tropical cyclone wind field analytics, maximum 1-minute sustained winds were estimated to be 124 miles per hour (199 kilometers per hour) (Figure 1 below), placing the storm squarely in the Category 3 range on the Saffir Simpson Wind Scale.

In addition, the Integrated Kinetic Energy (IKE), an indicator of tropical cyclone strength and damage potential, was estimated to be 104 Terajoules (TJ), putting it on par with historical events like Frances (2004), Gustav (2008), and Isabel (2003).

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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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Hurricane Florence: A Rare Event

The forecasts for Hurricane Florence have been unusually consistent this far in advance of an anticipated landfall, projecting its path to cross the coast of the Carolinas at major hurricane intensity. For some perspective, if we look at the historical hurricane record since 1850, we find major hurricane landfalls are quite rare along this part of the U.S. Atlantic coastline:

RMS Reconstructed Loss values are based on wind and storm surge damage to present-day exposure, and not on trending forward historical losses

Over the past 167 years, there have been just nine major hurricanes that made landfall along the coast of North and South Carolina. So, on average we can expect one major landfall along this 490-mile stretch of coastline every eighteen and a half years. Certainly, a rare event. Only three of these storms — Hazel, Gracie, and Hugo — were Category 4 (on the Saffir-Simpson Hurricane Wind Scale) at landfall. There has never been a Category 5 landfall north of Florida.

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