Tag Archives: 2018 North Atlantic Hurricane Season

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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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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Central Gulf Coast Waits for Gordon’s Arrival

With alerts ranging from hurricane warnings to storm surge and flood watches, the central Gulf Coast states from Louisiana to the western counties of the Florida Panhandle await the arrival of Tropical Storm Gordon.

Located only 130 miles offshore of Mobile, Alabama, the outer rain bands of Gordon are beginning to bring deteriorating weather conditions to the Florida Panhandle and central Gulf coastline. A band of deep convection near its well-defined surface center and increased lightning activity near the inner core is indicative of an organized system with the potential to intensify. This is reflected in the latest National Hurricane Center (NHC) advisory, which calls for Gordon to be a Category 1 hurricane when it makes landfall in the north-central Gulf of Mexico coastline later tonight. Gordon looks set to be first hurricane to hit the contiguous U.S. this year, though it is not the first named system to threaten the central Gulf coastline; Alberto affected Louisiana and Alabama earlier in the season as a subtropical storm.

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Hurricane Season Outlook: Are We Heading for a Repeat of 2017?

With the 2018 Atlantic hurricane season underway, the (re)insurance industry is still reflecting on the events of last year. The 2017 season will be remembered as one of the most active, damaging, and costliest seasons on record, and specifically for the impacts of three storms: Harvey, Irma, and Maria.

RMS followed its longstanding strategy of delivering thoughtful and thorough analysis of all available data sources when responding to the events of 2017, including the use of instrumentation and in-person RMS staff research and reconnaissance.

For Harvey, we provided insight into our event response with regular updates from across the organization and outlined how we deployed the new RMS® U.S. Inland Flood HD Model in real-time to support a pipeline of flood deliverables for our clients. And for Maria, the use of the latest modeling innovations, up-to-date exposure and vulnerability data supported by on the ground presence and local knowledge helped us to provide clients with a clearer picture of post-event losses across the islands impacted.

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Recapping a Memorable 2017 Atlantic Hurricane Season

RMS has released its 2017 North Atlantic Hurricane Season Review documenting one of the most active, damaging, and costliest seasons on record. The 2017 season saw a total of 17 named storms, with ten of these storms reaching hurricane strength and occurring consecutively within a hyperactive period between August and October. The season will be remembered for its six major hurricanes and specifically for the impacts of three of these storms: Harvey, Irma, and Maria.

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Impact of the 2017 North Atlantic Hurricane Season on the RMS Medium-Term Rate

In my years of contributing to this blog, I have written extensively about the long-standing debate about the current state of hurricane activity in the North Atlantic Basin. This debate has become no clearer following the 2017 hurricane season; one of the busiest and costliest seasons on record. 2017 followed a stretch of below- to near-average seasons that began in 2012 and it is unclear whether future seasons will remain active or return the recent level of relative quiet.

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Early Riser: Does a Busy 2017 Equate to an Early Start for North Atlantic Hurricanes in 2018?

Although my colleague Peter Holland declared the Atlantic hurricane season officially closed, there are reports in the media that environmental conditions in the North Atlantic basin may be favorable enough to sustain tropical cyclones, potentially adding to what has already been a very active year and perhaps foretelling an early start to hurricane activity in 2018.

The official hurricane season for the North Atlantic runs from June 1 to November 30 and encompasses over 97 percent of annual climatological activity. Out-of-season tropical systems — events happening through December to May — are rare, but not unprecedented. The U.S. National Oceanic and Atmospheric Administration (NOAA) Hurricane Research Division (HRD) states that since 1851, 88 storms have been observed in the Atlantic during the off-season — that’s about one out-of-season storm every two years. In theory, this could be an underestimate, as the peer-reviewed literature suggests an undercount of Atlantic tropical cyclones prior to the satellite reconnaissance era.

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