Dorian looks set to pass over the northern Bahamas in the coming days as
potentially a Category 5 major hurricane, but forecasts regarding future U.S.
impacts remain significantly uncertain, with the latest guidance providing a
twist in the tale that no one anticipated a few days ago.
Understanding the Uncertainty: A Matter of Timing
The meteorological situation that Hurricane Dorian finds itself in is as fascinating as it is uncertain. Several days ago, Florida was bracing itself for potentially its third major hurricane landfall in as many years. Now, Dorian looks more likely to make landfall in the Carolinas, or, as some models increasingly suggest, it may recurve soon enough that is misses the U.S. entirely. So, why have the forecasts been so uncertain? It’s all to do with timing.
Every twist and
turn of a real-time hurricane can affect global financial markets, public
safety, or government and international aid agencies that provide assistance. Within
the (re)insurance space, the ability to understand forecast track, timing, and potential
hazard and loss impacts before landfall helps entities to prepare and execute
their event response processes effectively. This includes having adequate
capital to cover claims, setting up claim centers and planning policyholder
outreach, securing and positioning adjusters in areas that are likely to be
impacted, and determining what, if any, risk can be ceded to reinsurance or
clients, the traditional approach to quantify potential impacts ahead of a
landfalling storm involves selecting similar storms from the RMS® North
Atlantic Hurricane (NAHU) stochastic event set. While this generates vital
insights that can be extracted quickly from internal databases, there are
opportunities to provide earlier and more comprehensive insights into the storm
ahead of landfall.
To date, RMS clients have also benefited from real-time analysis of hurricane events through RMS HWind Real-Time Analysis products. These observation data-based snapshots and footprints have provided the industry with a standard “ground truth” representation of tropical cyclone wind field size and intensity before, during, and following landfall effectively helping to describe what the storm is doing and what the storm has done.
Co-authors: Michael Kozar, Senior Modeler, RMS HWind; James Cosgrove, Senior Analyst, RMS Event Response
Michael underwent rapid intensification in the two days leading up to landfall, reaching the Florida Panhandle coastline as a strong Category 4 major hurricane with maximum sustained wind speeds of 154 miles per hour (247 kilometers per hour), according to the RMS HWind real time service. At landfall, Michael had a tight inner core and its strongest winds were located just 14 miles (22 kilometers) south-southeast of the center of the storm near Mexico Beach. Tropical storm force winds extended up to 115 miles (185 kilometers) eastward along the Panhandle coastline to Pensacola.
Whilst the Saffir-Simpson Hurricane Wind Scale (SSHWS) is exclusively based on maximum sustained wind speeds, which often only covers a very small part of the system, the Integrated Kinetic Energy (IKE) metric conveys the intensity, size, and structure of the storm’s wind field into one number and has become a useful metric for comparing the destructiveness of storms. Using the IKE metric, we can compare and contrast Hurricane Michael to other events in the RMS HWind historic archive.
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).
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.
As we are approach the more active part of hurricane season in late August, most of the action so far has been taking place in the Central Pacific with Hurricane Hector passing to the south of the Hawaiian Island chain a couple weeks ago. Now, Hurricane Lane is projected to pass much closer to Hawaii and this time the U.S. National Oceanic and Atmospheric Administration (NOAA) has sent in the “big guns”. In addition to “Gonzo” — NOAA’s Gulfstream jet (NOAA has an agreement that allows them to name their aircraft after Sesame Street characters), the Lockheed Orion P3 “Kermit” is also on duty in Hawaii to fly research missions into Hurricane Lane. Kermit brings an arsenal of scientific sensors including the airborne Doppler radar and the Stepped-Frequency Microwave radiometer (called the “Smurf”) and a supply of GPS dropsondes to launch into the storm.
Challenging conventional thinking pays dividends with regards to assessing hurricane risk. And as the current North Atlantic Hurricane Season marches on, here are five points — some of which are insights from last year’s active season, that can help you to reframe and potentially rethink your view of hurricane risk.
1. Hurricane Threat Is Not Just from Wind or Storm Surge
In many respects, Hurricane Harvey was the standout hurricane from last year’s trio of notable events in Harvey, Irma and Maria. The severe amounts of rainfall from Harvey — more than fifty inches (127 cm) in some areas over southeast Texas in August 2017 — certainly differentiated this event.
In 2014, Robert Muir-Wood, chief research officer at RMS, wrote a blog posing the question whether water, and not wind is the primary driver of hurricane risk and corresponding losses. With events like Harvey in 2017, Robert’s viewpoint becomes more and more valid. Although Harvey was a category 4 hurricane at landfall, around 90 percent of the estimated losses were from inland flooding. The dominance of flood-driven losses in recent events — whether they be caused by storm surge, precipitation, or both — argues for a full hurricane catastrophe modeling solution. If tropical cyclone-induced rainfall is not included as a modeled peril, there is every chance of missing a large contribution of total loss for events like Harvey.
Michael Kozar, senior modeler – Model Development, RMS
Hurricane Nate continues to race towards the central Gulf Coast today. The hurricane has become significantly better organized in the last several hours, and now has maximum sustained winds in excess of 90 miles per hour (144 kilometers per hour) based on the RMS HWind snapshot at 18:00 UTC today. This surface wind analysis is based upon data collected from the National Oceanic and Atmospheric Administration and U.S. Air Force Reserve Hurricane Hunters in addition to some surface and satellite-based observations.
Michael Kozar, senior modeler – Model Development, RMS
The latest track probability analysis of the current model forecasts has been released by the RMS HWind team, based on forecast models initialized at 12:00 UTC Friday, October 6. Using this new proprietary track forecast probability product from RMS HWind provides unique insight into the likelihood of where a storm might go, and helps to deliver insights beyond what is available from public sources.
Jeff Waters, product manager – Model Product Management, RMS
Mark Hoekzema, chief meteorologist, Earth Networks
As we have already seen during the 2017 North Atlantic hurricane season, tropical cyclones such as Harvey, Irma, and Maria cause an array of impacts to homes, businesses, and people, each with varying drivers of damage and recovery timelines. The resulting effects from these and other events reinforce the importance and value of preparedness and responsiveness when managing hurricane risk.
Having an accurate view of the extent and severity of hurricane hazard is imperative in informing effective event response strategies — both throughout a real-time event, and for efficient claims management processes afterwards. It can help insurers anticipate claims locations, counts and overall impacts to their book, where power outages and business interruption are likely to occur, where to deploy claims adjusters of various experience levels, and identify where fraudulent claims are likely (or unlikely) to occur.