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.
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.