The Cone on the Map: Hurricane Risk Management

Hurricane Ian (photo: NOAA, via Wikipedia)

In the wake of Hurricane Ian, risk communication is in the news again.

The Washington Post had an article about the limitations of the hurricane forecast cone (Scott Dance and Amudalat Ajasa, "The confusion and controversy over the forecast cone," October 5, 2022).  Rebecca Morss, from the National Center for Atmospheric Research, said "Some people think the cone represents the size of the storm, which it doesn't.  Some people think it represents the area of impact, which it doesn't."

5-day Forecast Track, 8:00 P.M., September 25, 2022 (Source: NOAA).

The deficiencies of this single graphic were significant because the forecast hurricane track changed rapidly in the days before landfall, as the National Hurricane Center's archive shows.  At 8:00 P.M. on Sunday, September 25, 2022, the line in the middle of the five-day cone crossed the Big Bend area of Florida, approximately 300 miles north of Fort Myers.  At 8:00 P.M. on Monday, as the hurricane approached Cuba, the line in the middle of the three-day cone crossed the west coast of Florida just north of Tampa Bay, and Fort Myers was just outside the edge of the cone.  By the next morning, that line crossed the coast just south of Tampa Bay.  By Tuesday evening, the line had moved to Port Charlotte, and Fort Myers was inside the cone.

The miscommunication was preventable.  As mentioned in The Washington Post article, the forecast cone graphic includes the disclaimer: "Note: The cone contains the probable path of the storm center but does not show the size of the storm.  Hazardous conditions can occur outside of the cone."

Also, the National Hurricane Center publishes numerous other graphics that do indicate the expected size of the storm: the Hurricane-Force Wind Speed Probabilities is a particularly useful one.  On Sunday evening, this graphic showed the probability of hurricane-force winds in Fort Myers was at least 10%.  By Monday evening, this probability had increased to at least 20%.  By Tuesday morning, it was at least 40%.

To me, because I am familiar with it, the hurricane forecast cone is useful, but it clearly has limitations, and I don't rely on it, especially when my family is in harm's way.  The media can better inform the public by showing the wind-speed probability and storm surge graphics and emphasizing the reach of the storm instead of focusing on where the center of the storm makes landfall.  

The Hurricane Ian archive includes a Graphics Archive that will present a slideshow of the graphics, which is useful for seeing how the forecasts changed.

Deciding to Save New Orleans

Ten years after Hurricane Katrina, the city of New Orleans has done much to mitigate the risk of a hurricane.  The August 22 issue of The Washington Post included an article by Chris Mooney (http://www.washingtonpost.com/sf/national/2015/08/21/the-next-big-one/) about an important decision that remains to be made: whether to use sediment diversion to protect the wetlands that protect New Orleans.  In addition to slowing the loss of wetlands, the advantages include a relatively low one-time cost and a potential economic value from sportsmen and tourists who would enjoy the wetlands.  The key disadvantage is the disruption to the local fishing industry.  A key uncertainties are whether the diversions will actually work because there are many factors that influence wetland restoration and the impact of the wetlands on the storm surge may be limited.

The decision-making process appears to be an analytic-deliberative one: a state advisory board has scientific experts, while fishermen have organized a group to oppose the diversions and (if necessary) block construction, and a state agency needs to make a decision before the end of the year.