The risk posed by hurricanes that stall upon landfall may be growing, according to analysts at TigerRisk, whose comments come as Tropical Storm Barry bears down on New Orleans.
The reinsurance broker noted that the frequency of such storms appears to have increased, with back-to-back hurricanes in 2017 and 2018 stalling after crossing the coast.
Hurricanes Harvey and Florence both caused unprecedented levels of flood damage due to the unexpected and unrelenting rainfall that they dumped after coming ashore.
Harvey was the second costliest hurricane in US history, causing losses of $125 billion (of which $19 billion were insured), while Florence resulted in overall losses of $45 billion (of which only $4.6 billion were insured).
Now, with Storm Barry creeping towards Louisiana at just 5mph, experts are warning that the storm could stall and bring devastating flooding to some regions.
Residents in New Orleans are already dealing with flash flooding after heavy rainfall this week, and there are concerns that storm surge from Barry could cause the Mississippi River to spill out over its levees.
However, after conducting an extensive review of weather data as far back as 1851, analysts at TigerRisk say there is no evidence that the frequency of stalled storms has increased.
“Our research identified 37 tropical storms that had stalled once they had come ashore,” said Anna Neely, Research and Development Analyst at TigerRisk. “Only in six cases did they occur back-to-back in consecutive years.”
Nevertheless, even if storms continue to stall at the normal rate, the increasing dollar amount of damage caused points to the inadequacy of flood control and insufficient flood insurance.
“Considering the growing exposure in coastal areas, the risk from stalling hurricanes may be growing even if the frequency is not,” TigerRisk’s report stated. “More research is required to understand the unique risks posed by these kinds of storms which are sure to reappear in the future.”
Atlantic tropical cyclones are classified as stalling if they make landfall with at least tropical storm strength, and if they have forward speed of 6mph or less for at least 12 consecutive hours.
The cyclone also needs to stall inland within 100 miles of the coast or 50 miles out to sea, and produce wind speeds of 40mph or more on average during the stall period.
Storm Barry is currently approaching the US coast with wind speeds 65mph, with experts saying there is a strong chance that it could ramp up to the 74mph speeds required for it to be classified as a hurricane.