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04.30.2020

What Works Better for Predicting Hurricane Damage: Wind or Pressure?

Philip J. Klotzbach Ph. D. - Research Scientist - Department of Atmospheric Science

Atlantic hurricane seasons have a long history of creating devasting storm damage causing significant financial impacts. For over 40 years, meteorologists have used the Saffir-Simpson Hurricane Wind Scale to assess storm strength and potential threat to life and property. Hurricane storm characteristics that inflict damage are not isolated to just the maximum wind speed. 

The Saffir-Simpson Hurricane Wind Scale only categorizes the hurricane wind threat, ranking storm intensity on a scale of Category 1 to 5.  The Saffir-Simpson scale does not, however, take into consideration the totality of storm impacts, including storm surge and rainfall. 

The Tropical Meteorology Project team at Colorado State University, along with colleagues at NOAA, North Carolina State University, Aon and UCAR set out to analyze existing data to assess what may be a more accurate factor in predicting hurricane strength and damage post-landfall.  Is it the maximum wind speed or the minimum sea level pressure?

This study, slated to be published in the April 2020 edition of the Bulletin of the American Meteorological Society, concluded that minimum sea level pressure (MSLP) showed a stronger relationship than maximum sustained wind (Vmax) for continental U.S. hurricane damage.  MSLP is also easier to measure, both with aircraft and surface-based measurements than is Vmax.  

CSU researchers analyzed the relationship between normalized damage by U.S. hurricanes making landfall from 1900-2018.  Researchers applied a dataset of normalized hurricane damage, looking at historical hurricane damage and adjusting that data to determine how much damage might occur today given changes in population, inflation and wealth.  

Air pressure inside a hurricane measures the storm’s intensity.  The lower the pressure, the stronger the storm.  While pressure and wind speed are strongly correlated, pressure is more of an integrated quantity that assesses the “strength” of the storm, as opposed to just the maximum wind speed at any point in the storm’s circulation.  Pressure correlates significantly with the size of the storm, which is an important driver of storm surge.  Winds are generated due to the pressure gradient between the eye of the hurricane and the surrounding environment.  A hurricane with a low pressure relative to its Vmax is an indicator that the storm is likely very large.

Typically, storms hitting the East Coast - from Georgia to Maine - tend to be somewhat larger, as hurricanes typically grow as they move northward out of the tropics.  Consequently, the maximum winds can be somewhat weaker, but these hurricanes often have low minimum sea level pressure (MSLP) and present the likelihood of significant damage upon landfall.  Pressure, however, is just a marginal improvement over wind speed for hurricane damage sustained by storms making landfall along the Gulf Coast region and in Florida.

Recent Hurricane Pressure Analysis

Atlantic hurricane seasons historically have caused massive damage and inflicted significant financial impact.  Hurricanes Harvey, Irma, Maria, Florence, and Michael combined to incur more than $345 billion (USD) in economic damage during 2017 and 2018. 

Hurricane Katrina in 2005 was classified as a Category 3 hurricane when it hit the Gulf Coast.  If Katrina would have been classified using pressure at the time of landfall it would have classified it as a Category 5 hurricane.  Katrina’s landfall was accompanied by a storm surge that reached 28 feet, inundating large portions of the Mississippi coastline and resulting in over 200 fatalities in Mississippi.  Over 1,500 fatalities occurred in Louisiana from Katrina due to storm surge and associated failure of the levees. 

In 2008, Hurricane Ike was classified as a Category 2 hurricane when it made landfall in Galveston, Texas, and over 30 individuals perished in Texas from a storm surge that reached 15-20 feet.  If Ike had been classified using pressure, it would have been a Category 3 hurricane, elevating Ike to major (Category 3+) hurricane status and giving residents additional cause to take preparedness actions.  

Superstorm Sandy was extremely large when it made landfall in New Jersey in late October 2012.  As it neared landfall, it was a Category 1 hurricane by Vmax, while it was a Category 4 hurricane by pressure MSLP.  While Sandy became post-tropical just before making landfall, its category using MSLP immediately before landfall indicated a much more powerful hurricane than would have been anticipated by its Vmax.  Sandy caused over $65 billion in damage, making it the third costliest U.S. hurricane on record – trailing only Katrina (2005) and Harvey (2017).

The CSU study finds that pressure (MSLP) is a more skillful predictor of hurricane damage in recent years than is maximum wind speed (Vmax).  For the insurance industry, more reliable metrics for potential storm damage are a key component of catastrophic weather risk management.  The general public would also be well served to be more informed and familiar with other threats posed by hurricanes than just the maximum wind speed. CSU will incorporate this study’s findings as they assess storm activity throughout the 2020 Atlantic hurricane basin season, since MSLP is an excellent metric for evaluating a hurricane’s potential damage.

Find the direct link to the CSU paper below:

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