James Waller, Ph.D, Research Meteorologist
Any hurricane can produce wind, surge and inland flood impacts. The severity and scope of impacts is not always consistent with ratings on the Saffir-Simpson scale, particularly for surge as we have seen with Katrina (2005) and Sandy (2012).
- • Wind: For a typical wood frame structure, damage usually starts from the top of the structure and most often with the roof (trees notwithstanding). These effects can become noticeable with sustained wind speeds as low as 40 mph. For more severe wind events, wind damage will affect the walls, and in extreme cases such as Andrew or Charley, many structures will be barely recognizable following the event. Downed trees and power lines are commonly found with any tropical cyclone.
- • Storm surge: This weather event is related to many factors including wind speed over water, the area of water affected by wind, bathymetry and coastline shape. Elevated waters will ruin the interior of any coastal property. Water velocity and particularly wave activity will cause severe to complete structural damage since water weighs about one ton per cubic yard. Water damage usually begins at the bottom of a structure and becomes more severe with increasing water levels and wave height. With excessive water velocity or wave activity, the foundation itself can be dislodged resulting in structural failure. In extreme cases the property can be scoured from the foundation such as in the Mississippi Gulf coast area from Katrina. Our most recent reminder of U.S. surge impacts is from Sandy. While Sandy was a post-tropical cyclone at landfall, the size of the wind field and angle of landfall near Brigantine, New Jersey, drove a historic surge event for the area extending as far north as Massachusetts. The severity of surge impacts was equivalent to a typical Category 3 hurricane, yet the wind speeds alone did not suggest the potential for such damage.
- • Freshwater flooding: This type of flood is affected by factors such as excessive rainfall, the capacity of local storm water management infrastructure and local geography. The freshwater impacts of Hurricanes Irene (2011) and Fay (2008) were quite severe in the New England and North Florida areas, respectively. Floodwaters can ruin any structure they affect and can even cause structural damage if water velocity is sufficient. Water damage starts at the bottom of the structure and increases in severity as waters rise.
Preparation for each of these impacts and the resulting disruption to infrastructure should be an ongoing and essential process for homeowners, businesses, government agencies including the National Oceanic and Atmospheric Administration (NOAA) and the Federal Emergency Management Administration (FEMA) and, of course, the (re)insurance industry. The landfall of one or two hurricanes cannot be ruled out for any season.
Hurricane activity is projected by seasonal outlook providers to be near or below average for the 2014 season, but these providers all stress the uncertainty of their estimates. Cool sea-surface tempertures (SSTs) and a probable El Niño would indicate reduced activity. However, the strength and placement of the El Niño in the Pacific Ocean will determine how strong the suppressing effects in the Atlantic will be, and these suppressing effects are shown to be strongest in the deep tropics. Warm SSTs in the West Atlantic and northern Caribbean warrant some caution against development off the U.S. coast. Regardless of basin activity, proper preparation for at least two landfalling hurricanes is a necessity as history has shown more than once.