Coastal Development vs. Hurricane Frequency

Hurricane Irma near peak intensity on September 5, 2007  (Source: NOAA)

NOAA recently issued an “El Nino Watch” with a 50% to 55% chance of an El Nino event developing by the end of November.  But, that increases to 65%-70% during the 2018-2019 winter season.  El Nino conditions typically make environmental conditions less favorable in the Atlantic Ocean for tropical storm and hurricane development.

According to NOAA, an “average” Atlantic hurricane season has 12 tropical storms, 6 of which become hurricanes, including 3 major hurricanes (Category 3 or higher on the Saffir-Simpson Scale with sustained winds of 111/+ mph).  However, the Atlantic Ocean has had an uptick in frequency of tropical storms and hurricanes since 1995.  During that time, the Atlantic Ocean’s seasonal average has been nearly 15 tropical storms and 7 – 8 hurricanes, including between 3 and 4 major hurricanes.

By comparison, the Atlantic Ocean generally had a quieter than average cycle in terms of overall number of tropical storms and hurricanes during the previous 23-year period from 1971 - 1994.  The seasonal average during this time was between 9 –10 tropical storms, including roughly 5 hurricanes with 1 – 2 major hurricanes.  The Atlantic Ocean had no more than 3 major hurricanes in any season from 1971 to 1994, while the Atlantic had 4 or more major hurricanes 11 times since 1995.

This predominantly quieter than average period in the tropical Atlantic from the 1970s through the early 1990s is significant since that’s when a significant amount of coastal development occurred in Gulf Coast States and up the East Coast.  With a below average number of tropical storms and hurricanes, it was more common for a significant amount of new construction to be built below the standard building codes for hurricanes as a cost-saving shortcut.  Unfortunately, that’s proven to be more costly in the long-run.

Hurricane Andrew was the only major hurricane of the 1992 Atlantic hurricane season, but it was a Category 5 storm that was the costliest natural disaster in U.S. history for more than a decade.  Andrew helped expose the fact that building codes either weren’t followed for the most part or were inadequate.

Coastal development in the United States has only continued to increase in recent decades.  That has coincided with the busier than average cycle that has been underway in the Atlantic Ocean since the mid-1990s.  Consequently, landfalling tropical storms and hurricanes have been more damaging than in previous decades.  For example, Florida and the East Coast had more landfalling major hurricanes in the 50 year-period through 1965, than in the following 50 years, but the coastal population and degree of development was appreciably less prior to the 1970s and 1980s.  

The fact is that a hurricane season doesn’t have to be active to be destructive.  For example, the 2010 Atlantic hurricane season featured a slew of tropical storms and hurricanes, but the United States only experience minimal impacts.  However, quieter than average seasons have produced destructive storms like Alicia in 1983 and Andrew in 1992.  Hurricane season runs from June 1 through November 30.