Hurricanes and Tropical Storms: Higher Frequency for the Future?
by Jim Cato, Florida Sea Grant Director
 
September 29, 2005 -- Katrina, Jeanne, Frances, Charley and Ivan are familiar names to all of us. Unfortunately, they are not the names of our children or grandchildren coming for a summer visit. But based on historical records, Gainesville and other parts of Florida can expect them and their friends to visit more often over the coming years, and yes, decades.
 
Much about hurricanes and tropical storms has been spoken and written regarding their impacts during the last few years. Certainly, the human and economic impacts of these natural events have become more devastating as our coastal populations have increased dramatically. If history repeats itself, the state will have more storms and be in more frequent recovery mode for the next few decades.
 
Analysis of storm records from more than 100 years show that multi-decadal cycles exist in the frequency of hurricanes (maximum sustained surface winds above 74 miles per hour) and tropical storms (maximum sustained surface winds from 39-73 miles per hour). A 1992 article in the Bulletin of theAmerican Meteorological Society by William Gray and Christopher Landsea indicates that seasonal and multi-decadal variations of intense hurricane activity on the U.S. East Coast are closely associated with above average seasonal and multi-decadal summer rainfall amounts in certain regions of Western Africa. Periods of higher rainfall there cause a larger number of U.S. East Coast storms. Another 2001 article authored by at team of researchers led by Stanley Goldenberg, in Science attributed the recent increase in hurricane activity in the Atlantic Basin to simultaneous increases in North Atlantic sea-surface temperatures and changes in the speed of winds at different altitudes.
 
The cycle of Florida storms based on historical records is approximately 60-70 years from peak to peak. The cycle is also geographic in nature. Over a period of years, hurricanes and tropical storms tend to make landfall in a particular region. For example, from 1971-80, Florida was hit by only four storms of tropical storm strength or greater, while the coast from Texas through Alabama received 12 storms. Gray and Landsea’s article indicates that Gulf of Mexico storms are highly dependent upon meteorological conditions in the Western Caribbean and the Gulf of Mexico. For an example of charted storm tracks in Florida since 1871, see the 2002 edition of “Florida Hurricanes and Tropical Storms,” by John Williams and Iver Duedall, University Press of Florida, or track your own at NOAA's Coastal Services Center.
 
The chart above shows the number of hurricanes and tropical storms that made landfall in Florida by decade, from 1871 to 2000, and for the first half of the current decade. The chart also shows the number of hurricanes and tropical storms that passed within 100 miles of Gainesville. The storm may have been a hurricane at one time, as occurred with Frances and Jeanne in 2004, but downgraded to a tropical storm by the time it passed near Gainesville. The damage, however, was still significant and the message is still the same. How many times have you heard (until last year) that Gainesville is too far inland, too far north, or pick your favorite reason, to really be affected by hurricanes or tropical storms? Not true -- Gainesville can sustain major damage from a hurricane or tropical storm.
 
Florida’s (and Alachua County’s) population is now growing at a record pace. From 1960 to 1990, the time of the lowest frequency of hurricanes and tropical storms in Florida on record, Florida’s population grew from 4.6 million to 12.9 million. Alachua County grew from 74,100 to 181,600 residents during the same period. This means that about two-thirds of Florida’s population became residents during the least active hurricane period on record. Perhaps they have been lulled into a false sense of security about the potential impacts of hurricanes and tropical storms.
 
By most indications, however, Floridians can anticipate more severe weather and increasing devastation. The current population of Florida is about 17.5 million; by 2025, the population is predicted to be about 23 million. Today, almost 80 percent of Florida’s population lives in the 35 coastal counties (of the 67 total counties in the state). Almost 80 percent of the state’s economic activity occurs in these coastal counties. Everyone is learning fast that Florida (and Gainesville) will experience more storms over the next 20-30 years if historical trends repeat. The cycle appears to be repeating itself based on the previous decade and due to the pace of storms to date in the current decade. Since there will be huge numbers of new residents in the state, most of them locating on the coast, the impact of an increased number of storms will be much more dramatic, from both a personal safety and an economic perspective (see table below).
 
According to a June 2005 report issued by John Marburger, III, Science Advisor to the President, since 1900, hurricanes and tropical storms making landfall on the U.S. Gulf Coast have caused more than 9,000 deaths and more than $100 billion in damages (adjusted to 2004 dollars) to homes and property. The 2004 series of major storms affected 15 states and cost billions of dollars in damages. If early estimates hold true, the economic damage caused by Katrina could equal about 25 percent of the cost of all storms to date, and add a substantial number of deaths to the 9,000 total from all earlier storms.
 
If the frequency of storms returns to historical levels, then the loss in human lives and economic value has the potential to be staggering.

			Population at end of period shown
	Florida*	Within 100 miles of Gainesville*	Florida**	Alachua County**
Four decades (1871-1910)	20.0 per decade; 2.0 per year	8.5 per decade; .85 per year	752,619	34,305
Two decades (1911-1930)	11.0 per decade; 1.1 per year	4.0 per decade; .4 per year	1,468,211	34,365
Three decades (1931-1960)	17.0 per decade; 1.7 per year	7.3 per decade; .7 per year	4,951,560	74,074
Three decades (1961-1990)	8.3 per decade; .8 per year	2.6 per decade; .3 per year	12,938,071	181,596
1991-00	18 over one decade; 1.8 per year	4 over one decade; .4 per year	15,982,824	217,955
2000-05	9 over 6 years to date; 1.5 per year to date	5 over 6 years to date; .8 per year to date	About 17 million	About 245,000

* Calculated from chart and NOAA Coastal Services Center
** UF Bureau of Economic and Business Research