09 October 2013

South Florida hurricane climatology... and major hurricane landfall drought

I wanted to take today to revisit a post that I made last year... and is still just as relevant. The first part focuses on hurricane landfall climatology in south Florida, one of the most vulnerable and frequently-hit areas in the country.  The second part briefly takes a look at the continued absence of major hurricane landfalls on the U.S.

As we head further into October, the fifth month of the official Atlantic hurricane season, it’s very important for folks in south Florida to realize that this is the greatest hurricane risk month. More hurricanes directly hit or affect southern Florida in October than in any other month. In the graphic shown below, the gray circle is 300 miles across and centered on far western Broward County – designed to include all of southern Florida and immediate surrounding ocean. Any storm of hurricane intensity (sustained winds of 75mph+) whose center passed within that circle is shown in the colored lines, and the legend in the lower right corner associates the color with a category on the Saffir-Simpson scale (yellow is Category 1, orange is Category 2, etc). Finally, the coastal counties are shaded by historic landfall frequency, with darker reds corresponding to more frequent, and pale reds corresponding to less frequent. The monthly tally of tracks passing through the circle is indicated in parentheses below the month. Keep in mind that all of these storms were hurricanes – tropical storms and depressions are not included; and most importantly, never focus on exactly where the center of the track is. Destructive winds, tornadoes, flooding rains, and inundating storm surges can and do occur for hundreds of miles away from the center; so even tracks on the fringe of the circle likely brought severe weather conditions to the mainland.

Another interesting aspect of these maps is that in August and September, southern Florida is most likely to get struck by a storm coming from the southeast. But in October, the dominant direction is from the southwest… due to storms coming from the Gulf of Mexico and western Caribbean, the more favored areas for hurricane formation later in the season.

On the topic of landfalls, do you remember the last time a major hurricane made landfall on the U.S.? It was Hurricane Wilma, on the morning of October 24, 2005, and it hit southwestern Florida at Category 3 intensity. That was 2,908 days ago, an utterly unprecedented span between major U.S. hurricane landfalls. 

Going back to 1900, this graph shows the number of days between consecutive major hurricane landfalls on the U.S.  This helps to put the current span in perspective.  (Adapted from http://rogerpielkejr.blogspot.com)
Streaks that even approach this long are very rare, and only two other spans of over 2,000 days have occurred since 1900. Why has it been so long? Pure luck. There have been several major hurricane landfalls since 2005 in other countries (Nicaragua, Mexico, Cuba, Virgin Islands, Bahamas, and close encounters in Jamaica and Belize), so it definitely isn’t correct to say that seasons since 2005 have been quiet … far from it. No one knows exactly when our lucky streak will end, but I can say with 100% certainty that it will end eventually!

If one does not occur during the remainder of the 2013 season, then looking ahead to August 1, 2014 (for example) would bring the span up to 3,204 days.

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