26 October 2016

No — hurricane intensity is not exaggerated to scare people

This post is a joint effort with my long-time friend, colleague, and fellow CWG contributor, Phil Klotzbach.  We discuss why a hurricane's peak winds are rarely, if ever, observed by a weather station or buoy in this Capital Weather Gang post:

No — hurricane intensity is not exaggerated to scare people

25 October 2016

"Major Hurricane" Amnesia in the U.S.

October 24th marked the 11-year anniversary of the last "major" hurricane to make landfall on the United States.  On the morning of October 24, 2005, Hurricane Wilma hit the southwest Florida peninsula as a Category 3 storm, and since then, no other hurricane Category 3 or stronger has made landfall on the U.S. -- a span that is unprecedented in the historical records.

Hurricanes are rated solely by the strongest wind speed found in the storm, not by size, rainfall, storm surge, fatalities, cost, or whether or not they make landfall. A major hurricane is conventionally defined to refer to a Category 3, 4, or 5 on the Saffir-Simpson Hurricane Wind Scale... those storms which from an engineering perspective will create "devastating" or "catastrophic" damage to buildings, trees, and infrastructure.  The term "major" is not a socio-economic label, it applies to hurricanes anywhere based on their peak winds.

Since Wilma, there have been 29 major hurricanes observed in the Atlantic, 11 of which made landfall as major hurricanes on other countries, including Mexico, Cuba, Bahamas, Haiti, Nicaragua, and Bermuda.  The U.S. has just gotten lucky to the point where 11 hurricane seasons have gone by and none of those 29 major hurricanes have crossed our shores.

Tracks of 27 of the 29 major hurricanes that have been observed in the Atlantic since Hurricane Wilma.  Hurricanes Gaston and Matthew from 2016 are not shown.
There have been close calls, most notably Ike in 2008, which made landfall near Galveston with peak wind speeds just shy of the Category 3 threshold.  Sandy in 2012 hit Cuba as a major hurricane, but by the time it made landfall on New Jersey, it was not technically a hurricane anymore, and even if it had been, it would have been a Category 1 storm. Recently, Matthew was a very close call... it hit Haiti and Cuba at Category 4 intensity, and was a Category 4 hurricane just off the Florida coast, but the eye and eyewall remained offshore, sparing coastal cities the worst of the storm's fury and avoiding an official landfall.  By the time it made landfall in South Carolina, it was a Category 1 storm.

A hurricane of any intensity is going to be destructive if it makes landfall somewhere.  By the time a tropical cyclone is organized enough to be classified as a hurricane, it is a significant storm capable of producing inundating storm surges and tremendous rainfall if it is near land.  It does not take a "major" hurricane to do those things -- Ike, Irene, Sandy, and Matthew prove that point well.  In fact, over 75% of all hurricane-related fatalities in the U.S. are caused by storm surge and rainfall, while just 8% are linked to wind.  This is why it is never a good idea to shrug off a hurricane because it's "only" a Category 1.  There's more to the story than the category! 
Fraction of tropical cyclone related fatalities in the U.S. caused by various factors from 1963-2012. (Rappaport 2014)
So why make a distinction between Category 1-2 hurricanes and Category 3-4-5 hurricanes?  Once sustained wind speeds reach over 110 mph, the damage caused by wind increases notably and dramatically.  Then, in addition to the water-based problems cause by storm surge and flash flooding, you also have widespread power loss, roof removal/damage, uprooted trees, etc.

If you have experienced the devastation caused by just the water-based facet of Category 1-2 hurricanes such as Ike, Irene, Sandy, and Matthew in the U.S., you can appreciate that a hurricane of any intensity means business.  But the stakes are increased even higher when the destructive wind speeds are added from a Category 3+ hurricane.

The 2016 season ends in five weeks, and something could still happen to end the U.S.'s major hurricane "drought", but the odds are historically very slim in November... so the record span will likely reach well into 2017.

12 October 2016

Hurricane Nicole heading for Bermuda

Nicole formed eight days ago, just as Matthew was hitting Haiti and Cuba, so its existence was overshadowed by Matthew for much of its lifetime. But since Sunday, it has been the only active storm in the Atlantic, and is poised to strike Bermuda as a Category 2 hurricane on Thursday.

Wednesday morning sunrise on Hurricane Nicole.
As of the 8am EDT advisory, Nicole's peak winds are up to 100 mph, and it is just 320 miles from Bermuda.  "Landfall", or closest approach, is expected on Thursday afternoon, but rainbands are already reaching out to the island. A hurricane warning is in effect, and in addition to the winds, 4-8" of rain is forecast, as well as significant storm surge.

I have long, updating radar loops from Bermuda available at http://andrew.rsmas.miami.edu/bmcnoldy/tropics/radar/

Bermuda has had an unusually rough past decade compared to climatology there, with six hurricane encounters: Karl 2016, Joaquin 2015, Gonzalo 2014, Fay 2014, Igor 2010, and Florence 2006.  For a tiny speck in the ocean, I'm sure they're hoping for the unlucky streak to end after Nicole.

By the numbers, the season thus far has had 14 named storms, 6 hurricanes, and 2 major hurricanes (defined to be Category 3+ on the Saffir-Simpson scale).  Climatologically by this date, an average season would be at 10 named storms, 5 hurricanes, and 2 major hurricanes.  And then in terms of ACE, or Accumulated Cyclone Energy, the season is now at about 127% of average for October 12th.  Matthew contributed an impressive 43% of the season's total, and just two storms (Gaston and Matthew) contributed 65% of the total.

The next name on this season's list is Otto, but as of now, there is no new activity expected in at least the coming week.