Why revise Hurricane Andrew ?
Hurricane Andrew's revision is a part of "The Atlantic
Hurricane Database (HURDAT) Re-analysis Project" (NOAA/NASA Grant
#GC02-093) that the author is Principal Investigator for. The goals of
this project are to extend the database back in time and to revisit
and possibly revise all of the tropical storms and hurricanes back
to 1851 of the Atlantic Ocean, Gulf of Mexico and Caribbean Sea,
including Hurricane Andrew. This database is utilized in a wide
variety of ways: climatic change studies, seasonal forecasting, risk
assessment for emergency managers, analysis of potential losses for
insurance and business interests, and development/verification of
official National Hurricane Center and compter model predictions of
track and intensity.
Unfortunately, this Atlantic hurricane database contains many
systematic and random errors that need correction. Additionally, as
our understanding of hurricanes has developed, analysis techniques
have changed over the years at NHC, leading to biases in the
historical database that had not been addressed. Finally, recent
efforts led by the late Jose Fernandez-Partagas to uncover previously
undocumented historical hurricanes in the mid-1800s to early 1900s
have greatly increased our knowledge of these past events, which also
had not been incorporated into the hurricane database.
Andrew is just one of the hundreds of hurricanes that we are
revising. It is a special case, naturally, because of the huge societal
impact that it had in South Florida. While Hurricane Andrew would have
been examined sequentially in this project sometime in late 2004 or
early 2005, I was asked by the Director of NHC, Max Mayfield, to put
Andrew at the front of the list for re-analysis because of its
significance, because of the new research findings of the wind
structure in strong hurricanes and because of its ten year anniversary.
One example of a very practical aspect of the outcome of Andrew's
re-analysis is the potential impact on building codes and insurance
rates. Previously, Hurricane Andrew was assessed as a Saffir-Simpson
Category 4 hurricane hitting Southeast Florida (comprised of
Miami-Dade, Broward and Palm Beach counties). During the 20th Century
when we have had relatively complete records, four Category 4
hurricanes were noted to have hit the area - Andrew, the 1926 Great
Miami hurricane, the 1928 Lake Okeechobee hurricane and the 1947
Broward hurricane. This gave an average "return period" of 25 years
(100 years/4 strikes) for the Southeast Florida for Category 4
hurricanes, though these occur rather unevenly within the 100 years.
However, with Andrew being re-classified as a Category 5, this is the
only one to have struck the area in (at least) 100 years. ("At least"
because records before 1900 are too sketchy for confidence in the
intensity of hurricanes that hit south Florida.) Thus the return period
is equal to or greater than 100 years for a direct strike on the
region by an Andrew-intensity (Category 5) hurricane.
So if one is interested in what the return period of extremely
devastating hurricanes (as the public, government agencies, insurance
companies and building code designers are), the category assigned is
quite important. If - as it was until recently - Andrew is denoted a
Category 4, then these are rare events (about four times in a century).
But with Andrew being re-classified as a Category 5, this indicates
that the type of destruction that Andrew caused is an extremely rare
event - with a return period much longer than previously thought.
Certainly not all the changes to tropical storms and hurricanes
in this re-analysis project are going to have as big an impact as
Hurricane Andrew's. But the intensity and track assigned to Hurricane
Andrew and the other 1273 tropical systems since 1851 is much more
important than just keeping the records accurate. It should have a
direct impact on how buildings are constructed and what insurance
rates ought to be. Please feel free to contact me for more
information about Hurricane Andrew's re-analysis or other storms that
will be looked at in the database.
Chris Landsea, September 2002
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