A few preliminary notes on this year

1
A few preliminary notes on this years hurricane
season
Klaus Wolter NOAA-Earth System Research Lab
University of Colorado at Boulder-CDC
klaus.wolter_at_noaa.gov
2010 active, but a bit underwhelming A
testable hypothesis ENSO link to late season
activity
Boulder, 23 November 2010
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2010 Hurricane Season
As expected, this was a hyper-active season
both in terms of number of named storms (19) and
hurricanes (12) - each tied at second since
1948 In terms of major hurricanes, this one
produced five, tied in 9th-14th place, similar to
ACE which is the 12th highest since 1948 this is
quite high (top 20 or so), but maybe a little
less than expected In terms of Cat 5
hurricanes, there was none, dropping the ranking
down below those 20 out of 63 years with such
hurricanes more unusually, landfalling
hurricanes in the U.S. were conspicuously absent
this is only the 15th time out of 63 years that
we did not have a landfalling hurricane. In
fact, this is the record-highest ACE season
without having a landfalling hurricane ( 1951 is
a distant second ranked season of this type).
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A testable hypothesis
Why did we not get our fair share of
landfalling hurricanes, as widely expected in the
light of a very high forecast number of
storms? If you compare the number of named
tropical storms in different parts of the North
Atlantic vs. the number of landfalling storms, it
is obvious that storms that form in the Gulf of
Mexico have a much better chance of hitting the
U.S. coastline than storms that form immediately
off the coast of West Africa. In fact, of the
138 named systems from 1948-2009 that formed in
the Gulf of Mexico, a full 100 ended up making
landfall in the U.S. (72.5). This compares to
storms in the Main Development Region (281) of
which 67 made landfall (23.8) in the U.S., and
only one out of 7 such storms that formed to the
east (lt20W) of the MDR (14.3). 2010 ended up
with 12 hurricanes, half of which formed as
tropical storms to the east of 60W. Only two
storms formed in the Gulf of Mexico, both failing
to attain hurricane status. Could the lop-sided
distribution of tropical storm formation have
been a factor in 2010? Was this driven by
unusually warm SST off the coast of West Africa,
or was it more a function of unusual atmospheric
circulation features?
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ENSO link strongest with mid-late season
Summer-to-fall ENSO conditions (MEI) relate best
to the hurricane count after September 1st.
However, it is mostly the depression of such
hurricanes in El Niño situations that stands out
(i.e., the early end of the season) rather than a
strong La Niña signal.