03 November 2005

perspectives on the 2005 ATL season

From Gary Padgett: 
One perspective on this season which I've found very interesting
is that the superabundant activity has been largely due to the
incredible amount of activity in July and October.   I've calculated
the Net Tropical Cyclone activity index (NTC) per Dr. Gray's
formula for each month from 1950-2004, and for the months
of this hurricane season.

(The NTC is an average of the six "cardinal" parameters---number of
named storms (NS), hurricanes (H), intense hurricanes (IH), and the
total number of days accumulated for each intensity level (NSD, HD,
IHD)---with each expressed as the percentage of the long-term average
over some baseline period.   The NTC for each month is calculated
by dividing that month's total NS, H, etc by the annual averages of
each parameter, then averaging the six percentages.)

The following table gives the average monthly NTC for the months
June - October for the period 1950-2004, followed by the 2005
NTC for that month:

Month     Avg. NTC    2005 NTC
Jun             2%          4%
Jul             4%         64%
Aug            25%         39%
Sep            48%         70%
Oct            16%         63%

The core months of Aug/Sep produced a total of 10 NS
with 7 H for a combined NTC of 109%.    While having
two hurricanes of the intensity of Katrina and Rita was
very unusual, otherwise the activity of the two main months
wasn't particular all that remarkable.   Many years have
had Aug+Sep totals of 10 NS and 7 H---last year had
12 NS and 8 H with an NTC of 208%.

October's is the highest NTC since 1950 (61%) and is
only the 3rd October on record to produce 6 NS, the
others being 1950 and 1887.

July's NTC of 64% wildly exceeds the previous high
July NTCs of 26% (1996) and 24% (1966), and the
5 NS forming during the month is a new record.

Please visit my tropical Atlantic headquarters.

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