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.
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