Tuesday, September 29, 2009

Hurricane Watch: "Slowest September in the tropics since 1997"

Worldwide, Accumulated Cyclone Energy (ACE) is approaching, and Northern Hemisphere is at, 30-year record lows, see second link*. From Ken Kaye's Storm Center:

Assuming no more storms form by Wednesday, this will be the slowest September, tropically speaking, in 12 years.

That would be since 1997.

Only two named systems have emerged this month, including Tropical Storm Erika and Hurricane Fred.

Pretty incredible, considering September is historically the most active month, seeing on average 4 named storms, including two hurricanes.

Again, the main reason this month – and the season so far – has been relatively calm: El Niño, which has created storm suppressing wind shear.

In September 1997 (another El Niño year, by the way), only one system developed: Hurricane Erika (pictured at right). Like this year’s Fred, it reached Category 3 strength.

All told, only seven named storms formed in 1997. Amazingly, no systems formed at all that August, normally a busy month....MORE

From Ryan N. Maue, Florida State University:
*September 11: After two years (2007-2008) of dramatically below normal Northern Hemisphere and Global hurricane activity, 2009 has actually (year-to-date) managed LESS Accmulated Cyclone Energy! 2009 is currently the second slowest Northern Hemisphere ACE year-to-date behind 1981 in the past 30-years. Here is a text list of the previous September 11 to-date totals for NH ACE. LIST

...Tropical Cyclone ACE Update

Figure: 24-month running sum of tropical cyclone accumulated cyclone energy for the entire globe (top black squares / time series) and the Northern Hemisphere only (bottom green squares / time series). The difference between the two time series is the Southern Hemisphere total. Data is shown from January 1979 - August 15, 2009 mainly because intensity estimates of SH cyclones are often missing in the JTWC best-tracks prior to 1980. See notes.

Figure: 24-month running sums of tropical cyclone ACE for a combination of basins of the Northern Hemisphere. The Western North Pacific, Eastern North Pacific, and the Northern Indian Ocean typically sees more activity than the Eastern Pacific and North Atlantic combined. However, during the strong La Nina event of 1998-1999, the very quiet WPAC TC activity was exceeded by the NATL and EPAC combined. The two time series are correlated at R = 0.56 but of course are not independent....MORE