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Hurricane Season a Dud in the Atlantic and Globally Lowest in at Least 30 Years

By Joe D'Aleo
Monday, October 26, 2009


Despite a recent more normal flurry in activity in the tropical Pacific, the global activity continues its multi-year decline. A
tlantic temperatures affect the frequency and strength of Atlantic tropical activity.

Atlantic temperatures undergo a cyclical warming and cooling with a period of about 70 years (indicated by the Atlantic Multidecadal Oscillation or AMO). The warming in 1995 saw an immediate pop in the number of storms. That warming and activity peaked in 2004 and 2005 the years of the very active hurricane seasons.










But the AMO has declined dramatically in the last two years. It was even negative early this year. This argued for a quieter year. An El Nino also developed and favored a quiter Atlantic season due to increased shear.









Hurricane Season 2009 has had through mid October, 8 storms, two hurricanes. Most storms were short-lived. Hurricane Bill was the exception.

  • Tropical Storm Ana
  • Hurricane Bill
  • Tropical Storm Claudette
  • Tropical Storm Danny
  • Tropical Storm Erika
  • Hurricane Fred
  • Tropical Storm Grace
  • Tropical Storm Henri

The two hurricanes:



Hurricane Bill



Hurricane Fred



For the global picture we turned to FSU’s Ryan Maue's activity update pages.

In the eastern Pacific, Rick became a super Hurricane CAT 5. The eastern Pacific is more active than the Atlantic. Indeed we have 18 storms to date there.




Ryan Maue's Seasonal Tropical Cyclone Activity Update



With the Northern Hemisphere Tropical Cyclone (TC) seasons winding down in the Eastern Pacific and North Atlantic, it is as good a time as any to take account of what the Earth has offered during the past 12-months in terms of TC Accumulated Cyclone Energy (ACE). Since the last Southern Hemisphere season was quite uneventful with well-below normal ACE, and the continued Northern Hemisphere inactivity, the sum of the two = global ACE has fallen off the table.

Accumulated Cyclone Energy (ACE) valid October 14, 2009 18Z

The current ACE represents the tropical cyclone activity from January 1, 2009 until the date indicated. This is readily compared to the YEARLY value which is the previous 30-year average from Jan 1 - Dec 31 or the calendar year. The values through October 31 and November 30 represent the previous 30-year average as well with the average October ACE indicated in the last cell. There is considerable year-to-year variability across the basins, of which understanding motivates the updating and maintenance of this site.

BASIN

2009 CURRENT

30-YR AVG
ALL YEAR

30-YR AVG
THRU OCT 31

30-YR AVG
THRU NOV 30

30-YR AVG
OCTOBER

N Hemisphere

325

563

494

543

90

N Atlantic

44.3

106

99

105

14

W Pacific

184

309

255

292

57

E Pacific

93

132

130

132

18

N Indian

5

17

10

15

2

S Hemisphere

107

~200-230

Out of

Season

---


Comparisons through October 12

What is the current state of tropical cyclone activity compared to the same date during the past 30-years? This comparison table highlights the GLOBAL, SOUTHERN HEMISPHERE, and NORTHERN HEMISPHERE totals for the previous 12 and 24-months, respectively.

BASIN

CURRENT 12 [24] MONTH TOTAL

30-YR AVG 12 [24] MONTH TOTAL

NORTHERN HEMISPHERE

347 [807]

563 [1126]

SOUTHERN HEMISPHERE

103 [296]

206 [412]

GLOBAL TOTAL

450 [1103]

769 [1538]


Note: The Accumulated Cyclone Energy metric combines frequency, duration, and the intensity of tropical cyclones into one value that can be calculated from historical storm records as well as current operational center (i.e. NHC) advisories. The ACE is simply the wind speed squared (times 10^4 kts^2) for each 6-hour storm location and intensity estimate -- added up for an entire season or whatever period you wish to define. CLIMO based upon 1979-2008 climatology.

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