Preliminary 2011 Hurricane Season tracks for the Gulf of Mexico (click to enlarge)
Preliminary 2011 Hurricane Season tracks across the Gulf of Mexico. Green dot=tropical wave. Red dot=Tropical Depression. Open symbol=Tropical Storm.

Review of the 2011 Atlantic Hurricane Season
Déjà Vu All Over Again?

Big Season, Few Impacts; Valley Escapes with Glancing Blows from Tropical Storms

Overview
As the 2011 Atlantic Hurricane Season winds to a close, many in North America are breathing a sigh of relief once again. While the number of cyclones, hurricanes, and major hurricanes was enough to put fear into coastal residents from the Virgin Islands to the Canadian Maritimes, steering patterns, persistent wind shear, and recalcitrant dry air high in the atmosphere reduced the potential impact that might have been had steering currents favored more landfalls, and deep atmospheric moisture been readily available. Media coverage may focus on a busy season that was missing in action; however, unlike 2010, when major population centers around the United States Gulf and Eastern Seaboard saw virtually no impact, Hurricane Irene (late August) kept the eastern megalopolis from Philadelphia to Boston on its toes. Click here for a satellite time lapse of the 2011 season.

Irene will be remembered in different ways depending on location. From the Jersey Shore through New York City, Irene was a wake–up call to preparedness and potential danger, while it did not live up to the "hype" for many residents" expectations. For residents of the Outer Banks of North Carolina, it was a stronger version of 2010’s Earl, causing a bit of damage similar to other storms in the past twenty years. For the mountains of New Jersey, New York, and Vermont, Irene will be long remembered for devastating flash and river flooding. The majority of the $10 billion in damage was related to the floods. After Irene, only Tropical Storm Lee caused trouble, focusing flooding rains and damage along the Louisiana Gulf Coast. Remnants of Lee, absorbed into an atmospheric trough of low pressure, produced a significant flood across New York and Pennsylvania, where summer rains had saturated the ground.

Rio Grande Valley: Close, but no Cigar
Record Water Year (2011) drought was guaranteed when the potential for significant rainfall dried up, literally, in persistent northwest to west flow bringing dry air from the Southwest U.S. and northern Mexican desert regions, around the La Canícula ("Dog Days") high pressure ridge. While a number of cyclones threatened the western Gulf, only Nate (mid September) was able to reach hurricane status. The season began with some promise, as a strengthening Tropical Storm Arlene brought bands of rainfall totalling between 1.5 and nearly 3 inches to the Lower RGV on June 30th. Later that afternoon, spin from the decaying cyclone may have contributed to a rotating thunderstorm which briefly dropped an EF–1 tornado between Pharr and Hidalgo. A month later, Tropical Storm Don fizzled into what some called "Tropical Storm ‘Dud’", bringing around inch of rain along the coast but nothing to the mid and upper Valley.

Tropical Storm Lee (Labor Day Weekend) and Hurricane Nate (September 8/9) not only missed the Valley, but dry air to the west and north of each storm exacerbated the drought through stifling heat and lower humidity. Lee brought triple digit record heat to the coast; Nate was shoved south of Tampico by the persistent ridge, leaving the Valley high and dry once again.

Fast Facts

  • NOAA’s May 2011 Hurricane Outlook forecast 12 to 18 named storms, 6 to 10 hurricanes, 3 to 6 major hurricanes, and an Accumulated Cyclone Energy (ACE) Index Range of 105 percent to 200 percent of average. The preliminary results so far:
    • 12 tropical storms.
    • 7 hurricanes.
    • 3 major hurricanes.
    • ACE estimate: 119 percent of average
  • The combination of high upper oceanic heat content across much of the basin, and a neutral El Niño rapidly returning to a weak La Niña in the eastern tropical Pacific, were important reasons for the large number of cyclones.
  • The season got off to a very slow start. At one point, the Atlantic basin had five named tropical storms while the Eastern Pacific basin had five named hurricanes. In fact, the first eight storms (Arlene through Harvey) failed to reach hurricane status for the first time since records began in 1851. On the other hand, five of the final six cyclones were hurricanes.
  • Teleconnections, or atmospheric "puzzle pieces" which help dictate intraseasonal weather patterns, likely played a role in storm formation and movement. Some situations were eerily similar in 2011 when compared with 2010:
    • Flow around the broad central Atlantic Ridge and repeating troughs nearing the east coast (below) recurved all but one (Harvey) Cape Verde wave
    • Cyclones forming in the western Caribbean (Rina) or southern Gulf (Don, Lee, Nate) were blocked by the La Canícula ridge and/or impacted by a combination of atmospheric dry air and wind shear
    • A persistent negative North Atlantic and Arctic Oscillation may have contributed to the stability of the eastern North American trough
  • The 2011 season, like the one before it, is proof positive why we don’t "do" seasonal landfall predictions. As stated on the NOAA Hurricane Season Outlook: "NOAA does not make seasonal hurricane landfall predictions. Hurricane landfalls are largely determined by the weather patterns in place as the hurricane approaches, which are only predictable when the storm is within several days of making landfall."

 

Average 500 mb geopotential height for the tropical western Atlantic during the peak of the 2011 hurricane season (click to enlarge)
General steering patterns for the peak of the 2011 Hurricane Season (August to October; click to enlarge).
Preliminary 2011 Atlantic hurricane season track map, without Irene
Preliminary 2011 Hurricane Season track, entire Atlantic basin, without Irene. The final track map will include Irene and be posted well after the season. Legend is the same as in image at top of page (click to enlarge).

The following table summarizes the 2011 Atlantic Hurricane Season.

Preliminary 2011 Hurricane Season Statistics
Tropical Storm Arlene   June 29 - July 1 65 903 0.2234 1.63
Tropical Storm Bret   July 17 - 22 65 996 None 2.95
Tropical Storm Cindy   July 20 - 23 70 994 None 2.31
Tropical Storm Don   July 27 - 30 50 997 None 1.62
Tropical Storm Emily   August 1 - 7 50 1003 0.005 1.99
Tropical Storm Franklin   August 12 - 13 45 1004 None 0.283
Tropical Storm Gert   August 13 - 16 65 1000 None 1.85
Tropical Storm Harvey   August 18 - 22 60 994 Minimal 1.24
Hurricane Irene 3 August 20 - 28 120 942 10.1 20.3
Tropical Depression 10   August 25 - 26 35 1007 None --
Tropical Storm Jose   August 28 - 29 45 1007 None 0.528
Hurricane Katia 4 August 29-September 10 135 946 0.157 24.8
Tropical Storm Lee   September 1 - 5 60 986 1 1.71
Tropical Storm (Unnamed)   September 2 40 Unkn None --
Hurricane Maria 1 September 6 - 16 80 979 Unkn 8.74
Hurricane Nate 1 September 7 - 11 75 994 Unkn 3.83
Hurricane Ophelia 4 September 21-October 3 140 940 Unkn 18.4
Hurricane Philippe 1 September 24-October 9 90 976 None 14.8
Hurricane Rina 2 October 23 - 28 110 966 Unkn 9.07
Tropical Storm Sean   November 8 - 12 65 983 None 3.33
Totals         11.484 119

Orange and bold rows indicate cyclones that impacted the Rio Grande Valley. Dates listed indicate the time the cyclone was deemed tropical, including initial depression stage.

For final details on the 2011 Atlantic Hurricane Season, check the National Hurricane Center’s Atlantic Season Archive.


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