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Hurricane season draws to a close

By: Dr. Jeff Masters, 3:23 PM GMT on November 30, 2009

It's November 30, and the inconsequential Atlantic hurricane season of 2009 is in the books. Residents all along the Atlantic coast can give thanks for this year's much-needed respite after the pummeling Mother Nature gave last year. The four direct deaths recorded this year represented the lowest death toll since the El Niño hurricane season of 1997, which also had four deaths. This year's season featured only nine named storms, three hurricanes and two major hurricanes, which was 61%, 38%, and 51% of the 1995 - 2008 average activity for named storms, hurricanes and major hurricanes, respectively, according to the end-of-season summary posted by the Colorado State University hurricane forecast team of Phil Klotzbach/Bill Gray. Higher than average wind shear, and lower than average relative humidity at middle levels of the atmosphere were primarily responsible for this year's reduced activity (Figures 1 and 2). These conditions are common during El Niño years, and this year's moderate El Niño undoubtedly contributed to the low levels of Atlantic hurricane activity observed. In addition, a stronger and more southerly than usual mid-Atlantic trough was active during much of hurricane season, contributing to high wind shear over the Atlantic.

Figure 1. Departure of relative humidity at mid-levels of the atmosphere (500 mb, about 18,000 feet) for the August - October peak portion of the 2009 hurricane season. Subsiding air due to El Niño conditions depressed the relative humidity up to 15% below average (red colors) over the tropical Atlantic. Image credit: end-of-season summary posted by the Colorado State University hurricane forecast team of Phil Klotzbach/Bill Gray, with data from NOAA/ESRL.

Figure 2. Departure of wind shear from average for the peak 60-day period of the Atlantic hurricane season. The August-October averaged 200-850 mb vertical wind shear across the Main Development Region (MDR, 10-20°N, 20-70°W) was 9.3 m/s, which was the highest vertical shear magnitude over this three-month period since the El Niño year of 2002. The 2009 August-October MDR value was also approximately 2 m/s greater than the 1995-2008 average vertical shear. Image credit: NOAA/CPC.

Some other notable feature taken from the Klotzbach/Gray report:

A late-starting season. Ana did not form until August 15. This was the latest "A" storm of the season since Andrew formed in 1992 on August 17. However, the 2009 season exploded into a flurry of action August 15 - 16, when the Atlantic featured a rare triple threat of simultaneous named storms beginning with the letters A, B, and C--Ana, Bill, and Claudette. The last time this occurred was in the slow-starting 1984 hurricane season, when Tropical Storms Arthur, Bertha, and Cesar were all active on September 1.

Nine named storms occurred during 2009. This is the fewest since 1997, when eight named storms formed.

27.25 named storm days occurred in 2009. This is the fewest named storm days since 1991, when only 24.25 named storm days were recorded.

Three hurricanes occurred in 2009. This is the fewest since 1997 when there were also three hurricanes.

Five named storms (Ana, Danny, Erika, Fred, and Henri) dissipated over the open ocean in the tropical and sub-tropical Atlantic this year. This is a fairly rare occurrence that typically only occurs in years such as this year that are characterized by high levels of tropospheric vertical wind shear.

11.25 hurricane days occurred in 2009. This is the fewest hurricane days since 2002 when 10.75 hurricane days were reported.

2 major hurricanes formed during the 2009 hurricane season. The last time that fewer than two major hurricanes occurred in a season was in 1997 when only one major hurricane (Erika) formed.

3.25 major hurricane days occurred in 2009. This is the fewest major hurricane days in a season since 2006 when only two major hurricane days were recorded.

The season accrued an Accumulated Cyclone Energy (ACE) of 50. The 1951 - 2005 average is 102.3, and the 2009 ACE was the lowest since 1997 (41) and the 16th lowest of the last 66 years since the aircraft reconnaissance era began in 1944.

No Category 5 hurricanes developed in 2009. This is the second consecutive year with no Category 5 hurricanes. The last time that two or more years occurred in a row with no Category 5 hurricanes was 1999-2002.

No named storms formed in June or July. The last time that no storm activity occurred in June or July was 2004 (Alex formed that year on August 1). This is the 18th year of the past 66 years with no storm formations in June or July.

August had above-average ACE activity. 29 ACE units were recorded during the month, which is approximately 125% of the 1950-2000 average.

58% of seasonal ACE was generated during the month of August. The last time that more than 58% of seasonal ACE was generated during the month of August was in 1942.

September was very quiet with only 11 ACE units generated during the month. This is the quietest September since 1994 when only 3 ACE units were recorded.

No ACE was generated between September 13 and October 4. The last time that this occurred was 1991. Prior to that, one has to go all the way back to 1925 to see no ACE generated during three of the most active weeks of the Atlantic hurricane season.

October was also very quiet with only 2 ACE units occurring. This is the quietest October since 1994 when no tropical cyclone activity occurred.

Only 13 ACE units occurred during the combined September-October period. This is the fewest ACE units during this two-month period since 1994 (3), and the fifth fewest since the aircraft reconnaissance era began in 1944.

Hurricane Bill generated 26 ACE units, or 52% of the seasonal total. The last time that one storm generated that much of the seasonal total was Erika in 1997 which generated 63% of the total ACE observed that year.

Hurricane Fred became the third storm on record to reach major hurricane status east of 35°W, although prior to 1972 when Dvorak satellite estimates from polar-orbiting satellite reconnaissance became routinely available, some storms may have been missed in the eastern part of the Atlantic basin.

Hurricane Ida became only the second hurricane to reach hurricane status in the Caribbean in November during an El Niño year (where El Niño is defined to be all years since 1950 where the October Niño 3.4 SST anomaly is 0.5ñC or greater). The only other storm to reach hurricane status in the Caribbean in November in an El Niño year was Martha in 1969.

Ida became the second latest tropical cyclone to make landfall along the Gulf Coast, trailing only Hurricane Kate in 1985 (which made landfall on November 21).

Only two tropical storms (Claudette and Ida) made U.S. landfall this year while no hurricanes made U.S. landfall. This is the first time since 2006 and the 13th time in the last 66 years where no hurricanes made U.S. landfall.

No hurricanes made landfall along the Florida Peninsula and East Coast. This marks the fourth year in a row with no hurricane landfalls along this portion of the U.S. coastline. The last time that we went four years between hurricane landfalls along the Florida Peninsula and East Coast was 1980-1983.

No major hurricanes made U.S. landfall this year. Following seven major hurricane landfalls in 2004-2005, the U.S. has not witnessed a major hurricane landfall in the past four years. The four consecutive years between 2000-2003 also experienced no major U.S. hurricane landfalls. Since 1995, the Atlantic basin has had 56 major hurricanes but only 10 (18%) have made U.S. landfall. The long-period average is that approximately 30% of major hurricanes that form in the Atlantic basin make U.S. landfall.

Figure 3. The eye of Hurricane Bill on August 19 at 2157 UTC, from a NOAA P-3 Hurricane Hunter aircraft flying at 10,000 feet. Photo credit: Jack Parrish of NOAA's Aircraft Operations Center.

Hurricane Bill
Hurricane Bill was the strongest hurricane of the 2009 Atlantic hurricane season. Bill peaked in intensity as a lower-end Category 4 storm with 135 mph winds. Bill was a very large storm, and had the fifth largest diameter of tropical storm force winds on record (460 miles). Bill brought tropical storm force winds of 46 mph to the Bermuda airport as the storm passed about 175 mi west of the island at Category 2 strength, during the morning of 22 August. The hurricane then recurved and turned to the northeast with increasing forward speed, brushed the south coast of Nova Scotia early on 23 August, and made landfall as a tropical storm near the Burin Peninsula of Newfoundland.

Top winds on Newfoundland were measured at Cape Race, which recorded sustained winds of 58 mph, gusting to 76 mph, between 1:30 and 2:30 am NDT on 24 August. A storm surge of 1.2 meters (4 feet) was estimated by Environment Canada for Placentia Bay where Bill made landfall. Damage was minor on Newfoundland, with no major flooding reported. Bill dumped up to three inches of rain on Newfoundland.

There were two deaths associated with Bill. A 7-year-old girl died in Acadia National Park, Maine when she was swept into the water by large waves, and a 54-year-old swimmer drowned in New Smyrna Beach, Florida in rough seas caused by Bill. The large hurricane fueled high waves over a large portion of the Atlantic basin for several days. The Meteorological Service of the Dominican Republic reported that these waves produced coastal flooding and damage along the north coast of the Dominican Republic. Reports from Environment Canada indicate that in Nova Scotia power outages were common (tens of thousands of residences lost power) and there were road wash-outs and localized fresh water flooding. Coastal flooding from surge and waves was widespread along much of the Atlantic coast. On Long Island, NY, beach damage was severe; in some areas the damage was the worst since Hurricane Gloria in 1985. Along the coasts of North Carolina, waves averaging 10 ft (3.0 m) in height impacted beaches. In Wrightsville Beach, up to 30 rescues were made due to strong rip currents and large swells; however, only one incident resulted in hospitalization. Severe beach erosion took place at Bald Head Island, where 150 ft (46 m) of beach was washed away, resulting in the loss of the remaining sea turtle nests.

Figure 4. Radar reflectivity image of Tropical Storm Claudette as it approached landfall just southeast of Fort Walton Beach shortly after midnight on 8/17/09.

Tropical Storm Claudette
Tropical Storm Claudette made landfall at about 1:15 am EDT August 17, 2009, near the eastern end of Santa Rosa Island, just southeast of Fort Walton Beach in Florida. Claudette's top winds were around 50 mph. A Personal Weather Station in Eastpoint, FL recorded sustained winds of 49 mph, gusting to 66 mph as Claudette approached the coast. Heavy rains of 3 - 4 inches were confined to a narrow strip of coast, and Claudette did not cause any major flooding. Apalachicola received just over 4 inches of rain so far from Claudette. One death is being blamed on Claudette, a drowning off the Florida Panhandle coast.

Figure 5.. Hurricane Fred at peak strength, 8:55am EDT UTC 9/9/09. At the time, Fred was a Category 3 hurricane with 120 mph winds. Image credit: NASA.

Hurricane Fred
Fred became only the fourth major hurricane on record in the far southeastern portion of the Atlantic basin (south of 30°N and east of 40°W) and is the only hurricane on record in the basin with an intensity greater than 100 kt when located south of 30°N and east of 35°W. However, it is important to note that prior to 1972 (when routine Dvorak classifications from polar-orbiting satellites began), it would have been difficult to assess the intensity of most tropical cyclones in this part of the Atlantic basin.

Figure 6. Tropical Storm Ida at 1 pm EST November 5, 2009. In this MODIS image captured seven hours after landfall, Ida was a tropical storm with 65 mph winds. Image credit: NASA.

Hurricane Ida
Hurricane Ida made landfall over eastern Nicaragua on November 4 as a Category 1 hurricane with 75 mph winds--the first November Atlantic hurricane to make landfall in an El Niño year since 1925. Ida intensified at one of the fastest rates on record as it approached Nicaragua. It took just 24 hours from when the first advisory was issued for Tropical Depression Eleven until Ida reached hurricane strength. Since reliable satellite measurements began in 1970, Hurricane Humberto holds the record for fastest intensification from first advisory issued to hurricane strength--18 hours. (Actually, Humberto did the feat in 14 1/4 hours, but this was rounded off to 18 hours in the final data base, which stores points every six hours). Ida is now tied for second place for fastest intensification from first advisory to hurricane strength. There have been six other storms that accomplished the feat in 24 hours.

Ida survived its crossing of Nicaragua, and intensified once it emerged over the Caribbean, eventually reaching Category 2 strength over the Gulf of Mexico as it headed northwards towards the U.S. Gulf Coast. High wind shear and cool water temperatures caused Ida to weaken dramatically before landfall in Alabama, and Ida made landfall near Dauphin Island, Alabama at 5:40 am CST November 10, as a tropical storm with 45 mph winds. Winds at coastal locations during Ida's landfall were mostly below tropical storm force. One exception was Dauphin Island, where winds peaked at 40 mph, gusting to 50 mph, near midnight. Radar-estimated rainfall from Ida showed many regions received 3 - 5 inches of rain, which caused some minor river and street flooding. The main damage from Ida seems to have been beach erosion, as a 3 - 6 foot storm surge topped by battering waves affected a long stretch of coast, from Southeast Louisiana to the Florida Panhandle. Ida drove a 5.5 foot storm surge to Shell Beach, LA (on the east side of New Orleans). Ida was responsible for one death, a 70-year-old fisherman who knocked off of his boat in the Mississippi River by a wave as Ida approached.

The remnants of Ida merged with a Nor'easter that developed off the coast of North Carolina, and the Ida-energized Nor'easter brought the highest storm surges on record to the Atlantic coast between Norfolk, Virginia, and Lewes, Delaware.

Next year's hurricane season?
The Colorado State hurricane forecast team will be issuing their forecast for the 2010 Atlantic hurricane season on Wednesday, December 9. Expect them to forecast a more active season. Since 1950, there have been 17 El Niño events, and only one of them lasted through two full hurricane seasons. Thus, we can expect neutral or La Niña conditions for next year's hurricane season, which should lead to much higher levels of activity than in 2009.

In my previous post, on the Manufactured Doubt industry and the hacked CRU emails, I mistakenly referred to the George C. Marshall Institute as the George C. Marshall Foundation. I have corrected the error, and apologize for the confusion. The George C. Marshall Institute is an organization active in the Manufactured Doubt campaign against human-caused global warming, while the George C. Marshall Foundation is a charitable organization celebrating the legacy of the great American general and Secretary of State, George C. Marshall.

Major storm brewing for the Gulf Coast
There's a major extratropical storm brewing over the northern Gulf of Mexico that could be as damaging as Tropical Storm Ida was, for the Gulf Coast from New Orleans to the Florida Panhandle. The storm is expected to hit Tuesday through Wednesday. A storm tide of 4 - 6 feet is forecast for the Florida Panhandle, 3 - 5 feet for the Alabama coast, and 3 - 4 feet for the New Orleans area. Consult the NOAA extratropical storm surge forecast page for forecasts of the storm surge from this event. I'll have a new post Tuesday and/or Wednesday to discuss this storm.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.