Hurricane season draws to a close
November 30 marks the final day of the 2010 Atlantic hurricane season--a strange and highly active season. While it was an exceptionally active year, with 19 named storms, 12 hurricanes, and 5 intense hurricanes, deaths and damages were far below what one would expect from so much activity. To me, this year is most memorable for what didn't happen--we did not get a full fledged hurricane rip through the Deepwater Horizon oil spill, nor did a devastating hurricane cause massive loss of life in Haiti's vulnerable earthquake zone. However, two hurricanes from this year are virtually certain to get their names retired--Tomas and Igor--and two other storms that did billions of damage to Mexico, Karl and Alex, are likely to have their names retired, as well.
The 19 named storms, 12 hurricanes, and 5 intense hurricanes were 198%, 203%, and 217% of the 1950-2000 average for named storms, hurricanes and major hurricanes, respectively. The nineteen named storms ties 2010 with 1995 and 1887 for 3rd place for most number of named storms in an Atlantic hurricane season. Only 2005 (28 named storms) and 1933 (21 named storms) were busier (Atlantic hurricane records go back to 1851, though there were likely many missed named storms prior to the beginning of satellite coverage in the mid-1960s.) This year also featured twelve hurricanes, tying 2010 with 1969 for second place for most hurricanes in a season. The record is held by 2005 with fifteen hurricanes. The five major hurricanes this year puts us in a tie for ninth place for most major hurricanes in a season. This year's Accumulated Cyclone Energy (ACE) index was 163, putting it in 13th place for ACE since 1944. A "hyperactive" hurricane season is considered to have an ACE index of >175% of the median. According to Wikipedia, median ACE measured over the period 1951–2000 for the Atlantic basin was 87.5, so 2010 is a hyperactive year by that definition (183% of the median.)
Friendly steering currents for the U.S.
As active as the 2010 season was, only one weak tropical storm made a direct landfall on the U.S. (Tropical Storm Bonnie, which hit South Florida in August as minimal tropical storm with 40 mph winds.) During the 15-year active hurricane period from 1995 - 2009, 33% of all named storms in the Atlantic hit the U.S., and 30% of all Atlantic hurricanes hit the U.S. at hurricane strength. Thus, the U.S. should have expected the landfall of six named storms, four of them being hurricanes, and two being intense hurricanes. So, the U.S. really lucked out this year. For comparison, here's how the U.S. fared in the four other hurricane seasons as busy or more busy:
2005: 28 storms, 7 hit the U.S. (5 were hurricanes, and 4 of those major hurricanes)
1933: 21 storms, 7 hit the U.S. (5 were hurricanes, and 3 of those were major hurricanes)
1995: 19 storms, 5 hit the U.S. (2 were hurricanes, and 1 was major)
1887: 19 storms, 5 hit the U.S. (3 were hurricanes, no majors)
We had twelve hurricanes in the Atlantic in 2010, yet none of them struck the U.S. Since 1900 there is no precedent of an Atlantic hurricane season with ten or more hurricanes where none has struck the U.S. as a hurricane. The eleven previous seasons with ten or more hurricanes--1870, 1878, 1886, 1893, 1916, 1933, 1950, 1969, 1995, 1998, and 2005--each had at least two hurricane strikes on the U.S. Since hurricane Ike (2008), there have been eighteen consecutive non US-landfalling hurricanes. Such a sequence last happened between Irene (1999) and Lili (2002), with 22 consecutive non US-landfalling hurricanes, and between Allen (1980) and Alicia (1983) with seventeen consecutive non US-landfalling hurricanes (thanks go to Adam Lea of tropicalstormrisk.com for these stats.)
No major Category 3 and stronger hurricanes have hit the U.S. since Hurricane Wilma of 2005. This is just the third such major hurricane drought since 1851. The other two such 5-year major hurricane droughts were 1901 - 1905 and 1910 - 1914. Also, 2010 is the only year besides 1951 when there have been five major hurricanes in the Atlantic, and none have hit the U.S. (1958 is also listed as such a year, but preliminary results from a re-analysis effort shows that Hurricane Helene hit North Carolina as a major hurricane that year.) There has never been a six year period without a U.S. major hurricane landfall.
The reason the U.S. got so lucky--and that Canada and Mexico took a much more severe beating than usual--was that the Azores/Bermuda high was farther east than usual, and there were more strong troughs of low pressure over the U.S. East Coast than usual. In addition, there was stronger high pressure than usual over the U.S. Gulf Coast, which deflected Caribbean storms into Mexico.
Intense hurricanes in unprecedented locations
Another remarkable feature of this year was that we saw three major hurricanes in rare or unprecedented locations. Julia was the easternmost major hurricane on record, Karl was the southernmost major hurricane on record in the Gulf of Mexico, and Earl was the 4th strongest hurricane so far north. This unusual major hurricane activity is likely due, in part, to the record tropical Atlantic sea surface temperatures this year. Sea surface temperatures in the tropical Atlantic from the Caribbean to the coast of Africa were at their warmest levels on record for almost the entire year.
Rare simultaneous hurricane occurrences and activity levels
On September 16, there were three simultaneous hurricanes--Karl, Igor, and Julia--in the Atlantic. According to Phil Klotzbach at Colorado State, three simultaneous Atlantic hurricanes is a rare phenomena, having occurred only eight other times since 1851. The other years were 1893, 1926, 1950, 1961, 1967, 1980, 1995, and 1998. Two of those years--1998 and 1893--had four simultaneous hurricanes.
Figure 2. Triple trouble: From left to right, Hurricanes Karl, Igor, and Julia roil the Atlantic. Image credit: NASA/GSFC.
On September 15, Hurricane Julia and Hurricane Igor were both Category 4 storms. This was just the second time in recorded history that two simultaneous Category 4 or stronger storms have occurred in the Atlantic. The only other occurrence was on 06 UTC September 16, 1926, when the Great Miami Hurricane and Hurricane Four were both Category 4 storms for a six-hour period. The were also two years, 1999 and 1958, when we missed having two simultaneous Category 4 hurricanes by six hours. The four Category 4 storms in 2010 makes this year tied for third place for most Category 4+ storms in a year. Only two other seasons have had as many as five Category 4 or stronger storms (2005 and 1999). This year is also holds the record for the earliest a fourth Category 4 or stronger storm has formed (though the fourth Category 4 of 1999, Hurricane Gert, formed just 3 hours later on September 15 in 1999.) We also had four Cat 4+ storms in just twenty days, which beat the previous record for shortest time span for four Cat 4+ storms to appear. The previous record was 1999--24 days. Eleven named storms formed between August 22 and September 29. This is the most named storms to form during this period, breaking the old record of nine named storms set in 1933, 1949, 1984 and 2002 (thanks go to Phil Klotzbach of CSU for the last two stats.)
Rare activity levels
Five hurricanes formed during the month of October. Only 1870 (six hurricanes) and 1950 (five hurricanes) have had five or more October hurricanes. We also had four Cat 4+ storms in just twenty days, which beat the previous record for shortest time span for four Cat 4+ storms to appear. The previous record was 1999--24 days. Eleven named storms formed between August 22 and September 29. This is the most named storms to form during this period, breaking the old record of nine named storms set in 1933, 1949, 1984 and 2002 (thanks go to Phil Klotzbach of CSU for the last two stats.)
Hurricane Alex had the highest sustained winds (100 mph) of any June hurricane since Hurricane Alma of 1966 (125 mph.)
As Hurricane Earl approached North Carolina on September 2, its 140 mph winds made it the fourth strongest Atlantic hurricane on record so far north. Only Hurricane Esther of 1961, Hurricane Connie of 1955, and Hurricane Two of 1922 had stronger winds at a more northerly latitude.
Figure 2. Hurricane Earl as seen from the International Space Station on Thursday, September 2, 2010. Image credit: NASA astronaut Douglas Wheelock.
Hurricane Igor: Newfoundland's worst hurricane in memory
Igor killed one person on Newfoundland, and damage exceeded $100 million, making Igor the most damaging tropical cyclone in Newfoundland history. A summary of the impact of Igor prepared by Environment Canada put it this way:
"Hurricane Igor and its severe impacts certainly represent a rare event in Newfoundland history which has been described as the worst in memory. In statistical terms, this was effectively a 50 - 100 year event depending on how one chooses to define it. There are no hurricanes/post tropical events of this magnitude striking Newfoundland in the modern era. Hurricane Juan in Nova Scotia was the last Atlantic Canadian hurricane to cause extreme damage. Prior to the naming of hurricanes, the 1935 Newfoundland Hurricane 75 years ago was of similar intensity."
Figure 3. A ravine carved by Hurricane Igor's flood waters washed out the Trans-Canada Highway, isolating Southeast Newfoundland from the rest of the province. Image credit: CBC News.
Hurricane Julia: strongest hurricane so far east
Hurricane Julia put on a remarkable and unexpected burst of intensification to become the season's fourth Category 4 storm. Julia's 135 mph winds made it the strongest hurricane on record so far east; the previous record was held by the eighth storm of 1926, which was only a 120 mph Category 3 hurricane at Julia's longitude. Julia's intensification was a surprise, since SSTs in the region were about 27.5°C, which is just 1°C above the threshold needed to sustain a Category 1 hurricane.
Hurricane Karl: strongest hurricane ever in the Bay of Campeche
Hurricane Karl was the first major hurricane on record in the Gulf of Mexico's Bay of Campeche--the region bounded by the Yucatan Peninsula on the east. There were two other major hurricanes that grazed the northern edge of the Bay of Campeche, Hurricane Hilda of 1955 and Hurricane Charley of 1951, but Karl is by far the farthest south a major hurricane has been in the Gulf of Mexico. Hurricane records go back to 1851, but Karl was a small storm and could have gotten missed as being a major hurricane before the age of aircraft reconnaissance (1945). Flooding from Karl caused an estimated $5.6 billion in damage to Mexico, making Karl this year's most damaging storm.
Figure 4. Tracks of all major hurricanes since 1851 near Mexico's Bay of Campeche. Karl is most southerly storm on record in the Gulf of Mexico. Image credit: NOAA Coastal Services Center.
Hurricane Paula sets a rapid intensification record
Hurricane Paula, the 16th named storm and 9th hurricane of the season, set a modern record for the fastest intensification from the issuance of the first advisory to hurricane strength. Paula reached hurricane strength just twelve hours after the first advisory was issued. Since reliable record keeping of intensification rates of Atlantic hurricanes began in 1970, when regular satellite coverage became available, no storm has ever intensified into a hurricane that quickly. Hurricane Humberto of 2007 held the previous record for fastest intensification from first advisory issued to hurricane strength--18 hours. However, there is one caveat to keep in mind. It is likely that when the final Atlantic hurricane data base (HURDAT) is constructed, Paula will be recognized as having been a tropical depression 3 - 9 hours before the first advisory was issued. Thus, it may turn out that Paula will be recognized as intensifying from first advisory to a hurricane in eighteen hours, tying Humberto's record. There have been six storms that accomplished the feat in 24 hours.
The formation of Tomas so far south and east so late in the season (October 29) is unprecedented in the historical record; no named storm has ever been present east of the Lesser Antilles (61.5°W) and south of 12°N latitude so late in the year. Hurricane Six of 1896 came close--it was also a tropical storm south of 12°N and east of 61.5°W on October 29, but nine hours earlier in the day. That storm recurved to the north and missed the Lesser Antilles. Tomas' track through the southern Lesser Antilles so late in the year is unprecedented. Another unusual aspect of Tomas' formation is that we had simultaneous hurricanes in the Atlantic Ocean on October 30--Tomas and Shary. There has been only one hurricane season since 1851 that had two simultaneous hurricanes later in the year--1932, when Hurricane Ten and Hurricane Eleven both existed November 7 - 10. Tomas was the 6th deadliest late-season Atlantic hurricane on record, and its preliminary death toll of 31 - 41 makes it the deadliest storm of the 2010 season. Tomas killed at least nine people and did at least $100 million in damage to St. Lucia, making it that island's second most damaging storm on record.
Figure 5. This landslide on St. Lucia after Tomas destroyed an art studio located just below the white car, killing several people. Image credit: Bernd Rac, Anse Chastanet.
Pre-season forecasts do well
Phil Klotzbach and Bill Gray of CSU have a more in-depth summary of this year's hurricane season. Kudos to them and all the other seasonal forecasting groups, whose forecasts of an exceptionally active Atlantic hurricane season were spot-on. CSU will make their first forecast for the 2011 hurricane season on Wednesday, December 12.