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Nineteen Atlantic tropical storms 3 consecutive years: a very rare event

The Atlantic Basin remains relatively quiet with no organized tropical features. We see no signs or support for tropical development for the next several days. So, the 2012 tropical season for the Atlantic will end on the quiet note.

The 2012 Atlantic hurricane season closes this Friday with another top-five tally for named storms--nineteen. This is the third consecutive year with nineteen named storms in the Atlantic, which is a remarkable level of activity for a three-year period. The closest comparable three-year period of activity occurred during 2003 - 2004 - 2005, when each season had fifteen-plus named storms. Since 1851, only two seasons--2005 (28 named storms) and 1933 (20 named storms)--have been busier than 2010, 2011, and 2012.


Figure 1. Preliminary tracks of the nineteen named storms from 2012. Image credit: National Hurricane Center.

How rare are 3 consecutive top-five hurricane seasons for named storms?
It is tremendously rare to get three consecutive top-five years in a database with a 162-year record. This would occur randomly just once every 34,000 years--assuming the database were unbiased, the climate were not changing, and a multi-year climate pattern favorable for active seasons were not present. However the database IS biased, the climate IS changing, and we have been in an active hurricane period that began in 1995. So, which of these factors may be responsible for recording three consecutive years with nineteen named storms? It is well-known that prior to the arrival of geostationary satellites in December 1966 and aircraft hurricane reconnaissance in 1945 that tropical storms in the Atlantic were under-counted. Landsea et al. (2004) theorized that we missed up to six named storms per year between 1851 - 1885, and up to four between 1886 - 1910. Landsea (2007) estimated the under-count to be 3.2 named storms per year between 1900 - 1965, and 1.0 per year between 1966 - 2002. Other studies have argued for lower under-counts. So, if we assume the highest under-counts estimated by Landsea et al. (2004) and Landsea (2007), here would be the top ten busiest Atlantic hurricane seasons since 1851:

2005: 28
1887: 25
1933: 23
1995: 20
2012, 2011, 2010, 1969, 1936: 19

So, 2012, 2011, and 2010 would still rank as top-five busiest seasons since 1851, but the odds of having three consecutive seasons with nineteen named storms would drop from a 1-in-34,000 year event to "only" a 1-in-5800 year event. More recently, Landsea et al. (2010) showed that the increasing trend in North Atlantic tropical storm frequency over the past 140 years was largely due to the increasing trend in short‐lived storms (storms lasting 2 days or less, called "shorties"), after the 1940s (Figure 2, top). They did not detect a significant increasing trend in medium‐ to long‐lived storms lasting more than 2 days. They wrote that "while it is possible that the recorded increase in short‐duration TCs [tropical cyclones] represents a real climate signal, we consider it is more plausible that the increase arises primarily from improvements in the quantity and quality of the observations, along with enhanced interpretation techniques." Villarini et al. (2011), in a paper titled, "Is the recorded increase in short-duration North Atlantic tropical storms spurious?", agreed. They attempted to correlate increases in tropical Atlantic sea surface temperatures in recent decades to the increase in short-lived Atlantic tropical storms, and were unable to do so. They wrote: using statistical methods combined with the current understanding of the physical processes, we are unable to find support for the hypothesis that the century‐scale record of short‐lived tropical cyclones in the Atlantic contains a detectable real climate signal. Therefore, we interpret the long‐term secular increase in short‐duration North Atlantic tropical storms as likely to be substantially inflated by observing system changes over time. These results strongly suggest that studies examining the frequency of North Atlantic tropical storms over the historical era (between the 19th century and present) should focus on storms of duration greater than about 2 days. So, let's do that. If we look during the past three hurricane seasons at how many "shorties" were observed, we see that a large number that stayed at tropical storm strength for two days or less: six storms in 2010, six in 2011, and seven in 2012. This leaves the hurricane seasons of 2010, 2011, and 2012 with twelve to thirteen tropical storms that lasted more than two days. This doesn't stand out that much when looking at trends since 1878 (Figure 2, bottom); there are now 25 years in the 135-year record with twelve or more long-lived tropical cyclones. However, there are no previous occurrences of three consecutive years with at least twelve long-lived tropical storms, so 2010, 2011, and 2012 still represent an unprecedented level of tropical storm activity in the historical record, and we would expect such an event to occur randomly about once every 157 years. That's a pretty rare event, and it is possible that climate change, combined with the fact we are in an active hurricane period that began in 1995, contributed to this rare event.


Figure 2. Atlantic tropical cyclones between 1878 - 2012 that spent two days or less at tropical storm strength (top) and more than two days at tropical storm strength or hurricane strength (bottom.) Figure updated from Villarini, G., G. A. Vecchi, T. R. Knutson, and J. A. Smith (2011), "Is the recorded increase in short-duration North Atlantic tropical storms spurious?", J. Geophys. Res., 116, D10114, doi:10.1029/2010JD015493.

References
Landsea, C. W., C. Anderson, N. Charles, G. Clark, J. Dunion, J. Fernandez‐Partagas, P. Hungerford, C. Neumann, and M. Zimmer (2004), "The Atlantic hurricane database re‐analysis project: Documentation for 1851-1910 alterations and additions to the HURDAT database," in Hurricanes and Typhoons ‐ Past, Present, and Future, edited by R. J. Murnane and K. B. Liu, pp. 178-221, Columbia Univ. Press, New York.

Landsea, C. W., (2007), "Counting Atlantic tropical cyclones back to 1900," Eos, 88(18), 197-202.

Villarini, G., G. A. Vecchi, T. R. Knutson, and J. A. Smith (2011), "Is the recorded increase in short-duration North Atlantic tropical storms spurious?", J. Geophys. Res., 116, D10114, doi:10.1029/2010JD015493

Jeff Masters

The bizarrely active hurricane season of 2012 draws to a close

The long and highly destructive hurricane season of 2012 has finally drawn to a close. The hurricane season of 2012 will long be remembered for spawning Hurricane Sandy--a freakish storm that was the largest, most powerful, and second most destructive Atlantic hurricane on record. But this year's hurricane season had a number of unique attributes, making it one of the most bizarre seasons I've witnessed. Despite featuring a remarkable nineteen named storms--tied for the third highest total since record keeping began in 1851--this year's hurricane season had just one major hurricane. That storm was Hurricane Michael, which stayed at Category 3 strength for a scant six hours. This is the least number of major hurricanes in a season since the El Ni�o year of 1997, which had only Category 3 Hurricane Erika. There were no Category 4 or 5 hurricanes in 2012, for just the 3rd time since the active hurricane period we are in began in 1995. The only two other years since 1995 without a Category 4 or stronger hurricane were the El Ni�o years of 2006 and 1997. Both of those seasons had around half the number of named storms of 2012--nine in 2006, and eight in 1997. The relative lack of strong storms in 2012 helped keep the Accumulated Cyclone Energy (ACE) down to 128, about 30% above average.


Figure 1. Hurricane Sandy at 10:10 am EDT October 28, 2012. Image credit: NASA/GSFC.

A near-average year for number of tropical cyclones hitting the U.S.
Since the active hurricane period we've been in began in 1995, the U.S. has averaged getting hit by 4 named storms per year, with an average of 1.7 of these being hurricanes, and 0.6 being major Category 3 and stronger hurricanes. This year, we were hit by 3 named storms (Beryl, Debby, and Isaac). One of these was a hurricane (Isaac). Sandy didn't count as a hurricane strike on the U.S., since it transitioned to an extratropical cyclone a few hours before landfall. No major hurricanes hit the U.S., making 2012 the 7th consecutive year without a major hurricane strike. The only other time we've had a streak that long occurred between 1861 - 1868, during the decade of the Civil War.


Figure 2. Vertical instability over the tropical Atlantic in 2004 - 2012 (blue line) compared to average (black line.) The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere (note that the same scale is not used in all the plots, making the black climatological line appear different, when it is really the same for each plot.) Thunderstorms grow much more readily when vertical instability is high. Instability was near average during the August - October peak of hurricane season in 2004 - 2009, but was much lower than average during the hurricane seasons of 2010 - 2012. There was an unusual amount of dry, sinking air in the tropical Atlantic during 2010 - 2012, and the resulting low atmospheric instability reduced the proportion of tropical storms that have intensified into hurricanes. Vertical instability from 2004 - 2011 is taken from NOAA/RAMMB and for 2012 from NOAA/SSD.

Unusually stable air over the Tropical Atlantic in 2012
For the third consecutive hurricane season, 2012 featured an unusual amount of dry, sinking air over the tropical Atlantic and Caribbean Sea. Due to warmer-than-average sea surface temperatures and an active African Monsoon that generated plenty of African waves, a remarkably high number of tropical storms managed to form, but the unusually stable air in the hurricane genesis regions made it difficult for the storms to become strong. When we did see storms undergo significant intensification, it tended to occur outside of the tropics, north of 25°N, where there was not as much dry, sinking air (Sandy's intensification as it approached landfall in Cuba was an exception to this rule.) If we look at the last nine hurricane seasons (Figure 2), we can see that the hurricane seasons of 2010, 2011, and 2012 all featured similar levels of highly stable air over the tropical Atlantic. This is in marked contrast to what occurred the previous six years. The past three seasons all featured a near-record number of named storms (nineteen each year), but an unusually low ratio of strong hurricanes. Steering patterns the past three years also acted to keep most of the storms out to sea. Is this strange pattern something we'll see more of, due to climate change? Or is it mostly due to natural cycles in hurricane activity? I don't have any answers at this point, but the past three hurricane seasons have definitely been highly unusual in a historical context. I expect the steering currents to shift and bring more landfalling hurricanes to the U.S. at some point this decade, though.


Figure 3. Sea water floods the Ground Zero construction site at the World Trade Center, Monday, Oct. 29, 2012, in New York City. Image credit: AP.

Most notable events of the Hurricane Season of 2012
Hurricane Sandy was truly astounding in its size and power. At its peak size, twenty hours before landfall, Sandy had tropical storm-force winds that covered an area nearly one-fifth the area of the contiguous United States. Since detailed records of hurricane size began in 1988, only one tropical storm (Olga of 2001) has had a larger area of tropical storm-force winds, and no hurricanes has. Sandy's area of ocean with twelve-foot seas peaked at 1.4 million square miles--nearly one-half the area of the contiguous United States, or 1% of Earth's total ocean area. Most incredibly, ten hours before landfall (9:30 am EDT October 30), the total energy of Sandy's winds of tropical storm-force and higher peaked at 329 terajoules--the highest value for any Atlantic hurricane since at least 1969. This is 2.7 times higher than Katrina's peak energy, and is equivalent to five Hiroshima-sized atomic bombs. At landfall, Sandy's tropical storm-force winds spanned 943 miles of the the U.S. coast. No hurricane on record has been wider; the previous record holder was Hurricane Igor of 2010, which was 863 miles in diameter. Sandy's huge size prompted high wind warnings to be posted from Chicago to Eastern Maine, and from Michigan's Upper Peninsula to Florida's Lake Okeechobee--an area home to 120 million people. Sandy's winds simultaneously caused damage to buildings on the shores of Lake Michigan at Indiana Dunes National Lake Shore, and toppled power lines in Nova Scotia, Canada--locations 1200 miles apart!


Figure 4. Hurricane Isaac lit up by moonlight as it spins towards the city of New Orleans, LA, on August 26, 2012. The Suomi National Polar-orbiting Partnership (NPP) satellite captured these images with its Visible Infrared Imaging Radiometer Suite (VIIRS). The "day-night band" of VIIRS detects light in a range of wavelengths from green to near-infrared and uses light intensification to enable the detection of dim signals. Image Credit: NASA/NOAA, Earth Observatory.

Hurricane Isaac hit Louisiana as a Category 1 hurricane with 80 mph winds on August 28, but the storm's massive wind field brought a storm surge characteristic of a Category 2 hurricane to the coast. A storm surge of 11.1 feet was measured at Shell Beach, LA and higher surges were reported in portions of Louisiana. Fortunately, the new $14.5 billion upgrade to the New Orleans levee system kept the city dry. Isaac killed 9 people in the U.S., and 29 in the Caribbean.

Hurricane Ernesto hit Mexico's Yucatan Peninsula as a Category 1 hurricane with 85 mph winds on August 7. The storm killed 12 and did at least $250 million in damage.

Tropical Storm Debby formed on June 23, the earliest formation date on record for the season's 4th storm. The previous record was Dennis, on July 5, 2005. Debby killed seven and did over $300 million in damage, but helped relieve drought conditions over Northern Florida and Southern Georgia.

Tropical Storm Beryl, which made landfall on May 28 near Jacksonville Beach, FL with 70 mph winds, was the strongest tropical storm to make landfall in the U.S. prior to June 1. Beryl killed two but did minimal damage.

Nadine lasted for 21.75 days as a named storm, the 5th longest-lasting tropical storm in the Atlantic basin.

It was the 3rd year in a row with 19 named storms.

No named storms existed during the month of July and November, but we still managed big numbers.

Only 7 seasons have had more hurricanes than 2012.

The season had two named storm before the official June 1 start of hurricane season, only the 3rd time that has occurred.

Eight named storms formed in August, which tied 2004 for the most to form in that month.

The Colorado State University hurricane forecast team, led by Phil Klotzbach and Bill Gray, has a more in-depth summary of the 2012 hurricane season.

Jeff Masters

Conclusion of 2012 Hurricane Season

Today, Friday, November 30, marks the conclusion of the 2012 hurricane season. It was a season that saw well above average activity.

During this year's season, there were 19 named systems. Of these, nine were tropical storms. Ten systems became hurricanes and one attained major hurricane status. Hurricane Michael was the only major hurricane of the season, with maximum wind speed of 115 miles per hour.

In a typical season based on the period covering the years 1950 to 2000, there would be on average 9 to 10 named storms, 6 hurricanes and 2 to 3 major hurricanes of category 3, 4 or 5. Conditions such as the El Ni�o phenomenon which was to have a suppressing effect on this year's tropical cyclone activity did not evolve as timely as predicted - hence the above average tropical cyclone activity this year.

Here at home, Belize had a close call with Hurricane Ernesto. This hurricane, with maximum sustained winds of 85 miles per hour, made landfall just south of Mahahual, Quintana Roo, Mexico at about 9:15 p.m. on Tuesday, August 7. The track of Hurricane Ernesto focused the likely impacts mainly on the Corozal and Orange Walk Districts.

However, impacts to infrastructure were negligible, with the agricultural sector suffering some losses. Ernesto not only turned out to be largely an inconvenience, but also set the stage for a major flooding event that was to follow in the following six days or so in the Corozal District, particularly in the town itself.

Citizens are advised to review their preparedness plans in order to identify those parts that did not function properly this past 2012 season, with an aim to improving on those failures and weaknesses. This would lead to enhanced safety and preparedness for the 2013 season.

We at the National Meteorological Service will continue to work diligently to improve on our products and services during this off season, so as to be better able to provide even more timely and accurate tropical cyclone forecasts in addition to the other routine services provided daily.

Amandala

"Well Above-Average" hurricane season puts Belize to the test

The 2012 Atlantic Hurricane Season which includes the North Atlantic, Caribbean Sea and Gulf of Mexico area came to an end on November 30th. The 2012 hurricane season saw 19 named systems, one of which put Belize's emergency plan to a test. This occurred when hurricane Ernesto made landfall south of Mahahual in the state of Quintana Roo Mexico on the 27th August at about 9:15PM. The 2012 season was considered to have been well above-average and differed from what was projected at the start of the season.

The hurricane season, which begins on June 1st and ends on the 30th of November, did not bring any hurricane systems directly to Belize. Chief Meteorologist Dennis Gonguez of the Belize Meteorological Service outlined the season, looking back at the activities in the Atlantic area. "This past 2012 hurricane season was rather active. We saw well above average tropical cyclone activities. During this year there were 19 named systems and in a typical year you would have about nine to ten so we saw almost twice as many systems this year. Of the 19 named systems, ten became hurricanes and in a typical year we would have about six hurricanes; again it shows that the activities were well above normal. Of the ten hurricanes, one became a major hurricane (Hurricane Michael - Cat 3). So this year's activities were well above normal".

He also added that the forecast did not stand out as projected, as there were more named storms than there were intense systems, stating that "the suppressing phenomenon" which the forecasters had expected did not develop as strongly and as timely as projected. "The El Ni�o phenomenon, which normally has a dampening affect on our hurricane season did not evolve as strongly as we had expected, so we did not have that increase in storm intensity this year," said Gonguez.

Meanwhile Belize was spared a major blow from the forces of 85-mile per hour Hurricane Ernesto, the only storm that came near to Belize. The rains of Ernesto however, combined with a tropical wave a week after, left major portions of northern Belize under water. "Hurricane Ernesto did produce significant rain fall. However it was the tropical wave that passed a week or so later that caused major flooding in the northern part of the country, which was the major occurrence for the country during the 2012 hurricane season," said Gonguez.

"Even though we kind of dodged the bullet with hurricane Ernesto, we should not be too complacent. In a busy year we may not see a system, however in a quiet year you can get hit by one single system which could disrupt your country for the next five or six years. So the forecast may tell how active the season may be, but it does not tell where the systems will make landfall," advised Gonguez, who further stated that Belize was tested and that the country's forecast and emergency plan was well prepared when tested by Ernesto.

Meteorologist Gonguez ended by advising Belizeans to take the other six months and do a post mortem of their personal and family emergency plan. "Let's see where the plan failed, especially when they were tested during hurricane Ernesto, and let's sort out and look and see how we can improve on those failures and weaknesses in our emergency plan," added Gonguez.

A few important fact about the the 2012 Atlantic hurricane season is that it tied with 1887, 1995, 2010, and 2011 Atlantic Hurricane season and is the third most active year in recorded history. In addition over half of the tropical cyclones that developed in the season made landfall or directly impacted land. Two hurricanes, Sandy and Isaac, were the deadliest and most destructive. Sandy caused at least US$65.5 billion in damage and is the second costliest hurricane in recorded history (the costliest being Hurricane Katrina). It caused 253 deaths over the seven countries in its path. Isaac caused an estimated US$2.3 billion and 41 deaths. Closer to Belize, Ernesto was a long-tracked Category 1 hurricane that ultimately made landfall north of Belize in southern Mexico, causing a total of 12 deaths and producing damages totaling US$252.2 million. The combined storms during the entire season killed at least 320 people and caused at least US$68 billion in damages, making it the deadliest season since 2008, and the costliest since 2005.

Click here to read the rest of the article and see more photos in the San Pedro Sun