Hurricane Epsilon
Encyclopedia
Hurricane Epsilon was a long-lasting hurricane
of the 2005 Atlantic hurricane season
in late November and early December. It was the 27th of 28 tropical or subtropical cyclone
s, as well as the last of 15 hurricanes of the record-breaking year. Originating from a cold front
beneath an upper-level low, Epsilon formed on November 29 about 915 mi (1470 km) east of Bermuda. Initially, the National Hurricane Center
(NHC) forecast the storm to transition into an extratropical cyclone
within five days, due to conditions unfavorable for significant intensification. Epsilon continually defied forecasts, at first due to an unexpected loop to the southwest, and later due to retaining its strength despite cold waters and strong wind shear.
On December 1, Epsilon began a northeast motion due to an approaching trough, and the next day it attained hurricane status. After turning to the east, it developed characteristics of an annular hurricane
, meaning it had a circular eye, a ring of convection, and had little fluctuations in its intensity. On December 5 Epsilon attained peak winds of 85 mph (140 km/h), and the next day it turned to the south and southwest. Late on December 7, the winds dropped below hurricane status for the first time in five days, making Epsilon the longest-lasting December hurricane. Stronger wind shear caused rapid weakening, and the storm could no longer be classified as a tropical cyclone late on December 8. The next day the remnant circulation of Epsilon dissipated.
-force winds developed beneath an upper-level
low pressure area
, about 1150 mi (1850 km) east of Bermuda
. At the time, a cold front
extended eastward from the surface storm toward the eastern Atlantic Ocean, north of Tropical Storm Delta
. By that time, tropical cyclone forecast models anticipated the possible development of a subtropical cyclone
, and although they were inconsistent, National Hurricane Center
(NHC) specialist Eric Blake stated, "blocking at high latitudes seems to favor another subtropical cyclone effort." The blocking referred to a ridge
stretching across the northern Atlantic. The surface storm gradually separated from the frontal zone, but initially its convection, or thunderstorm activity, was sparse and poorly-organized.
The NHC introduced the system in its tropical weather outlook on November 28, with the possibility of subtropical or tropical development
noted. It moved slowly westward, becoming better organized, and by late that day resembled a subtropical cyclone; however, as it was still connected to the cold front, it could not have been classified as such. Early on November 29, an area of deep convection developed and organized over the surface center when it was about 915 mi (1470 km) east of Bermuda. The NHC accordingly assessed the system as developing into a tropical storm, designating it with the Greek letter
Epsilon
.
on November 28, about nine hours after it actually developed. By that time, the convection had wrapped into a ring 45 mi (72.4 km) in diameter. In the first advisory on Epsilon, the NHC forecast steady strengthening to near hurricane status due to marginally favorable conditions, followed by extratropical
transition within five days; an alternate possibility was Epsilon being absorbed by a larger extratropical storm. The storm moved westward after its development with a persistent ridge to its north. Initially, Epsilon was embedded beneath an upper-level low that provided an area of low wind shear
and instability. An eye-like
feature briefly developed in the center of the convection, although the thunderstorms waned late on November 28 due to restricted inflow
. However, banding features and outflow
improved at the same time.
By November 30, the NHC anticipated extratropical transition to occur within two days, although some strengthening was still expected. That day, there was an increase in convection over the center and the development of a ragged eye-feature. The winds briefly increased to 65 mph (104.6 km/h), although the intensity of the thunderstorms diminished. Initially Epsilon was predicted to continue westward and eventually turn to the north and northeast. Instead, it turned toward the southwest and executed a cyclonic loop; the unexpected motion caused larger than normal errors in the extended track forecast. As it moved to the south, the storm crossed over an area of warmer water temperatures, and the NHC remarked that "just a modest increase in convection [would be] needed to make Epsilon a hurricane." At the time, forecasters assessed the winds in Epsilon to be around 70 mph (112.7 km/h), although in a post-season re-analysis it was found to have been 10 mph (16.1 km/h) weaker. Late on November 30, Epsilon made its closest approach to Bermuda, passing about 645 miles (1045 km) east-southeast of the island.
Tropical Storm Epsilon began its motion to the east and northeast on December 1, due to an approaching trough. Its structure became that of a "shallow hybrid-type tropical cyclone", and an eye-feature again developed within the convection. At the time, the NHC and several computer models anticipated extratropical transition within 36 hours as it accelerated northeastward near the Azores. However, four computer models predicted an alternate scenario, and forecaster Stacy Stewart stated such transition would only occur "barring any southward motion over warmer water that would prolong both the lifetime of Epsilon and the 2005 Atlantic hurricane season." As it continued northeastward, the storm separated from upper-level low it was previously beneath. After a decrease in convection, the thunderstorm activity again increased over the center, and there were more banding features. Despite moving over slightly cooler water temperatures, Epsilon attained hurricane status late on December 2, following the development of a well-defined eye 29 miles (46 km) in diameter.
A few hours after reaching hurricane status, the NHC thought Epsilon reached peak winds, as the storm was about to move over cooler water temperatures. Additionally, the hurricane was expected to stall near the Azores, in contrast to the original forecast of continued acceleration to the northeast. On December 3 it turned due eastward, still maintaining an eye, modest amounts of convection, and outflow. Despite moving into an area of cooler waters and generally unfavorable atmospheric conditions, Epsilon retained its hurricane status; the only entity supporting its intensity was its warm upper-level temperature. By late on December 3, its presentation was described as "remarkably well-organized for a hurricane at high latitude in December... embedded in a strong upper-level westerly wind environment and moving over [70–72 °F (21–22 °C)] water."
As it continued eastward, Epsilon developed characteristics of an annular hurricane
; such cyclones, more often found in the deep tropics with greater intensity, have circular eyes, surrounded by a nearly uniform ring of convection and a general lack of thunderstorms outside the ring. For several days, the intensity fluctuated in a narrow range, and although Epsilon was briefly downgraded to tropical storm status on December 4, the NHC assessed it as remaining a hurricane. After it was thought to have weakened, the eye became more symmetric as the ring of convection became stronger. The hurricane remained difficult to forecast, as NHC forecaster Lixion Avila remarked, "There are no clear reasons... and I am not going to make one up... to explain the recent strengthening of Epsilon."
By late on December 4, the NHC was no longer anticipating extratropical transition, after a front passed north of the storm and there was no interaction. At 0600 UTC on December 5, the hurricane's appearance generated 4.7 on the Dvorak technique
, a system used to estimate intensity from satellite imagery. This was the highest rating during Epsilon's duration, and suggested winds of 85 mph (140 km/h), which was its peak intensity. Around that time, the hurricane began a turn to the east-southeast, as the ridge to its north built behind the passage of a cold front. Despite the cold water temperatures and unfavorable strong upper-level winds, Epsilon maintained its intensity, and the Geophysical Fluid Dynamics Laboratory
(GFDL) model predicted it would remain a hurricane for nearly three days.
Once weakened to a tropical storm, Epsilon began rapidly deteriorating. On December 8, it was downgraded to a tropical depression as the convection had totally dissipated. The NHC issued their final advisory on Epsilon at 1500 UTC that day, after the cyclone consisted of a tight swirl of low clouds with no convection. On issuing the last advisory, Lixion Avila remarked, "I hope this is the end of the long lasting 2005 hurricane season." There was ultimately one more tropical storm – Zeta
.
Late on December 8, Epsilon transitioned into a remnant low pressure area. The remnant circulation elongated in advance of a frontal zone, and it dissipated late on December 9. The front absorbed the remnants the next day.
After completing the list of 21 tropical cyclone names for the first time ever, the NHC began naming storms with the Greek alphabet. Epsilon was the fifth name of the list, and ultimately there was one additional storm, making the 2005 season the most active on record with 27 named storms. Since Epsilon stayed well out to sea and never approached land, no warnings or watches
were issued. No ships reported tropical storm force winds from Epsilon and there were no damages or fatalities.
When Tropical Storm Epsilon persisted until December 1, it extended the 2005 Atlantic hurricane season beyond the normal boundaries of June 1 to November 30. Although such off-season Atlantic storms are unusual, a similar event occurred just one year prior with Tropical Storm Otto.
Epsilon is just one of four tropical cyclones to ever attain hurricane status in December, along with a hurricane in 1887
, Alice in 1954, and Lili
in 1984. The cyclone maintained hurricane status for five days, longer than any other Atlantic hurricane in December.
NHC's archive on Hurricane Epsilon
`
Tropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
of the 2005 Atlantic hurricane season
2005 Atlantic hurricane season
The 2005 Atlantic hurricane season was the most active Atlantic hurricane season in recorded history, repeatedly shattering numerous records. The impact of the season was widespread and ruinous with an estimated 3,913 deaths and record damage of about $159.2 billion...
in late November and early December. It was the 27th of 28 tropical or subtropical cyclone
Subtropical cyclone
A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical or extratropical cyclones. They were officially recognized by the National...
s, as well as the last of 15 hurricanes of the record-breaking year. Originating from a cold front
Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...
beneath an upper-level low, Epsilon formed on November 29 about 915 mi (1470 km) east of Bermuda. Initially, the National Hurricane Center
National Hurricane Center
The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...
(NHC) forecast the storm to transition into an extratropical cyclone
Extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...
within five days, due to conditions unfavorable for significant intensification. Epsilon continually defied forecasts, at first due to an unexpected loop to the southwest, and later due to retaining its strength despite cold waters and strong wind shear.
On December 1, Epsilon began a northeast motion due to an approaching trough, and the next day it attained hurricane status. After turning to the east, it developed characteristics of an annular hurricane
Annular hurricane
An annular hurricane, also known as a truck tire or doughnut hurricane, is a tropical cyclone in the Atlantic or Eastern Pacific Oceans that features a large, symmetric eye surrounded by a thick ring of intense convection. This type of storm is not prone to the fluctuations in intensity associated...
, meaning it had a circular eye, a ring of convection, and had little fluctuations in its intensity. On December 5 Epsilon attained peak winds of 85 mph (140 km/h), and the next day it turned to the south and southwest. Late on December 7, the winds dropped below hurricane status for the first time in five days, making Epsilon the longest-lasting December hurricane. Stronger wind shear caused rapid weakening, and the storm could no longer be classified as a tropical cyclone late on December 8. The next day the remnant circulation of Epsilon dissipated.
Formation and naming
On November 27, a surface storm with galeGale
A gale is a very strong wind. There are conflicting definitions of how strong a wind must be to be considered a gale. The U.S. government's National Weather Service defines a gale as 34–47 knots of sustained surface winds. Forecasters typically issue gale warnings when winds of this strength are...
-force winds developed beneath an upper-level
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....
low pressure area
Low pressure area
A low-pressure area, or "low", is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence which occur in upper levels of the troposphere. The formation process of a low-pressure area is known as...
, about 1150 mi (1850 km) east of Bermuda
Bermuda
Bermuda is a British overseas territory in the North Atlantic Ocean. Located off the east coast of the United States, its nearest landmass is Cape Hatteras, North Carolina, about to the west-northwest. It is about south of Halifax, Nova Scotia, Canada, and northeast of Miami, Florida...
. At the time, a cold front
Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...
extended eastward from the surface storm toward the eastern Atlantic Ocean, north of Tropical Storm Delta
Tropical Storm Delta (2005)
TropicalStorm Delta was a late-forming tropical storm of the 2005 Atlantic hurricane season which struck the Canary Islands as a strong extratropical storm, causing significant damage and then crossed over Morocco before dissipating...
. By that time, tropical cyclone forecast models anticipated the possible development of a subtropical cyclone
Subtropical cyclone
A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical or extratropical cyclones. They were officially recognized by the National...
, and although they were inconsistent, National Hurricane Center
National Hurricane Center
The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...
(NHC) specialist Eric Blake stated, "blocking at high latitudes seems to favor another subtropical cyclone effort." The blocking referred to a ridge
Ridge (meteorology)
A ridge is an elongated region of relatively high atmospheric pressure, the opposite of a trough....
stretching across the northern Atlantic. The surface storm gradually separated from the frontal zone, but initially its convection, or thunderstorm activity, was sparse and poorly-organized.
The NHC introduced the system in its tropical weather outlook on November 28, with the possibility of subtropical or tropical development
Tropical cyclogenesis
Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...
noted. It moved slowly westward, becoming better organized, and by late that day resembled a subtropical cyclone; however, as it was still connected to the cold front, it could not have been classified as such. Early on November 29, an area of deep convection developed and organized over the surface center when it was about 915 mi (1470 km) east of Bermuda. The NHC accordingly assessed the system as developing into a tropical storm, designating it with the Greek letter
Greek alphabet
The Greek alphabet is the script that has been used to write the Greek language since at least 730 BC . The alphabet in its classical and modern form consists of 24 letters ordered in sequence from alpha to omega...
Epsilon
Epsilon
Epsilon is the fifth letter of the Greek alphabet, corresponding phonetically to a close-mid front unrounded vowel . In the system of Greek numerals it has a value of 5. It was derived from the Phoenician letter He...
.
Tropical storm intensity
Operationally, the NHC did not initiate advisories until 1500 UTCCoordinated Universal Time
Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...
on November 28, about nine hours after it actually developed. By that time, the convection had wrapped into a ring 45 mi (72.4 km) in diameter. In the first advisory on Epsilon, the NHC forecast steady strengthening to near hurricane status due to marginally favorable conditions, followed by extratropical
Extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...
transition within five days; an alternate possibility was Epsilon being absorbed by a larger extratropical storm. The storm moved westward after its development with a persistent ridge to its north. Initially, Epsilon was embedded beneath an upper-level low that provided an area of low wind shear
Wind shear
Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...
and instability. An eye-like
Eye (cyclone)
The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the second most severe weather of a cyclone...
feature briefly developed in the center of the convection, although the thunderstorms waned late on November 28 due to restricted inflow
Inflow (meteorology)
Inflow is the flow of a fluid into a large collection of that fluid. Within meteorology, inflow normally refers to the influx of warmth and moisture from air within the Earth's atmosphere into storm systems. Extratropical cyclones are fed by inflow focused along their cold front and warm fronts...
. However, banding features and outflow
Outflow (meteorology)
Outflow, in meteorology, is air that flows outwards from a storm system. It is associated with ridging, or anticyclonic flow. In the low levels of the troposphere, outflow radiates from thunderstorms in the form of a wedge of rain-cooled air, which is visible as a thin rope-like cloud on weather...
improved at the same time.
By November 30, the NHC anticipated extratropical transition to occur within two days, although some strengthening was still expected. That day, there was an increase in convection over the center and the development of a ragged eye-feature. The winds briefly increased to 65 mph (104.6 km/h), although the intensity of the thunderstorms diminished. Initially Epsilon was predicted to continue westward and eventually turn to the north and northeast. Instead, it turned toward the southwest and executed a cyclonic loop; the unexpected motion caused larger than normal errors in the extended track forecast. As it moved to the south, the storm crossed over an area of warmer water temperatures, and the NHC remarked that "just a modest increase in convection [would be] needed to make Epsilon a hurricane." At the time, forecasters assessed the winds in Epsilon to be around 70 mph (112.7 km/h), although in a post-season re-analysis it was found to have been 10 mph (16.1 km/h) weaker. Late on November 30, Epsilon made its closest approach to Bermuda, passing about 645 miles (1045 km) east-southeast of the island.
Tropical Storm Epsilon began its motion to the east and northeast on December 1, due to an approaching trough. Its structure became that of a "shallow hybrid-type tropical cyclone", and an eye-feature again developed within the convection. At the time, the NHC and several computer models anticipated extratropical transition within 36 hours as it accelerated northeastward near the Azores. However, four computer models predicted an alternate scenario, and forecaster Stacy Stewart stated such transition would only occur "barring any southward motion over warmer water that would prolong both the lifetime of Epsilon and the 2005 Atlantic hurricane season." As it continued northeastward, the storm separated from upper-level low it was previously beneath. After a decrease in convection, the thunderstorm activity again increased over the center, and there were more banding features. Despite moving over slightly cooler water temperatures, Epsilon attained hurricane status late on December 2, following the development of a well-defined eye 29 miles (46 km) in diameter.
Peak strength and hurricane status
As it continued eastward, Epsilon developed characteristics of an annular hurricane
Annular hurricane
An annular hurricane, also known as a truck tire or doughnut hurricane, is a tropical cyclone in the Atlantic or Eastern Pacific Oceans that features a large, symmetric eye surrounded by a thick ring of intense convection. This type of storm is not prone to the fluctuations in intensity associated...
; such cyclones, more often found in the deep tropics with greater intensity, have circular eyes, surrounded by a nearly uniform ring of convection and a general lack of thunderstorms outside the ring. For several days, the intensity fluctuated in a narrow range, and although Epsilon was briefly downgraded to tropical storm status on December 4, the NHC assessed it as remaining a hurricane. After it was thought to have weakened, the eye became more symmetric as the ring of convection became stronger. The hurricane remained difficult to forecast, as NHC forecaster Lixion Avila remarked, "There are no clear reasons... and I am not going to make one up... to explain the recent strengthening of Epsilon."
By late on December 4, the NHC was no longer anticipating extratropical transition, after a front passed north of the storm and there was no interaction. At 0600 UTC on December 5, the hurricane's appearance generated 4.7 on the Dvorak technique
Dvorak technique
The Dvorak technique is a widely used system to subjectively estimate tropical cyclone intensity based solely on visible and infrared satellite images. Several agencies issue Dvorak intensity numbers for cyclones of sufficient intensity...
, a system used to estimate intensity from satellite imagery. This was the highest rating during Epsilon's duration, and suggested winds of 85 mph (140 km/h), which was its peak intensity. Around that time, the hurricane began a turn to the east-southeast, as the ridge to its north built behind the passage of a cold front. Despite the cold water temperatures and unfavorable strong upper-level winds, Epsilon maintained its intensity, and the Geophysical Fluid Dynamics Laboratory
Geophysical Fluid Dynamics Laboratory
The Geophysical Fluid Dynamics Laboratory is a laboratory in the National Oceanic and Atmospheric Administration /Office of Oceanic and Atmospheric Research . The current director is Dr. V...
(GFDL) model predicted it would remain a hurricane for nearly three days.
Weakening and dissipation
On December 6 the hurricane turned to the south and southwest. As it did so, Epsilon passed beneath a mid-level trough that sheltered it from the wind shear. After weakening during the evening, the convection redeveloped around the large and distinct eye in the daytime, a process Epsilon had done repeatedly in its duration. However, late on December 7, an approaching trough began increasing wind shear over the system, displacing the convection from the center and causing the eye to dissipate. After maintaining hurricane status for five days, Epsilon weakened to tropical storm status about 920 mi (1480 km) southwest of the Azores.Once weakened to a tropical storm, Epsilon began rapidly deteriorating. On December 8, it was downgraded to a tropical depression as the convection had totally dissipated. The NHC issued their final advisory on Epsilon at 1500 UTC that day, after the cyclone consisted of a tight swirl of low clouds with no convection. On issuing the last advisory, Lixion Avila remarked, "I hope this is the end of the long lasting 2005 hurricane season." There was ultimately one more tropical storm – Zeta
Tropical Storm Zeta (2005)
Tropical Storm Zeta was a late-developing tropical storm over the central Atlantic which formed after the 2005 Atlantic hurricane season had officially ended , and continued into January 2006...
.
Late on December 8, Epsilon transitioned into a remnant low pressure area. The remnant circulation elongated in advance of a frontal zone, and it dissipated late on December 9. The front absorbed the remnants the next day.
Naming and records
Tropical cyclone warnings and watches
Warnings and watches are two levels of alert issued by national weather forecasting bodies to coastal areas threatened by the imminent approach of a tropical cyclone of tropical storm or hurricane intensity. They are notices to the local population and civil authorities to make appropriate...
were issued. No ships reported tropical storm force winds from Epsilon and there were no damages or fatalities.
When Tropical Storm Epsilon persisted until December 1, it extended the 2005 Atlantic hurricane season beyond the normal boundaries of June 1 to November 30. Although such off-season Atlantic storms are unusual, a similar event occurred just one year prior with Tropical Storm Otto.
Epsilon is just one of four tropical cyclones to ever attain hurricane status in December, along with a hurricane in 1887
1887 Atlantic hurricane season
Another May storm formed south of Jamaica on May 17, way outside of the season and moved generally northward. It crossed Cuba on the 19th as a tropical storm, and moved out to sea. Two peaked at twice, once on May 18 and May 20. Two dissipated on the 21st in the Atlantic Ocean...
, Alice in 1954, and Lili
Hurricane Lili (1984)
Hurricane Lili was one of only five Atlantic tropical cyclones on record to reach hurricane status in the month of December. The final of thirteen tropical storms in the 1984 Atlantic hurricane season, Lili developed as a subtropical cyclone which originated from a frontal trough to the south of...
in 1984. The cyclone maintained hurricane status for five days, longer than any other Atlantic hurricane in December.
External links
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