Jason Harris
EF5
I'm sure someone can find a better source for annular hurricanes, but the "gov" sources all seem to assume a definition rather than state one clearly, so here's something from wikipedia, and although one must be skeptical of wikipedia this does sound like it came from someone well-versed in the subject:
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Annular hurricane
Wikipedia, the free encyclopedia - Cite This Source
An annular 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 with eyewall replacement cycles, unlike typical intense tropical cyclones. Annular hurricanes also tend to persist, even when encountering environmental conditions which easily dissipate most other hurricanes. Forecasters have difficulty predicting the behavior of annular hurricanes; they are a recently recognized phenomenon, and as such, little is known about their tendencies. Because of this, they can be more dangerous than typical hurricanes.
Characteristics
Annular hurricanes are axisymmetric — symmetric along every radial axis, i.e. very circular in appearance. They lack the spiralform rainbands which are characteristic of typical tropical cyclones. After reaching peak intensity, they weaken much more slowly than non-annular storms of similar intensity. However, most annular hurricanes have annular characteristics for only a portion of their lifetimes.
While hurricanes retain annular characteristics, they also seem to be less affected by diurnal, or daily variations. Most annular hurricanes have peak intensities of greater than 85 knots (100 mph, 155 km/h) and more than 85% of their theoretical maximum potential intensity.
Annular hurricanes maintain their intensities longer than usual after their peaks. Statistics show that forecasters significantly overestimate the lessening of wind velocities in annular hurricanes. In terms of the Dvorak technique, annular hurricanes weaken very slowly after their peak (on average, less than 0.5 T after one day from their peak intensities).
Annular hurricanes are very rare. Few storms meet all of the criteria, although many strong storms resemble annular hurricanes in some criteria. Fewer than 1% of Atlantic tropical cyclones encounter all of the environmental conditions associated with annular hurricanes. In the Eastern Pacific, such conditions are more common, but still very unusual — 3% of Pacific tropical cyclones encounter them.
An algorithm for objective identification, in real time, of annular hurricanes has been developed and shows skill, but it is not yet operational.
Formation
Research into the characteristics and formation of annular hurricanes is still in its infancy. First classified and categorized in 2002, little is known about how they form, or why some are able to maintain their intensity in hostile conditions.
What meteorologists do know is that a normal hurricane, after undergoing an eyewall replacement cycle, fails to re-establish the standard hurricane appearance. The new eyewall thickens, and rainbands dissipate, and the hurricane takes on an annular structure. As compared to the formation of normal hurricanes, this happens under weaker wind shear and, surprisingly, cooler sea surface temperatures.
Some of the conditions associated with annular hurricanes are:
* An intensity 85% or greater from their theoretical maximum potential intensity,
* Weak wind shear from the east or southeast,
* A cold east wind at a high altitude (the 200 mbar pressure level),
* Near-constant sea surface temperatures between 25.4 °C and 28.5 °C, and
* Lack of relative eddy flux convergence at the 200 mbar pressure level, relative to the storm.
Notable annular hurricanes
Hurricane Luis of the 1995 Atlantic hurricane season, and Hurricane Edouard of 1996 may have been annular hurricanes. Hurricane Epsilon of the 2005 Atlantic hurricane season had a similar structure to an annular hurricane, which partially explains the storm's longevity in the face of unfavorable conditions. Powerful Hurricane Isabel from 2003 also generated an annular hurricane structure around the time of its peak intensity.
2006's Hurricane Daniel in the eastern Pacific (image shown at the above at the right) exhibited annular hurricane features with a large, well defined eye and was described as such by the United States' National Hurricane Center. Hurricane Daniel was able to retain Category 4 intensity for a lengthy period of time, and in parts of the Eastern Pacific basin which at the time were unfavorable for such sustained intensity.
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as a supplement here's a discussion of Hurricane Episilon from NHC, mentioning the annular aspect potential:
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CZC MIATCDAT4 ALL
TTAA00 KNHC DDHHMM
HURRICANE EPSILON DISCUSSION NUMBER 26
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
4 PM EST MON DEC 05 2005
THE CLOUD PATTERN CONTINUES TO BE REMARKABLY WELL-ORGANIZED FOR A
HURRICANE AT SUCH HIGH LATITUDE IN DECEMBER. IT HAS A WELL-DEFINED
LARGE EYE SURROUNDED BY A RING OF CONVECTION...AND THE OUTFLOW IS
ESTABLISHED IN ALL QUADRANTS. EPSILON RESEMBLES ONE OF THESE
ANNULAR HURRICANES OR "TRUCK TIRE PATTERN" DESCRIBED IN THE
SCIENTIFIC LITERATURE. ALTHOUGH THIS CLASSIFICATION IS FOR
HURRICANES IN THE DEEP TROPICS...EPSILON HAS INDEED MAINTAINED ITS
INTENSITY...MORE THAN ANTICIPATED.
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Annular hurricane
Wikipedia, the free encyclopedia - Cite This Source
An annular 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 with eyewall replacement cycles, unlike typical intense tropical cyclones. Annular hurricanes also tend to persist, even when encountering environmental conditions which easily dissipate most other hurricanes. Forecasters have difficulty predicting the behavior of annular hurricanes; they are a recently recognized phenomenon, and as such, little is known about their tendencies. Because of this, they can be more dangerous than typical hurricanes.
Characteristics
Annular hurricanes are axisymmetric — symmetric along every radial axis, i.e. very circular in appearance. They lack the spiralform rainbands which are characteristic of typical tropical cyclones. After reaching peak intensity, they weaken much more slowly than non-annular storms of similar intensity. However, most annular hurricanes have annular characteristics for only a portion of their lifetimes.
While hurricanes retain annular characteristics, they also seem to be less affected by diurnal, or daily variations. Most annular hurricanes have peak intensities of greater than 85 knots (100 mph, 155 km/h) and more than 85% of their theoretical maximum potential intensity.
Annular hurricanes maintain their intensities longer than usual after their peaks. Statistics show that forecasters significantly overestimate the lessening of wind velocities in annular hurricanes. In terms of the Dvorak technique, annular hurricanes weaken very slowly after their peak (on average, less than 0.5 T after one day from their peak intensities).
Annular hurricanes are very rare. Few storms meet all of the criteria, although many strong storms resemble annular hurricanes in some criteria. Fewer than 1% of Atlantic tropical cyclones encounter all of the environmental conditions associated with annular hurricanes. In the Eastern Pacific, such conditions are more common, but still very unusual — 3% of Pacific tropical cyclones encounter them.
An algorithm for objective identification, in real time, of annular hurricanes has been developed and shows skill, but it is not yet operational.
Formation
Research into the characteristics and formation of annular hurricanes is still in its infancy. First classified and categorized in 2002, little is known about how they form, or why some are able to maintain their intensity in hostile conditions.
What meteorologists do know is that a normal hurricane, after undergoing an eyewall replacement cycle, fails to re-establish the standard hurricane appearance. The new eyewall thickens, and rainbands dissipate, and the hurricane takes on an annular structure. As compared to the formation of normal hurricanes, this happens under weaker wind shear and, surprisingly, cooler sea surface temperatures.
Some of the conditions associated with annular hurricanes are:
* An intensity 85% or greater from their theoretical maximum potential intensity,
* Weak wind shear from the east or southeast,
* A cold east wind at a high altitude (the 200 mbar pressure level),
* Near-constant sea surface temperatures between 25.4 °C and 28.5 °C, and
* Lack of relative eddy flux convergence at the 200 mbar pressure level, relative to the storm.
Notable annular hurricanes
Hurricane Luis of the 1995 Atlantic hurricane season, and Hurricane Edouard of 1996 may have been annular hurricanes. Hurricane Epsilon of the 2005 Atlantic hurricane season had a similar structure to an annular hurricane, which partially explains the storm's longevity in the face of unfavorable conditions. Powerful Hurricane Isabel from 2003 also generated an annular hurricane structure around the time of its peak intensity.
2006's Hurricane Daniel in the eastern Pacific (image shown at the above at the right) exhibited annular hurricane features with a large, well defined eye and was described as such by the United States' National Hurricane Center. Hurricane Daniel was able to retain Category 4 intensity for a lengthy period of time, and in parts of the Eastern Pacific basin which at the time were unfavorable for such sustained intensity.
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as a supplement here's a discussion of Hurricane Episilon from NHC, mentioning the annular aspect potential:
--
CZC MIATCDAT4 ALL
TTAA00 KNHC DDHHMM
HURRICANE EPSILON DISCUSSION NUMBER 26
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
4 PM EST MON DEC 05 2005
THE CLOUD PATTERN CONTINUES TO BE REMARKABLY WELL-ORGANIZED FOR A
HURRICANE AT SUCH HIGH LATITUDE IN DECEMBER. IT HAS A WELL-DEFINED
LARGE EYE SURROUNDED BY A RING OF CONVECTION...AND THE OUTFLOW IS
ESTABLISHED IN ALL QUADRANTS. EPSILON RESEMBLES ONE OF THESE
ANNULAR HURRICANES OR "TRUCK TIRE PATTERN" DESCRIBED IN THE
SCIENTIFIC LITERATURE. ALTHOUGH THIS CLASSIFICATION IS FOR
HURRICANES IN THE DEEP TROPICS...EPSILON HAS INDEED MAINTAINED ITS
INTENSITY...MORE THAN ANTICIPATED.
) who make their own forecasts independent of NHC. That is likely the outlook of that meteorologist.
