Cloud Patterns in Subtropical Cyclones / Hybrid Systems

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems
Cloud Patterns in Subtropical Cyclones / Hybrid
Systems
AFWA/XOGM
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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Description
• Classification
• Tropical vs. Subtropical ?
• Climatology
• Imagery Examples
• Intensity Analysis Procedures

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Description
• Known by several different terms
• Kona (Hawaii)
• Hybrid System (Gray 1968)
• Semitropical (Spiegler 1972)
• Subtropical cyclones (Simpson 1952)

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Description (continued)
• Definition
• Low level manifestation of a cut-off low
• (from Glossary of Meteorology)
• Can exhibit both extratropical and tropical
  characteristics.
• CAN transform into full tropical cyclones - even
  hurricane intensity!
• We are required to do fixes on these systems!

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems
Definition (Glossary of Meteorology, 2nd Edition)
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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Classification
• Three Different variants
• Cold Low
• Frontal Wave
• Circulation that develops east of low latitude
  troughs, but is not a frontal wave or low (has no
  true fronts - no air mass discontinuity)

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Classification
• Tropical vs. Subtropical ?
• How do you distinguish between tropical
  subtropical cyclones based on METSAT imagery?
• Other clues?

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Classification (continued)
• Frontal Bands have a typical frontal cloud
  structure. Look to baroclininc waves that become
  cut off from the regular flow.
• Cold Lows have a circular cloud pattern with
  limited convection near center
• Non-frontal Circulations (found east of troughs)
  have an amorphous cloud structure

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Classification (continued - Other clues)

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Classification (continued)
• Look for clues in the upper level pattern
• There should be a cut off low at 500 mb!
• See examples of flow pattern

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Cut -off low
500 mb heights NOGAPS Analysis
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Cut -off low
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Cut -off low
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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Climatology
• Past Tracks
• Points of origin/cyclogenesis
• Type of system
• NOTE Atlantic and North Pacific only.

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Climatology Subtropical Cyclones
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Climatology Subtropical Cyclones
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Climatology Subtropical Cyclones
A Cold Low B-1 Frontal Wave B-2 LLCC
east of U/L trough
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Climatology Subtropical Cyclones
Hawaii
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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• IMAGE EXAMPLES
• Azores
• Western/Central Pacific

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Subtropical Cyclones Azores
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Subtropical Cyclones Azores
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Subtropical Cyclones Azores
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Subtropical Cyclones Azores
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Subtropical Cyclones Azores
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Subtropical Cyclones Central Pacific
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Subtropical Cyclones Central Pacific
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Subtropical Cyclones Central Pacific
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Subtropical Cyclones Central Pacific
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Subtropical Cyclones Central Pacific
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Subtropical Cyclones Central Pacific
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Subtropical Cyclones Central Pacific
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Subtropical Cyclones Central Pacific
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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Intensity Analysis Procedures
• Hebert / Poteat (H/P) Technique
• Developed by National Hurricane Center
• Study done in 1968 - 1974
• Better verification than Dvorak for these systems
• Completed July 1975 - old technique
• Reference
• NOAA Technical Memorandum NWS SR-83

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Hebert / Poteat (H/P) Technique
• ST numbers (instead of T numbers) are used to
  describe intensity
• Data T Equivalent first
• Then the Pattern T
• No constraints

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Hebert / Poteat (H/P) Technique (..continued..)
• ST 1.5 (25-30 knots max sustained winds)
• Low Level Circulation Center is displaced from
  poorly organized convection (not necessarily
  dense convection) by at least 0.5 degrees
  latitude (30 nm) but no more than 2 degrees (120
  nm)
• For Cold Lows, convection MAY NOT be connected to
  other systems and a small area (lt 3 degrees
  latitude or 180 nm) of deep layer convection
  exists near the center.
• If the system meets the requirements of either of
  the above statements, then the intensity is ST
  1.5

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Hebert / Poteat (H/P) Technique (..continued..)
• ST 2.5 (35-40 knots max sustained winds)
• Low Level Circulation Center is displaced from
  increased deep layer, organized convection (not
  necessarily dense convection) by at least 0.5
  degrees latitude (30 nm) but no more than 2
  degrees (120 nm). The cloud pattern should
  exhibit a more markedly curved spiral band
  pattern (as a rough guide, it should wrap at
  least 0.5 divisions on the Log10 spiral).
• The outer convective band should be displaced 5
  to 10 degrees latitude (300-600 nm) east of the
  the LLCC and possibly another exists 2 to 4
  degrees (120-240 nm) west through north of the
  LLCC.
• If the system meets the requirements of either of
  the above statements, then the intensity is ST
  2.5

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Hebert / Poteat (H/P) Technique (..continued..)
• ST 3.0 (45-50 knots max sustained winds)
• Same criteria as with ST 2.5, except the system
  should exhibit greater SBC and better organized
  convection than the previous day. Overcast may be
  dense.
• There is evidence of banding near the LLCC (less
  than 1 degree latitude - 60 nm - from LLCC).
• If the system meets the requirements of either of
  the above statements, then the intensity is ST
  3.0

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Hebert / Poteat (H/P) Technique (..continued..)
• ST 3.5 (55-60 knots max sustained winds)
• Deep layer convection (frequently with dense
  overcast) is evident in band(s) 1 to 3 degrees
  latitude (60 - 180 nm) from LLCC (NO CENTRAL
  DENSE OVERCAST!).
• The outer, eastern convective band (5 to 10
  degrees latitude from the LLCC) is weaker than
  the day before, but a new band may be forming to
  the west.
• For systems moving rapidly eastward, there may be
  only a dense overcast ( gt 3 degrees latitude)
  about 2 to 4 degrees east of the LLCC
• If the system meets the requirements of any of
  the above statements, then the intensity is ST 3.5

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Hebert / Poteat (H/P) Technique (..continued..)
• NOTE for ST 3.0 and 3.5 ONLY
• If the forward speed of the system exceeds 20
  knots, the excess speed should be added to the
  maximum wind speed obtained by the criteria for
  ST 3.0/3.5
• Example ST3.0 storm is moving 26 knots - ST3.0
  becomes ST3.5

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Hebert / Poteat (H/P) Technique (..continued..)
• NOTE ST 3.5 ONLY
• SSM/I GALE WIND RADII BULLETINS MUST BE COMPLETED
  FOR SYSTEMS THAT ATTAIN AN INTENSITY OF ST3.5

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• Hebert / Poteat (H/P) Technique Pattern T

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Cloud Patterns in Subtropical Cyclones / Hybrid
Systems

• Hebert / Poteat (H/P) Technique (..continued..)
• Constraints
• There are no documented constraints on the H/P
  technique
• No restrictions on initial classification
• Can start the storm at ST2.5 without breaking
  constraints

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Questions?
Questions?
Developed by Paul McCrone, Chief Forecaster Air
Force Weather Agency, Global Weather
Division METSAT Applications Branch (Office
XOGM) Paul.McCrone_at_afwa.af.mil - DSN 271-2821