cloud patterns in subtropical cyclones / hybrid systems

Cloud Patterns in Subtropical Cyclones / Hybrid Systems

Cloud Patterns in SubtropicalCyclones / Hybrid Systems

AFWA/XOGM

Cloud Patterns in Subtropical Cloud Patterns in Subtropical Cyclones / Hybrid SystemsCyclones / Hybrid Systems

• DescriptionDescription

• ClassificationClassification– Tropical vs. Subtropical ?Tropical vs. Subtropical ?

• ClimatologyClimatology

• Imagery ExamplesImagery Examples

• Intensity Analysis ProceduresIntensity Analysis Procedures

• DescriptionDescription– Known by several different termsKnown by several different terms

• Kona (Hawaii)Kona (Hawaii)• Hybrid System (Gray 1968)Hybrid System (Gray 1968)• Semitropical (Spiegler 1972)Semitropical (Spiegler 1972)• Subtropical cyclones (Simpson 1952)Subtropical cyclones (Simpson 1952)


• Description (continued)Description (continued)– Definition:Definition:

• Low level manifestation of a cut-off lowLow level manifestation of a cut-off low

(from Glossary of Meteorology)(from Glossary of Meteorology)

• Can exhibit both extratropical and tropical Can exhibit both extratropical and tropical characteristics.characteristics.

• CAN transform into full tropical cyclones - CAN transform into full tropical cyclones - even hurricane intensity!even hurricane intensity!

• We are required to do fixes on these systems!We are required to do fixes on these systems!



Definition (Glossary of Meteorology, 2nd Edition)Definition (Glossary of Meteorology, 2nd Edition)

• ClassificationClassification– Three Different variants:Three Different variants:

• Cold LowCold Low

• Frontal WaveFrontal Wave

• Circulation that develops east of low Circulation that develops east of low latitude troughs, but is not a frontal latitude troughs, but is not a frontal wave or low (has no true fronts - no air wave or low (has no true fronts - no air mass discontinuity) mass discontinuity)


• ClassificationClassification– Tropical vs. Subtropical ?Tropical vs. Subtropical ?

• How do you distinguish between How do you distinguish between tropical & subtropical cyclones based tropical & subtropical cyclones based on METSAT imagery?on METSAT imagery?

• Other clues?Other clues?



• Classification (continued)Classification (continued)– Frontal BandsFrontal Bands have a typical frontal cloud structure. have a typical frontal cloud structure.

Look to baroclininc waves that become cut off from the Look to baroclininc waves that become cut off from the regular flow.regular flow.

– Cold LowsCold Lows have a circular cloud pattern with limited have a circular cloud pattern with limited convection near centerconvection near center

– Non-frontal CirculationsNon-frontal Circulations ( (found east of found east of troughs)troughs) have an amorphous cloud structurehave an amorphous cloud structure

• Classification (continued - Other clues)Classification (continued - Other clues)SSuubbttrrooppiiccaall TTrrooppiiccaall

MMaaiinnCCoonnvveeccttiioonn

PPoolleewwaarrdd aanndd eeaassttwwaarrdd ffrroommCCeenntteerr ((NN..HH..))

EEqquuaattoorrwwaarrdd aanndd eeaassttwwaarrddffrroomm cceenntteerr ((NN..HH))

CClloouudd ssyysstteemmssiizzee

WWiiddtthh 1155 ddeeggrreeeess llaattiittuuddee oorrmmoorree

WWiiddtthh uussuuaallllyy lleessss tthhaann 1100ddeeggrreeeess llaattiittuuddee

IInntteerraaccttiioonn ww//eennvviirroonnmmeenntt

CCoonnvveeccttiivvee cclloouudd ssyysstteemmrreemmaaiinnss ccoonnnneecctteedd ttoo ootthheerrssyynnooppttiicc ssyysstteemm((ss)),, ssuucchh aass550000 mmbb ttoouugghh// vvoorrttiicciittyy mmaaxx..

CClloouudd ssyysstteemmbbeeccoommeess iissoollaatteedd –– nnooiinnfflluueennccee ffrroomm ttrroouugghhss,,sshhoorrtt wwaavveess



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

Cut -off lowCut -off low

500 mb heights500 mb heightsNOGAPS AnalysisNOGAPS Analysis

Cut -off lowCut -off low

• ClimatologyClimatology– Past TracksPast Tracks– Points of origin/cyclogenesisPoints of origin/cyclogenesis– Type of systemType of system– NOTE: Atlantic and North NOTE: Atlantic and North

Pacific only. Pacific only.


Climatology: Subtropical Cyclones Climatology: Subtropical Cyclones

A: Cold LowB-1: Frontal WaveB-2: LLCC east of U/L trough


Hawaii


IMAGE EXAMPLESIMAGE EXAMPLES

• AzoresAzores

• Western/Central Pacific Western/Central Pacific


Subtropical CyclonesSubtropical CyclonesAzoresAzores

Subtropical CyclonesSubtropical CyclonesCentral PacificCentral Pacific

Subtropical CyclonesCentral Pacific

• Intensity Analysis ProceduresIntensity Analysis Procedures– Hebert / Poteat (H/P) Technique Hebert / Poteat (H/P) Technique

• Developed by National Hurricane CenterDeveloped by National Hurricane Center

• Study done in 1968 - 1974Study done in 1968 - 1974

• Better verification than Dvorak for these Better verification than Dvorak for these systemssystems

• Completed July 1975 - old techniqueCompleted July 1975 - old technique

• Reference: Reference:

NOAA Technical Memorandum NWS SR-83NOAA Technical Memorandum NWS SR-83


• Hebert / Poteat (H/P) Technique Hebert / Poteat (H/P) Technique – ““ST” numbers (instead of “T” numbers) are ST” numbers (instead of “T” numbers) are

used to describe intensityused to describe intensity– Data T Equivalent firstData T Equivalent first– Then the Pattern TThen the Pattern T– No constraintsNo constraints


• Hebert / Poteat (H/P) Technique (..continued..)Hebert / Poteat (H/P) Technique (..continued..)• ST 1.5 (25-30 knots max sustained winds)ST 1.5 (25-30 knots max sustained winds)

– Low Level Circulation Center is displaced from Low Level Circulation Center is displaced from poorly organized poorly organized convectionconvection (not necessarily dense convection) by at least 0.5 (not necessarily dense convection) by at least 0.5 degrees latitude (30 nm) but no more than 2 degrees (120 nm)degrees latitude (30 nm) but no more than 2 degrees (120 nm)

– For Cold Lows, convection MAY NOT be connected to other For Cold Lows, convection MAY NOT be connected to other systems and a small area (< 3 degrees latitude or 180 nm) of systems and a small area (< 3 degrees latitude or 180 nm) of deep layer convection exists near the center.deep layer convection exists near the center.

– If the system meets the requirements of either of the above If the system meets the requirements of either of the above statements, then the intensity is statements, then the intensity is ST 1.5ST 1.5


• Hebert / Poteat (H/P) Technique (..continued..)Hebert / Poteat (H/P) Technique (..continued..)• ST 2.5 (35-40 knots max sustained winds)ST 2.5 (35-40 knots max sustained winds)

– Low Level Circulation Center is displaced from Low Level Circulation Center is displaced from increased deep layer, organized increased deep layer, organized convectionconvection (not necessarily dense convection) by at least 0.5 degrees latitude (30 (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 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 more markedly curved spiral band pattern (as a rough guide, it should wrap at least 0.5 divisions on the Log10 spiral).least 0.5 divisions on the Log10 spiral).

– The outer convective band should be displaced 5 to 10 degrees latitude (300-600 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) nm) east of the the LLCC and possibly another exists 2 to 4 degrees (120-240 nm) west through north of the LLCC. west through north of the LLCC.

– If the system meets the requirements of either of the above statements, then the If the system meets the requirements of either of the above statements, then the intensity is intensity is ST 2.5ST 2.5


• Hebert / Poteat (H/P) Technique Hebert / Poteat (H/P) Technique (..continued..)(..continued..)• ST 3.0 (45-50 knots max sustained winds)ST 3.0 (45-50 knots max sustained winds)

– Same criteria as with ST 2.5, except the system should exhibit Same criteria as with ST 2.5, except the system should exhibit greater SBC and better organized convection than the greater SBC and better organized convection than the previous day. Overcast may be dense.previous day. Overcast may be dense.

– There is evidence of banding near the LLCC (less than 1 There is evidence of banding near the LLCC (less than 1 degree latitude - 60 nm - from LLCC).degree latitude - 60 nm - from LLCC).

– If the system meets the requirements of either of the above If the system meets the requirements of either of the above statements, then the intensity is statements, then the intensity is ST 3.0ST 3.0


• Hebert / Poteat (H/P) Technique Hebert / Poteat (H/P) Technique (..continued..)(..continued..)• ST 3.5 (55-60 knots max sustained winds)ST 3.5 (55-60 knots max sustained winds)

– Deep layer convection (frequently with dense overcast) is evident in band(s) 1 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 to 3 degrees latitude (60 - 180 nm) from LLCC (NO CENTRAL DENSE OVERCAST!).OVERCAST!).

– The outer, eastern convective band (5 to 10 degrees latitude from the LLCC) 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.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 For systems moving rapidly eastward, there may be only a dense overcast ( ( >> 3 degrees latitude) about 2 to 4 degrees east of the LLCC 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 If the system meets the requirements of any of the above statements, then the intensity is intensity is ST 3.5ST 3.5


• Hebert / Poteat (H/P) Technique Hebert / Poteat (H/P) Technique (..continued..)(..continued..)• NOTE for ST 3.0 and 3.5 ONLY:NOTE for ST 3.0 and 3.5 ONLY:

– If the forward speed of the system exceeds 20 knots, the If the forward speed of the system exceeds 20 knots, the excess speed should be added to the maximum wind speed excess speed should be added to the maximum wind speed obtained by the criteria for ST 3.0/3.5obtained by the criteria for ST 3.0/3.5

– Example: ST3.0 storm is moving 26 knots - ST3.0 becomes Example: ST3.0 storm is moving 26 knots - ST3.0 becomes ST3.5ST3.5


• Hebert / Poteat (H/P) Technique Hebert / Poteat (H/P) Technique (..continued..)(..continued..)• NOTE ST 3.5 ONLY:NOTE ST 3.5 ONLY:

– SSM/I GALE WIND RADII BULLETINS MUST BE SSM/I GALE WIND RADII BULLETINS MUST BE COMPLETED FOR SYSTEMS THAT ATTAIN AN COMPLETED FOR SYSTEMS THAT ATTAIN AN INTENSITY OF ST3.5INTENSITY OF ST3.5


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

• Hebert / Poteat (H/P) Technique Hebert / Poteat (H/P) Technique (..continued..)(..continued..)

• Constraints:Constraints:

– There are no documented constraints on the H/P There are no documented constraints on the H/P techniquetechnique

– No restrictions on initial classificationNo restrictions on initial classification

– Can start the storm at ST2.5 without Can start the storm at ST2.5 without ‘breaking ‘breaking constraints’constraints’


Questions?

Developed by Paul McCrone, Chief ForecasterDeveloped by Paul McCrone, Chief ForecasterAir Force Weather Agency, Global Weather DivisionAir Force Weather Agency, Global Weather DivisionMETSAT Applications Branch (Office: XOGM)METSAT Applications Branch (Office: XOGM)[email protected] - DSN [email protected] - DSN 271-2821

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cloud patterns in subtropical cyclones / hybrid systems

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