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Description |
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Classification |
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Tropical vs. Subtropical ? |
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Climatology |
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Imagery Examples |
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Intensity Analysis Procedures |
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Description |
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Known by several different terms |
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Kona (Hawaii) |
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Hybrid System (Gray 1968) |
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Semitropical (Spiegler 1972) |
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Subtropical cyclones (Simpson 1952) |
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Description (continued) |
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Definition: |
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Low level manifestation of a cut-off low |
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(from
Glossary of Meteorology) |
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Can exhibit both extratropical and tropical
characteristics. |
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CAN transform into full tropical cyclones - even
hurricane intensity! |
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We are required to do fixes on these systems! |
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Classification |
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Three Different variants: |
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Cold Low |
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Frontal Wave |
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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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Classification |
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Tropical vs. Subtropical ? |
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How do you distinguish between tropical &
subtropical cyclones based on METSAT imagery? |
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Other clues? |
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Classification (continued) |
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Frontal Bands have a typical frontal cloud
structure. Look to baroclininc waves that become cut off from the regular
flow. |
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Cold Lows have a circular cloud pattern with
limited convection near center |
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Non-frontal Circulations (found east of troughs)
have an amorphous cloud structure |
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Classification (continued - Other clues) |
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Classification (continued) |
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Look for clues in the upper level pattern |
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There should be a cut off low at 500 mb! |
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See examples of flow pattern |
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Climatology |
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Past Tracks |
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Points of origin/cyclogenesis |
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Type of system |
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NOTE: Atlantic and North Pacific only. |
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IMAGE EXAMPLES |
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Azores |
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Western/Central Pacific |
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Intensity Analysis Procedures |
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Hebert / Poteat (H/P) Technique |
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Developed by National Hurricane Center |
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Study done in 1968 - 1974 |
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Better verification than Dvorak for these
systems |
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Completed July 1975 - old technique |
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Reference: |
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NOAA
Technical Memorandum NWS SR-83 |
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Hebert / Poteat (H/P) Technique |
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“ST” numbers (instead of “T” numbers) are used
to describe intensity |
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Data T Equivalent first |
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Then the Pattern T |
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No constraints |
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Hebert / Poteat (H/P) Technique (..continued..) |
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ST 1.5 (25-30 knots max sustained winds) |
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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) |
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For Cold Lows, convection MAY NOT be connected
to other systems and a small area (< 3 degrees latitude or 180 nm) of deep layer convection exists near the
center. |
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If the system meets the requirements of either
of the above statements, then the intensity is ST 1.5 |
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Hebert / Poteat (H/P) Technique (..continued..) |
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ST 2.5 (35-40 knots max sustained winds) |
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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). |
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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. |
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If the system meets the requirements of either
of the above statements, then the intensity is ST 2.5 |
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Hebert / Poteat (H/P) Technique (..continued..) |
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ST 3.0 (45-50 knots max sustained winds) |
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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. |
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There is evidence of banding near the LLCC (less
than 1 degree latitude - 60 nm - from LLCC). |
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If the system meets the requirements of either
of the above statements, then the intensity is ST 3.0 |
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Hebert / Poteat (H/P) Technique (..continued..) |
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ST 3.5 (55-60 knots max sustained winds) |
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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!). |
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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. |
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For systems moving rapidly eastward, there may
be only a dense overcast ( > 3
degrees latitude) about 2 to 4 degrees east of the LLCC |
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If the system meets the requirements of any of
the above statements, then the intensity is ST 3.5 |
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Hebert / Poteat (H/P) Technique (..continued..) |
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NOTE for ST 3.0 and 3.5 ONLY: |
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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 |
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Example: ST3.0 storm is moving 26 knots - ST3.0
becomes ST3.5 |
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Hebert / Poteat (H/P) Technique (..continued..) |
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NOTE ST 3.5 ONLY: |
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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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Hebert / Poteat (H/P) Technique (..continued..) |
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Constraints: |
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There are no documented constraints on the H/P
technique |
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No restrictions on initial classification |
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Can start the storm at ST2.5 without ‘breaking
constraints’ |
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Notes