WDXS31 PGTW 170300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 07S (BAKUNG) WARNING 
NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.0S 93.0E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 229 NM WEST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS TROPICAL
CYCLONE 07S (BAKUNG) UNEXPECTEDLY INTENSIFYING, WITH AN EYE
EMERGING IN BOTH MICROWAVE AND CONVENTIONAL SATELLITE IMAGERY
DURING THE PAST SIX HOURS. A 170037Z GPM MICROWAVE PASS SHOWED A
SYMMETRIC AND CLOSED EYEWALL, WITH MILD EYE TILT SOUTHWESTWARD WITH
HEIGHT. A COMPLEX SHEAR PROFILE CONTINUES TO IMPACT THE VORTEX,
WITH 20-25 KT SHEAR LAYERS IN THE MID-TROPOSPHERE AS THE
ENVIRONMENTAL FLOW VARIES FROM EASTERLY AT THE SURFACE TO WESTERLY
IN THE MID-TROPOSPHERE TO NORTHEASTERLY IN THE UPPER TROPOSPHERE.
UPPER-LEVEL OUTFLOW HAS EXPANDED IN ALL QUADRANTS, INCLUDING
UPSHEAR QUADRANTS TO SOME EXTENT. THE INITIAL INTENSITY IS
DIFFICULT TO MEASURE GIVEN THE RAPIDITY OF THE STRUCTURAL CHANGE,
BUT IS SET AT 65 KT BASED ON A SPECIAL DVORAK ASSESSMENT OF T4.0 TO
T4.5 AND A D-MINT ESTIMATE OF 60 KT BASED ON THE AFOREMENTIONED GPM
MICROWAVE PASS.

INITIAL WIND RADII BASIS: PERSISTENCE AND MICROWAVE STRUCTURE
ANALYSIS

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   CIMSS SATCON: 51 KTS AT 161909Z
   CIMSS ADT: 43 KTS AT 162030Z
   CIMSS AIDT: 37 KTS AT 162030Z
   CIMSS D-MINT: 47 KTS AT 161922Z
   CIMSS D-PRINT: 47 KTS AT 162300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: DRY AIR MASS IN THE WESTERN AND NORTHERN
SEMICIRCLES

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS SPECIAL INTERMEDIATE WARNING IS
BEING ISSUED TO SIGNIFICANTLY RAISE THE INITIAL AND FORECAST
INTENSITY RELATIVE TO THE PREVIOUS WARNING

FORECAST DISCUSSION: TROPICAL CYCLONE 07S (BAKUNG) HAS RAPIDLY
INTENSIFIED, DEFYING THE UNANIMOUS EXPECTATION BY AVAILABLE MODELS
THAT VORTEX DECOUPLING AND RAPID WEAKENING WOULD IMMINENTLY OCCUR.
INDEED, THE CURRENT CYCLE OF MODEL GUIDANCE MAINTAINS AN
EXPECTATION FOR DISSIPATION WITHIN 24 HOURS, AND HAS NOT YET
ASSIMILATED NEW DATA INDICATING BAKUNG'S TRUE INITIAL INTENSITY.
THE SHORT-TERM FORECAST IS THUS CHALLENGING, AS IT HINGES ON WHEN
THE VORTEX WILL ACTUALLY SUCCUMB TO THE MODERATE VERTICAL SHEAR AND
AMBIENT DRY AIR THAT ARE EXPECTED TO PERSIST OVER THE NEXT 48
HOURS. IN THEORY, THE COMPACT VORTEX SHOULD NOT BE ABLE TO
WITHSTAND THE ANALYZED VERTICAL SHEAR AND ASSOCIATED RADIAL
VENTILATION LONG-TERM. IT IS POSSIBLE THAT 07S WILL CONTINUE TO
DELAY DECAY LONGER THAN EXPECTED NOW THAT THE VORTEX HAS BECOME
MORE ROBUST AND VERTICALLY ALIGNED. THE NEW JTWC FORECAST ASSUMES
07S WILL MAINTAIN ITS PRESENT STRUCTURE AND INTENSITY FOR AT LEAST
THE NEXT 12 HOURS, FOLLOWED BY VORTEX DECOUPLING AND RAPID
WEAKENING AS DYNAMICAL GUIDANCE INSISTS WILL FOLLOW. THE ASSOCIATED
TRACK FORECAST IS FOR THE CURRENTLY SLOW-MOVING STORM TO BEGIN
MOVING NORTHWESTWARD AS THE VORTEX SHALLOWS AND BECOMES DOMINANTLY
INFLUENCED BY THE NEAR-SURFACE EASTERLY OR SOUTHEASTERLY FLOW. WITH
VORTEX DECOUPLING CLEARLY DELAYED RELATIVE TO MODEL EXPECTATION,
THE VORTEX IS DEEPER THAN ANTICIPATED, AND THE JTWC FORECAST
ACCORDINGLY SHOWS A SLOWER MOVE TOWARDS THE NORTHWEST. THE FORECAST
CONFIDENCE IN BOTH TRACK AND INTENSITY IS LOWER THAN AVERAGE,
PENDING RESOLUTION OF MODEL DIFFERENCES WITH REALITY. 

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS SLOWER THAN AND
SLIGHTLY EAST OF THE MULTI-MODEL CONSENSUS, WHICH HAS ELEVATED
CROSS-TRACK SPREAD DUE TO UNCERTAINTY IN HOW THE DECOUPLING VORTEX
INTERACTS WITH THE ENVIRONMENTAL STEERING FLOW. THE JTWC INTENSITY
FORECAST IS ABOVE THE MULTI-MODEL CONSENSUS DUE TO A DELAYED
DISSIPATION PHASE RELATIVE TO THE CONSENSUS EXPECTATION.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: LOW
   INTENSITY 00-72 HR: LOW//
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