Advisories

WDPN31 PGTW 140900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT) 
WARNING NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.3N 142.8E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 226 NM SOUTH-SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY 
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC). OVER THE PAST FOUR 
HOURS, MODERATE CONVECTION HAS DEVELOPED PROXIMATE TO THE INNER CORE 
OF THE SYSTEM; HOWEVER, PERSISTENCE AND CORE CONSOLIDATION REMAIN 
HIGHLY UNCERTAIN. ANIMATED WATER VAPOR IMAGERY AND ATMOSPHERIC MOTION 
VECTOR (AMV) ANALYSIS DEPICT A WEAK UPPER-LEVEL LOW (ULL) POSITIONED 
JUST SOUTHWEST OF TD 28W, FACILITATING A TRANSIENT BURST OF WEAK 
POLEWARD OUTFLOW THAT IS LIKELY FUELING THE NASCENT CONVECTION. THE 
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE 
EXPOSED LLCC RESOLVED IN MSI. THE INITIAL INTENSITY IS ASSESSED WITH 
HIGH CONFIDENCE, CROSS-VALIDATED WITH RECENT SCATTEROMETER DATA AND 
ALIGNED WITH SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES NOTED 
BELOW. ENVIRONMENTAL CONDITIONS REMAIN MARGINAL, WITH LOW VWS AND 
WARM SSTS OFFSET BY SIGNIFICANT RESTRICTIONS IN UPPER-LEVEL DIVERGENT 
OUTFLOW AND HOSTILE DRY AIR ENTRAINMENT.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED FAR TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   CIMSS SATCON: 36 KTS AT 140346Z
   CIMSS ADT: 25 KTS AT 140540Z
   CIMSS AIDT: 31 KTS AT 140540Z
   CIMSS D-MINT: 26 KTS AT 140347Z
   CIMSS D-PRINT: 25 KTS AT 140610Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: DRY MID-LEVEL AIR, HIGHLY RESTRICTED OUTFLOW
ALOFT.

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST HAS BEEN EXTENDED TO 36
HOURS. 

FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 28W IS FORECAST TO
TRACK NORTHWESTWARD ALONG THE SOUTHWESTERN FLANK OF THE STR THROUGH
THE ENTIRE FORECAST PERIOD. AS RESOLVED IN RECENT MODEL GUIDANCE, THE 
ATMOSPHERE EXHIBITS SLIGHT NEAR-TERM MOISTURE RECOVERY. THIS 
EVOLUTION, COMBINED WITH A MODEST SOUTHWESTWARD DISPLACEMENT OF THE
ULL, HAS IMPROVED OUTFLOW DIVERGENCE ALOFT, GENERATING CONVECTIVE 
FLARES IN AND AROUND THE INNER CORE THIS EVENING. HOWEVER, SUSTAINED 
ORGANIZED CONVECTIVE CONSOLIDATION REMAINS IMPROBABLE. NUMERICAL 
MODELS INDICATE THE CYCLONE WILL TRANSIT INTO AN EXTREMELY DRY 
ATMOSPHERE TO THE NORTHWEST WITHIN THE NEXT 12 HOURS, PRECLUDING 
CONVECTIVE PERSISTENCE BEYOND A BRIEF TEMPORARY TIMELINE. 
ADDITIONALLY, GLOBAL DYNAMICAL MODELS PROJECT A STEADY INCREASE IN 
DEEP-LAYER VERTICAL WIND SHEAR (VWS) COMMENCING WITHIN THE NEXT 12 TO 
24 HOURS, PROGRESSIVELY AMPLIFYING THROUGH THE REMAINDER OF THE 
FORECAST. THE COMBINED THERMODYNAMIC AND KINEMATIC CORROSION WILL 
GRADUALLY DEGRADE AND DISSIPATE THE LOWER-LEVEL VORTEX. GIVEN THE 
RESILIENCE OF THE SHALLOW CIRCULATION, CONSENSUS GUIDANCE PROJECTS 
RETENTION OF A 25-KNOT SURFACE CORE SLIGHTLY LONGER THAN PREVIOUSLY 
ASSESSED; ACCORDINGLY, SYSTEM DISSIPATION BELOW WARNING CRITERIA IS 
NOW PROJECTED BY TAU 36. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN STRONG AGREEMENT, WITH
LITTLE IN THE WAY OF EITHER ALONG- OR CROSS-TRACK UNCERTAINTY. THE
JTWC FORECAST IS POSITIONED NEAR THE MULTI-MODEL CONSENSUS MEAN
WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT, WITH
ALL MEMBERS OF THE CONSENSUS INDICATING A PERIOD OF STAGNATION AT
25 KNOTS FOLLOWED BY DISSIPATION, THE ONLY UNCERTAINTY IS THE
TIMING. THE DEEPMIND, GFS AND CTCX DEPICT THE SYSTEM DISSIPATING BY
TAU 36, WHILE THE HAFS-A AND SHIPS-GFS HOLD THE SYSTEM AT 25 KNOTS
UNTIL TAU 48 BEFORE DISSIPATION BY TAU 60. THE JTWC FORECAST FAVORS
THE DEEPMIND AND CTCX SOLUTION WITH HIGH CONFIDENCE. 

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