WDPS31 PGTW 192100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 26P (GINA) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.2S 168.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 31 NM NORTH OF PORT VILA, VANUATU
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TC 26P (GINA), WAS PREVIOUSLY FORECAST TO TRACK EAST OF PORT VILA,
VANUATU, BUT IS NOW BELIEVED TO BE PROCEEDING WEST OF THAT
LOCATION. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY
DEPICTS A PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC)
WITH FLARING DEEP CONVECTION BEING SHEARED TO THE SOUTHEAST. A
191750Z SSMIS 91GHZ MICROWAVE SATELLITE IMAGE DEPICTS FRAGMENTED
LOW LEVEL CLOUD LINES WRAPPING AROUND A FAINT LLCC. THE INITIAL
POSITION IS THEREFOR PLACED WITH MEDIUM CONFIDENCE BASED ON THE EIR
AND SSMIS IMAGERY. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON AGENCY DVORAK INTENSITY ESTIMATES
RANGING FROM 30-35 KNOTS AND CIMSS ADT SHOWING SLIGHTLY HIGHER AT
39 KNOTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   PHFO: T2.5 - 35 KTS
   CIMSS ADT: 39 KTS AT 191640Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 26P (GINA) HAS BEEN CHALLENGING TO FORECAST
OVER THE PAST 48 HOURS. INCREASING VERTICAL WIND SHEAR (VWS) HAS
PERIODICALLY DECOUPLED THE LLCC AND UPPER LEVEL CIRCULATION CENTER
(ULCC), PARTIALLY OR FULLY EXPOSING THE LLCC; AFTER WHICH DIURNAL
CONVECTIVE CYCLES WOULD REINVIGORATE CONVECTION AND ONCE AGAIN
OBSCURE THE LOWER LEVELS. GIVEN THE PARTIAL EXPOSURE OF THE LLCC AT
THIS TIME, TC 26P IS LOCATED NORTH-NORTHWEST OF PORT VILA, VANUATU
IN A MARGINAL ENVIRONMENT CHARACTERIZED BY MODERATE VWS (20-25
KNOTS) AND DRY AIR ENTRAINMENT BALANCED BY WARM SEA SURFACE
TEMPERATURES (SST) AND MODERATE POLEWARD OUTFLOW ALOFT. AS A
RESULT, TC 26P IS FORECAST TO MAINTAIN CURRENT INTENSITY THROUGH
TAU 36 WITH A SMALL POSSIBILITY OF BRIEF INTENSIFICATION BEFORE
THEN. AS THE SYSTEM CONTINUES TO TRACK SOUTH-SOUTHWESTWARD VWS WILL
INCREASE, SSTS WILL COOL AND DRY AIR ENTRAINMENT WILL HAVE A
SIGNIFICANT NEGATIVE IMPACT ON INTENSITY. AS GINA PASSES THE STR
AXIS BETWEEN TAU 36 AND TAU 48, HIGH VWS AND A NOW FULLY DRY CORE
STRUCTURE WILL DISSIPATE THE SYSTEM OVER WATER. GINA'S REMNANTS
WILL CONTINUE SOUTH-SOUTHEASTWARD THROUGH TAU 72 INDICATED BY THE
FINAL FORECAST POSITION.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
WITH A SOUTHWESTWARD TRACK FOLLOWED BY AN EVENTUAL TURN
SOUTHEASTWARD. MODEL SPREAD IS LARGEST AT THIS INFLECTION POINT DUE
TO THE SLIGHT DISAGREEMENT IN THE LOCATION AND TIMING OF THE
SOUTHEASTWARD TURN. RELIABLE MODEL INTENSITY GUIDANCE IS NOTABLE,
IN THAT HWRF AND COAMPS-TC ARE UNREALISTICALLY AGGRESSIVE, SHOWING
A PEAK INTENSITY OF 50 KNOTS AT TAU 36. THE BULK OF THE GUIDANCE
HOWEVER SHOWS MINIMAL INTENSIFICATION THROUGH TAU 36 WHICH MATCHES
THE JTWC FORECAST. AS A RESULT, THE JTWC FORECAST TRACK AND
INTENSITY ARE PLACED WITH MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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