WDPS31 PGTW 191500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 26P (GINA) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.3S 168.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 37 NM NORTHEAST OF PORT VILA, VANUATU
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS FLARING
CONVECTION WITH ASSOCIATED CIRRUS SHIELD OBSCURING THE LOW-LEVEL
CIRCULATION CENTER (LLCC). CONVECTION CONTINUES TO BE SHEARED
TOWARD THE SOUTH AS THE SYSTEM INTERACTS WITH A HIGH-AMPLITUDE
TROUGH TO THE WEST. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE, WITH THE POSITION OF THE LLCC ASSESSED TO BE NEAR THE
PERSISTENT REGION OF OVERSHOOTING TOPS TOWARD THE NORTHERN
PERIPHERY OF THE DEEPEST CONVECTION. SURFACE WIND OBSERVATION FROM
PORT VILA, VANUATU IS SUSTAINED AT 16 KNOTS GUSTING TO 32 KNOTS,
SUGGESTING THAT TROPICAL STORM FORCE WINDS ARE LIKELY ISOLATED
WITHIN THE BRIEF BURSTS OF DEEP CONVECTION. GIVEN THE LACK OF
SCATTEROMETRY DATA, THE INITIAL INTENSITY IS HELD AT 35 KNOTS
PRIMARILY BASED ON A BLEND OF AGENCY DVORAK ESTIMATES.

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
   NFFN: T3.0 - 45 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 28-29 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 CONTINUES TO EXHIBIT FLARING CONVECTION
NEAR THE LLCC, BUT THE CONVECTIVE STRUCTURE REMAINS STEADY STATE.
GIVEN THE MODERATE VERTICAL WIND SHEAR AND LAND INTERACTION WITH
THE ISLANDS OF VANUATU, THE SYSTEM IS FORECAST TO MAINTAIN ITS
CURRENT INTENSITY FOLLOWED BY SOME SLIGHT WEAKENING. AT THIS TIME,
THE LLCC REMAINS ALONG THE NORTHERN PERIPHERY OF THE FLARING
CONVECTION. IN THE NEAR TERM THROUGH TAU 24, ENVIRONMENTAL
CONDITIONS SHOULD CONTINUE TO REMAIN MARGINAL, WITH INTENSITY
LIKELY TO HOLD AT AROUND 35 KNOTS. AFTER TAU 24,
VERTICAL WIND SHEAR IS FORECAST TO INCREASE, AND WITH COOLING SEA
SURFACE TEMPERATURES AND AN INCREASE IN DRY AIR ENTRAINMENT, TC 26P
IS FORECAST TO DISSIPATE BY TAU 36 TO 48. THE REMNANT OF TC 26P IS
THEN FORECAST TO TURN TOWARD THE SOUTHEAST BEYOND TAU 48, WHICH IS
INDICATED BY THE EXTRA FORECAST POSITION.

MODEL DISCUSSION: ALTHOUGH TC 26P HAS JOGGED SOUTHWARD OVER THE
LAST 6 HOURS, NUMERICAL MODEL GUIDANCE CONTINUES TO AGREE ON A
SOUTHWESTWARD TRACK, WITH AN EVENTUAL TURN TOWARD THE SOUTH AND
SOUTHEAST. THE GFS CONTINUES TO INITIALIZE A DEEPER VORTEX,
RESULTING IN A MORE WESTWARD MOVEMENT COMPARED TO THE ECMWF AND
NAVGEM, WHICH FALL ALONG THE CENTER AND EASTERN PORTIONS OF THE
GUIDANCE ENVELOPE. THE OFFICIAL JTWC TRACK FOLLOWS CLOSE TO
CONSENSUS AND THE ECMWF SOLUTIONS. THE INTENSITY FORECAST IS HELD
AT 35 KNOTS DESPITE THE MORE AGGRESSIVE COAMPS-TC SUGGESTING
INTENSIFICATION TO 50 KNOTS, GIVEN THAT THE INTENSIFICATION PREDICTED 
BY THE INTENSITY GUIDANCE HAS NOT MATERIALIZED OVER THE LAST 12 TO 18 
HOURS AND GIVEN THE SHEARED STRUCTURE AND STEADY-STATE NATURE OF THE 
SYSTEM IN THE PRESENT MARGINAL ENVIRONMENT.

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