WDPS31 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 26P (GINA) 
WARNING NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.2S 168.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 90 NM SOUTH OF PORT VILA, VANUATU
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS FLARING
SHEARED CONVECTION ASSOCIATED WITH A MOSTLY EXPOSED LOW LEVEL 
CIRCULATION CENTER (LLCC). 26P (GINA) IS QUASI-STATIONARY IN AN
AREA OF WARM SEA SURFACE TEMPERATURES, OFFSET BY AN UNFAVORABLE
ENVIRONMENT WITH HIGH NORTHWESTERLY WIND SHEAR VALUES OF 25-30
KNOTS ASSOCIATED WITH A WEAK UPPER LEVEL TROUGH TO THE NORTHWEST.
THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
EXPOSED LLCC IN ANIMATED SHORTWAVE INFRARED IMAGERY. THE INITIAL
INTENSITY OF 35 KNOTS IS BASED ON PERSISTENCE FOLLOWING A 201057Z
ASCAT-B PASS THAT SHOWED 35-40 KNOT WINDS ON THE SOUTHEAST SIDE OF
THE CIRCULATION.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   PHFO: T2.0 - 30 KTS
   CIMSS SATCON: 41 KTS AT 201418Z
   CIMSS ADT: 34 KTS AT 201740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30+ KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: DUE TO A RECENT EASTERLY JOG, THE
INITIAL POSITION AND FORECAST TRACK HAVE BEEN SHIFTED ABOUT 60 NM
EASTWARD 

FORECAST DISCUSSION: 26P (GINA) CONTINUES TO BE DISRUPTED BY STRONG
NORTHWESTERLY VERTICAL WIND SHEAR OF 25-30 KNOTS WHICH IS HELPING
TO DECOUPLE THE SYSTEM BY DISPLACING CONVECTION TO THE SOUTHEAST
QUADRANT. SHEAR IS EXPECTED TO CONTINUE INCREASING THROUGHOUT THE
FORECAST PERIOD. COMBINED WITH DEEP-LAYER DRY AIR BEING ADVECTED
OVER THE CIRCULATION, THE HIGH SHEAR WILL CAUSE GINA TO FULLY
DECOUPLE, RESULTING IN A DECREASE IN INTENSITY TO BELOW WARNING
CRITERIA BY TAU 24 AS THE STORM MOVES SOUTH OR SOUTH-SOUTHEASTWARD.
THE FORECAST THUS TERMINATES AT THAT TIME, SHOWING DISSIPATION. 

MODEL DISCUSSION: MODEL SPREAD IS SURPRISINGLY HIGH WITHIN THE NEAR
TERM WITH A SPREAD OF 45 NM AT 12 HOURS. THE GFS DETERMINISTIC
MODEL SEEMS TO BE INITIALIZING FURTHER TO THE WEST FROM WHERE THE
CURRENT BEST TRACK POSITION IS LOCATED. ECMWF SEEMS TO BE HANDLING
THE NEAR TERM EASTWARD JOG BETTER, AND THE JTWC FORECAST IS THUS
PLACED CLOSER TO THE ECMWF THAN THE GFS, AND CLOSE TO THE
MULTI-MODEL CONSENSUS. THE JTWC INTENSITY FORECAST IS CLOSE TO THE
MULTI-MODEL CONSENSUS.

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