WDPS31 PGTW 200300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 26P (GINA) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.3S 167.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 46 NM SOUTHWEST OF PORT VILA, VANUATU
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW-LEVEL CIRCULATION (LLC) SOUTHWEST OF PORT VILA.
CONVECTION HAS DECREASED IN COVERAGE AND INTENSITY DURING THE PAST
SIX HOURS, AND IS NOW RAGGED AND CONFINED ONLY TO THE SOUTHEAST
QUADRANT. THE LLC REMAINS COMPACT AND VIGOROUS, WITH A 192227Z
ASCAT-B PASS REVEALING MAXIMUM WINDS OF 35 KT ON THE EASTERN SIDE.
THE INITIAL INTENSITY IS SET AT 35 KT BASED ON THIS SCATTEROMETER
DATA. WHILE MODERATE POLEWARD OUTFLOW IS OBSERVED IN MSI IMAGERY
TOWARD THE SOUTHEAST, VERTICAL SHEAR HAS ALSO INCREASED TO NEAR 25
KT, EVIDENCED BY UPPER-LEVEL CIRRUS STREAMING ACROSS THE LLC FROM
THE NORTHWEST.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 42 KTS AT 192224Z
   CIMSS ADT: 43 KTS AT 192340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DEEP-LAYER DRY AIR TO THE WEST AND NORTH

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE 26P (GINA) IS PROGRESSIVELY
SUFFERING MORE FROM INCREASING VERTICAL SHEAR, WHICH IS FORECAST TO
INCREASE FROM 25 KT TO 40 KT DURING THE NEXT 48 HOURS. DRY AIR HAS
ALREADY ENVELOPED MOST OF THE LOW-LEVEL CIRCULATION (LLC), LIMITING
CONVECTION TO THE SOUTHEAST QUADRANT. PERIODIC CONVECTIVE BURSTS
CLOSE TO THE LLC ON THE SOUTHEAST SIDE MAY SUSTAIN THE CURRENT 35
KT INTENSITY FOR ABOUT 24-36 HOURS, BUT THE AFOREMENTIONED SHEAR
AND DRY AIR ARE EXPECTED TO EVENTUALLY LEAD TO DISSIPATION BY 36-48
HOURS. GINA IS TRACKING SOUTHWESTWARD AROUND THE SUBTROPICAL RIDGE
TO ITS EAST, AND IS EXPECTED TO TURN SOUTH AND THEN SOUTHEASTWARD
BY 48 HOURS AS IT ROUNDS THE PERIPHERY OF THIS RIDGE. THE PRIMARY
SOURCE OF TRACK UNCERTAINTY IS LIKELY THE VARYING DEGREES TO WHICH
NUMERICAL MODELS DEPICT CONVECTIVE BURSTS TUGGING THE LLC
SOUTHEASTWARD. THE EXACT TIME WHEN THE LLC BECOMES COMPLETELY
DECOUPLED AND SEPARATED FROM THE CONVECTION IS SOMEWHAT UNCERTAIN
AND AFFECTS BOTH THE TRACK AND INTENSITY FORECASTS. CONFIDENCE IN
BOTH THE TRACK AND INTENSITY FORECAST ARE THUS MEDIUM.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS JUST WEST OF BUT CLOSE
TO THE MULTI-MODEL CONSENSUS, CORRECTING SLIGHTLY FOR THE EASTWARD
OUTLIER NAVGEM. THE JTWC INTENSITY FORECAST IS SLIGHTLY BELOW THE
MULTI-MODEL CONSENSUS DUE TO THE EXPECTATION THAT ANY
INTENSIFICATION OF 26P IS UNLIKELY IN THE CURRENTLY UNFAVORABLE
ENVIRONMENT.

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