WDPS31 PGTW 190300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 26P (GINA) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.7S 169.0E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 127 NM NORTH-NORTHEAST OF PORT VILA,
VANUATU
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW LEVEL CIRCULATION WITH DEEP CONVECTION PRIMARILY
SHEARED WELL TO THE SOUTHEAST AS A HIGH-AMPLITUDE MID-LEVEL TROUGH
APPROACHES FROM THE WEST, HOWEVER, A FRESH POCKET OF CONVECTION IS
BUILDING TOWARDS THE SOUTHWESTERN QUADRANT OF THE CORE. DESPITE A
LACK OF RECENT MICROWAVE IMAGERY, THE INITIAL POSITION WAS PLACED
WITH HIGH CONFIDENCE BASED ON THE APPEARANCE IN MSI. THE INITIAL
INTENSITY WAS HELD AT 35 KNOTS BASED ON AVAILABLE DVORAK ESTIMATES
AND ADT, ALTHOUGH TROPICAL STORM FORCE WINDS ARE LIKELY ISOLATED TO
THE SOUTHEAST QUADRANT UNDER THE DEEP CONVECTION UNLESS THE NEW 
CENTRAL CONVECTION PERSISTS. BOTH DESCENDING ASCAT PASSES MISSED THE 
CIRCULATION AND NO OTHER RECENT SCATTEROMETRY OR NEARBY SURFACE 
OBSERVATIONS ARE AVAILABLE TO CONFIRM THE WINDS OR STRUCTURE.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: A MID-LEVEL REFLECTION OF A
SUB-TROPICAL RIDGE TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 34 KTS AT 182340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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, ALTHOUGH FORECAST LENGTH
HAS BEEN SHORTENED TO 72 HOURS.

FORECAST DISCUSSION: DESPITE THE WELL DEFINED SURFACE CIRCULATION,
GINA IS STRUGGLING TO OVERCOME THE EFFECTS OF THE MODERATE VWS, AND
PASSAGE OVER THE ISLANDS OF VANUATU MAY FURTHER INHIBIT CONVECTIVE
ORGANIZATION. MODEL GUIDANCE IS IN GENERALLY GOOD AGREEMENT ON THE
SOUTHWESTERLY MOTION, HOWEVER, GFS IS ANALYZING THE INITIAL
POSITION TO THE SOUTHEAST, AND CONSEQUENTLY OVER ESTIMATING THE
STRENGTH OF THE WIND FIELD WHICH CARRIES OVER INTO A MUCH DEEPER
SYSTEM THAN OTHER MODELS SUCH AS ECMWF. INTENSITIES WERE HELD TO 35
KNOTS THROUGH TAU 36, AS MODERATE VWS PERSISTS. AFTER THAT TIME VWS
INCREASES TO 30 KNOTS AND THE MID-LEVEL ENVIRONMENT BECOMES
SIGNIFICANTLY DRIER. DISSIPATION AS A TROPICAL CYCLONE IS FORECAST
BY TAU 48. ONE EXTRA POSITION WAS ADDED TO REFLECT THE EXPECTED
DEFLECTION OF THE REMNANT TRACK AS IT CURVES TO THE SOUTH AND
SOUTHEAST WITH THE LOW LEVEL FLOW. DISSIPATION BEFORE TAU 48 IS A
POSSIBILITY IF 20 KNOT VWS PERSISTS. 

MODEL DISCUSSION: DUE TO THE CONCERNS ABOUT THE GFS ANALYSIS, THE
FORECAST FAVORS THE ECMWF SOLUTION, AND IS PLACED CLOSE TO THE
PRIOR FORECAST TRACK. THE PEAK INTENSITY WAS LIKEWISE CURTAILED
GIVEN LOWER CONFIDENCE IN THE DEEPENING OBSERVED IN THE GFS AND
HWRF MODELS. 

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