WDPS31 PGTW 190300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09P (IRENE)     
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.6S 169.3E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 127 NM SOUTH-SOUTHEAST OF PORT VILA,
VANUATU
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 24 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN EXPOSED,
BROAD LOW-LEVEL CIRCULATION (LLC) WITH DEEP CONVECTION SHEARED TO
THE SOUTHEAST. AN 182136Z MHS 89GHZ MICROWAVE IMAGE INDICATES A
CLUSTER OF INTENSE CONVECTION SHEARED TO THE EAST OF AN EXPOSED,
WEAKLY DEFINED LLC. AN 182231Z ASCAT-C IMAGE REVEALS AN ELONGATED
CIRCULATION WITH 40-45 KNOT WINDS OVER THE EASTERN AND SOUTHERN
QUADRANTS. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
BASED ON THIS ASCAT-C IMAGE. THE INITIAL INTENSITY OF 45 KTS IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE ASCAT DATA. RECENT
SURFACE OBSERVATIONS FROM WHITEGRASS AIRPORT ON THE ISLAND OF TANNA
INDICATE SOUTHERLY WINDS AT 10 KNOTS WITH SLP NEAR 996MB. BASED
ON THE WIND SHIFT AT WHITEGRASS AIRPORT OVER THE PAST FEW HOURS, THE 
SYSTEM CENTER IS PASSING DIRECTLY OVER THE ISLAND.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: HIGH AMPLITUDE PATTERN WITH ENHANCED
STEERING FLOW BETWEEN A DEEP TROUGH AND THE SUBTROPICAL RIDGE.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   NFFN: T3.5 - 55 KTS
   CIMSS ADT: 59 KTS AT 182330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 09P IS TRACKING QUICKLY
EAST-SOUTHEASTWARD WITHIN THE ENHANCED FLOW BETWEEN A DEEP TROUGH
AND THE STR POSITIONED TO THE EAST. TC 09P WILL WEAKEN STEADILY
THROUGHOUT THE FORECAST DUE TO INCREASING VERTICAL WIND SHEAR UNDER
THE SUBTROPICAL WESTERLIES. THEREFORE, THE SYSTEM IS EXPECTED TO
TRANSITION TO A SUBTROPICAL CYCLONE WITHIN THE NEXT 36 TO 48 HOURS
AS IT ACCELERATES SOUTHEASTWARD.  

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN TIGHT
AGREEMENT LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST.
RELIABLE INTENSITY GUIDANCE ALSO SUPPORTS THE JTWC INTENSITY
FORECAST WITH MEDIUM CONFIDENCE WITH GUIDANCE INDICATING A
SHORT-TERM INCREASE FOLLOWED BY STEADY WEAKENING. 

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