WDPS32 PGTW 062100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11P (ELEVEN)    WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.7S 170.5W
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 97 NM NORTH OF PAGO PAGO
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 18 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT,
CONSOLIDATING (VERY SMALL) SYSTEM WITH EXPOSED LOW-LEVEL CLOUD
LINES FEEDING INTO THE SOUTHWESTERN FLANK OF THE CORE CONVECTION,
WHICH IS WELL ORGANIZED. TROPICAL CYCLONE (TC) 11P HAS FORMED
RAPIDLY WITHIN THE SOUTH PACIFIC CONVERGENCE ZONE, WITH EXTENSIVE
NEAR GALE-FORCE WESTERLIES PERSISTING ALONG THE NORTHERN PERIPHERY
OF THE SPCZ OVER THE PAST FEW DAYS. RECENT WINDSPEED DATA INCLUDING
A 061706Z SMAP IMAGE FROM REMSS INDICATES GALE-FORCE WINDS OVER THE
NORTHERN SEMICIRCLE WITH 20-25 KNOT WINDS OVER THE SOUTHERN
SEMICIRCLE. RECENT MICROWAVE IMAGERY INCLUDING A 061715Z SSMIS 91
GHZ MICROWAVE IMAGE DEPICT CURVED DEEP CONVECTIVE BANDING OVER THE
NORTHERN SEMICIRCLE WRAPPING INTO THE CONSOLIDATING LOW-LEVEL
CIRCULATION. THE SSMIS IMAGE SHOWS SPARSE CONVECTION OVER THE
SOUTHERN SEMICIRCLE AT THIS TIME. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON THE SSMIS IMAGE AND THE MSI.
UPPER-LEVEL CONDITIONS HAVE CLEARLY IMPROVED OVER THE PAST 12
HOURS, WITH NEAR RADIAL OUTFLOW AND ENHANCED POLEWARD OUTFLOW INTO
THE SUBTROPICAL JET TO THE SOUTH. THE INITIAL INTENSITY IS ASSESSED
AT 30 KNOTS BASED ON THE CONVECTIVE STRUCTURE AND THE PGTW
SUBJECTIVE DVORAK ESTIMATE OF T2.0 (30 KNOTS).

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE (NER) ENTRENCHED
TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 11P IS FORECASTED TO TRACK
SOUTHEASTWARD THROUGH TAU 24 ALONG THE SOUTHERN PERIPHERY OF THE
NER BUT IS EXPECTED TO TURN SOUTHWARD AND SLOW AS IT ENCOUNTERS A
BROAD LOW-LEVEL HIGH POSITIONED TO THE SOUTH. THIS HIGH WILL EFFECTIVELY
BLOCK POLEWARD PROGRESSION AND STEER THE SYSTEM SLOWLY WESTWARD BY TAU 72.
TC 11P WILL CONTINUE TO INTENSIFY THROUGH TAU 24 DUE TO ROBUST POLEWARD
OUTFLOW INTO THE SUBTROPICAL JET AND WARM SST
(30-31 C) VALUES. THE PEAK INTENSITY WILL OCCUR NEAR TAU 24 AT 40
KNOTS. AFTER TAU 24, THE SYSTEM WILL APPROACH THE NORTHEAST
PERIPHERY OF A STRONG UPPER-LEVEL LOW, WHICH WILL LEAD TO A STEADY
WEAKENING TREND, WITH INCREASING VERTICAL WIND SHEAR (30-40 KNOTS).
AS THE SYSTEM STALLS AFTER TAU 48, THE STRONG UPPER-LEVEL LOW AND
ITS ASSOCIATED TROUGH WILL SHIFT SOUTH OF THE SYSTEM, WHICH WILL
ACCELERATE THE WEAKENING TREND AND LEAD TO DISSIPATION BY TAU 72.  
    
MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM, NUMERICAL MODEL
GUIDANCE IS IN TIGHT AGREEMENT THROUGH TAU 24 DIVERGING
SIGNIFICANTLY THROUGH THE REMAINDER OF THE FORECAST PERIOD. THE
061200Z GFS ENSEMBLE (GEFS) REVEALS A SIMILAR SPREAD OF SOLUTIONS
WITH A SQUASHED SPIDER PATTERN AFTER TAU 24, WITH SOLUTIONS FANNING
OUT. THE BULK OF THE SOLUTIONS TURN THE SYSTEM WESTWARD AFTER TAU
48, WHICH FITS WITH THE JTWC TRACK FORECAST PHILOSOPHY.     

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