WDPN31 PGTW 180300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 30W (FENGSHEN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.6N 125.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 305 NM EAST-SOUTHEAST OF MANILA,
   PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A 
CONSOLIDATING SYSTEM, WITH EXPANDING CORE CONVECTION OBSCURING THE
LOW-LEVEL CIRCULATION CENTER (LLCC). A 172156Z WSF-M 37GHZ COLOR
COMPOSITE MICROWAVE IMAGE REVEALS A WEAKLY-DEFINED LLCC, WITH THE
BULK OF THE DEEP CONVECTION OVER THE EASTERN SEMICIRCLE, ASSOCIATED
WITH STRONG LOW-LEVEL CONVERGENT FLOW. A FORTUITOUS 180054Z ASCAT-C
IMAGE SHOWS A WELL-DEFINED CENTER, WITH 30-35 KNOT WINDS OVER THE
SOUTHERN QUADRANT, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH
CONFIDENCE. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON ASCAT-C DATA AND THE LOWER RANGE OF INTENSITY
ESTIMATES. OVERALL, ENVIRONMENTAL CONDITIONS ARE FAVORABLE WITH 
RADIAL OUTFLOW, LOW VERTICAL WIND SHEAR, WARM SST VALUES (29-30C)
AND EXTREMELY HIGH OCEAN HEAT CONTENT.

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

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
POSITIONED TO THE EAST AND NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T3.0 - 45 KTS
   CIMSS D-PRINT: 31 KTS AT 180200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 30W IS FORECAST TO
TRACK NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE LOW- TO
MID-LEVEL SUBTROPICAL RIDGE (STR) THROUGH TAU 36 SKIRTING THE
EASTERN COAST OF THE PHILIPPINE ISLANDS. DESPITE MINIMAL LAND
INTERACTION, TD 30W WILL INTENSIFY QUICKLY TO A PEAK INTENSITY OF
55 KNOTS BY TAU 24 DUE TO THE FAVORABLE CONDITIONS. AFTER MAKING
LANDFALL OVER LUZON NEAR TAU 24, THE SYSTEM WILL TURN WEST-
NORTHWESTWARD UNDER THE STEERING INFLUENCE OF THE STR TO THE
NORTH WITH SIGNIFICANT WEAKENING. THE SYSTEM IS FORECAST TO
REINTENSIFY AFTER TAU 48 TO A PEAK INTENSITY OF 70 KNOTS BY TAU 96.
STEERING DURING THIS TIMEFRAME WILL WEAKEN WITH A SLOW, ERRATIC
TRACK HIGHLY LIKELY. INTERACTION WITH A STRONG NORTHEAST SURGE
EVENT AFTER TAU 96 WILL RESULT IN A GRADUAL WEAKENING TREND AND
SHARP TURN SOUTHWESTWARD. FORECAST WIND RADII EXPAND SIGNIFICANTLY
AS THE SYSTEM'S WINDFIELD MERGES WITH THE NORTHEAST SURGE FLOW.    
     
MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN FAIR
AGREEMENT SUPPORTING THE JTWC TRACK FORECAST WITH MEDIUM
CONFIDENCE. RELIABLE INTENSITY GUIDANCE SUPPORTS A NEAR RAPID
INTENSIFICATION RATE THROUGH TAU 24 BUT IS HIGHLY DEPENDENT ON THE
EXACT TRACK FORECAST AND LAND INTERACTION. RAPID INTENSIFICATION
(RI) GUIDANCE IS TRIGGERED SUGGESTING RI IS POSSIBLE IF THE SYSTEM
TRACKS A BIT FURTHER EAST OVER THE DEEP WARM WATER.    

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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