WDPN31 PGTW 292100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (FOUR) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.1N 114.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 361 NM WEST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A BROAD
AREA OF BUILDING CONVECTION IN THE SOUTHERN SEMI-CIRCLE OF AN
ASSESSED LOW LEVEL CIRCULATION CENTER (LLCC). A 291314Z ASCAT-C AND
A 291401Z ASCAT-B BOTH SHOW A WELL DEFINED LLCC WITH 25 KNOTS
PREVALENT IN THE WESTERN AND SOUTHERN QUADRANTS. THE LATEST
INFRARED SATELLITE ANIMATION INDICATES THE UPPER AND MID-LEVEL
TURNING HAS BECOME CONSISTENT AND UNIFORM OVER THE PAST 5 HOURS.
THE 850MB VORTICITY SIGNATURE HAS BECOME MORE SYMMETRICAL AND
SHOWING SIGNS OF STRENGTHENING OVER THE PAST 12 HOURS. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED
ASCAT PASSES. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE ASCAT PASSES AND OVER ALL STRUCTURE. 
INTENSITY IS ALIGNED WITH THE PGTW DVORAK ESTIMATE OF 2.0, AND 
SLIGHTLY HIGHER THAN RJTD AND KNES WHICH ARE AT 1.5.

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

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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: TD 04W WILL TRACK NORTH-NORTHWESTWARD AND
STRENGTHEN TO 35 KTS OVER THE NEXT 24 HOURS. BY TAU 36, THE STR
TO THE NORTHEAST WILL BUILD CAUSING THE SYSTEM TO SHIFT TO A MORE
NORTHWESTWARD TRACK. AT THIS TIME INTENSITY WILL INCREASE TO 40
KTS DUE TO TD 04W PASSING UNDER AN AREA OF DECREASED VERTICAL
WIND SHEAR (5-10KTS) AND CONTINUE TO INCREASE IN INTENSITY TO 50 
KNOTS BY TAU 48, JUST BEFORE LANDFALL OVER THE ISLAND OF HAINAN. BY 
TAU 72, TD 04W WILL SUCCUMB TO THE AFFECTS OF LAND INTERACTION 
BETWEEN HAINAN AND MAINLAND CHINA AND WILL DECREASE IN INTENSITY TO 
40 KTS. TAUS 96 AND 120 TAKE THE SYSTEM OVER LAND IN SOUTHERN CHINA 
WHERE DISSIPATION WILL OCCUR.

MODEL DISCUSSION: THE JTWC MODEL CONSENSUS ENVELOPE IS RELATIVELY
UNIFORM. THERE IS A 50 NM SPREAD IN TRACK CONSENSUS AT TAU 12,
INCREASING TO 74 NM BY TAU 48. AFTER THE SYSTEM INTERACTS WITH LAND
BY TAU 72, THE MODEL SPREAD INCREASES TO 150 NM, LOWERING THE
CONFIDENCE IN THE TRACK FORECAST DURING THE LATER PORTION OF THE 
FORECAST PERIOD. INTENSITY GUIDANCE ALSO IS RELATIVELY UNIFORM. THE 
JTWC FORECAST INTENSITY IS PLACED WITH MEDIUM CONFIDENCE. ALL AGREE 
ON INCREASING INTENSITY UP TO TAU 48. AFTERWARDS, THE JTWC INTENSITY
IS SET BELOW CONSENSUS TO ACCOUNT FOR A GREAT DEAL OF LAND
INTERACTION WITH HAINAN AND MAINLAND CHINA.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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