WDPN31 PGTW 190300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (FENGSHEN) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.2N 121.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 38 NM SOUTHEAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS IMPROVED
BANDING WRAPPING INTO THE CONSOLIDATING LOW-LEVEL CIRCULATION CENTER 
WITH EXPANDING DEEP CONVECTION THAT HAS RECENTLY BEGUN TO CONSOLIDATE 
OVER THE WESTERN QUADRANT OFF THE COAST OF LUZON. ENVIRONMENTAL 
ANALYSIS INDICATES A MARGINALLY UNFAVORABLE ENVIRONMENT, CHARACTERIZED 
BY SIGNIFICANT TERRAIN INTERACTION OVER LUZON, OFFSET BY STRONG 
OUTFLOW, VERY WARM (29-30C) SEA SURFACE TEMPERATURES, AND LOW (5-10 
KTS) VERTICAL WIND SHEAR. TROPICAL STORM (TS) 30W (FENGSHEN) HAS 
MAINTAINED INTENSITY, DESPITE TRACKING OVER LAND FOR THE PAST 12 
HOURS. SURFACE OBSERVATIONS NEAR MANILA, PHILIPPINES SUPPORT THE 
INITIAL POSITION SOUTHEAST OF MANILA; HOWEVER, LACK OF HIGH-RESOLUTION 
MICROWAVE AND RADAR DATA WHILE THE SYSTEM IS INLAND HAS SIGNIFICANTLY 
DEGRADED THE JTWC INITIAL POSITION CONFIDENCE. THE INITIAL INTENSITY 
OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY 
DVORAK FIXES AND THE OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: THE WESTERN EXTENSION OF THE
SUBTROPICAL RIDGE (STR) TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.0 - 30 KTS
   CIMSS ADT: 39 KTS AT 182230Z
   CIMSS AIDT: 38 KTS AT 182230Z
   CIMSS D-MINT: 30 KTS AT 182311Z
   CIMSS D-PRINT: 32 KTS AT 180000Z
   CIMSS SATCON: 40 KTS AT 182200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: TERRAIN INTERACTION WITH LUZON

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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: TS 30W DOES NOT HAVE MUCH LONGER OVER LAND AND
IS EXPECTED TO REEMERGE OVER WATER PRIOR TO TAU 12. IT WILL
CONTINUE ITS NORTHWESTWARD TRAJECTORY FOR THE NEXT 36 HOURS WHILE
UNDER THE INFLUENCE OF THE EXTENSION OF THE STR TO ITS NORTH.
BEGINNING AROUND TAU 36, 30W WILL TRACK INTO A WEAKNESS IN THE
STEERING RIDGE, CAUSING IT TO SLOW WITH THE POSSIBILITY OF
QUASI-STATIONARY OR ERRATIC MOVEMENT IN THE COMPETING STEERING
ENVIRONMENT. CONCURRENT WITH THE COMPETING STEERING BETWEEN TAU
36-48, 30W WILL COLLIDE WITH A COLD SURGE FUNNELING SOUTHWESTWARD
THROUGH THE TAIWAN STRAIT, INTRODUCING SIGNIFICANT AMOUNTS OF DRY,
COOL AIR INTO THE ENVIRONMENT. AFTER TAU 48, FENGSHEN WILL
TRANSITION TO THE STEERING INFLUENCE OF A STR THAT WILL FORM AND
BUILD TO ITS NORTHWEST, CAUSING IT TO TURN SOUTHWESTWARD. 30W WILL
TRACK SOUTHWESTWARD FOR THE REMAINDER OF THE FORECAST PERIOD. AFTER
30W HAS TRACKED OVER WATER AND AWAY FROM LAND, THE ENVIRONMENT IS
EXPECTED TO BECOME FAVORABLE, ALLOWING FENGSHEN TO STEADILY
INTENSIFY WHILE TRACKING NORTHWESTWARD FOR THE NEXT 36 HOURS. 30W
WILL BRIEFLY REACH TYPHOON STRENGTH AS A RESULT OF THE ENHANCED
WINDS FROM THE COLD SURGE WITH A PEAK AT 70 KTS BETWEEN TAU 48-72.
AFTER TRANSITIONING STEERING RIDGES AND BEGINNING ITS SOUTHWESTWARD
TRACK, 30W IS FORECAST TO RAPIDLY WEAKEN FOR THE REMAINDER OF THE
FORECAST PERIOD DUE TO THE SUDDEN INUNDATION OF DRY AIR ENTRAINING
INTO THE EASTERN FLANK. 

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN STRONG
AGREEMENT IN A NORTHWESTWARD TRACK, FOLLOWED BY A BRIEF STALL AND A
SOUTHWESTWARD TURN BEFORE A SOUTHWESTWARD TRACK FOR THE REMAINDER
OF THE FORECAST PERIOD. THERE IS SOME DISAGREEMENT IN THE TIMING OF
THE STALL AND SOUTHWESTWARD CURVE, AS WELL AS TRACK SPEED FOLLOWING
THE TURN, LEADING TO A 300NM ALONG-TRACK SPREAD AT TAU 120. AS A
RESULT, THE JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE FROM
TAU 0-72, AND MEDIUM CONFIDENCE FROM TAU 72-120. RELIABLE INTENSITY
GUIDANCE IS IN GOOD AGREEMENT THAT 30W WILL STEADILY INTENSIFY
AFTER REEMERGING OVER WATER AND REACHING A PEAK BETWEEN TAU 60-72.
THE JTWC INTENSITY FORECAST LIES SLIGHTLY HIGHER THAN THE BULK OF
CONSENSUS MEMBERS WITH OVERALL MEDIUM CONFIDENCE.

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