WDPN32 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (PODUL) WARNING NR 
011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.5N 141.0E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 199 NM SOUTH OF IWO TO
   MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS DEEP
CONVECTION OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC) OF
TROPICAL STORM (TS) 16W. WATER VAPOR IMAGERY REVEALS DRY AIR TO THE
NORTH AND WEST OF THE DEEP CONVECTION. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON A 091200Z METOP-B ASCAT
PARTIAL IMAGE REVEALING THE WESTERN PORTION OF THE LOW-LEVEL
CIRCULATION CENTER. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED PARTIAL
SCATTEROMETRY AND AN EARLIER 090841Z RCM-3 SYNTHETIC APERTURE RADAR
(SAR) IMAGE REVEALING THE STRONGEST WINDS IN THE EASTERN PERIPHERY
OF THE LLCC. THERE IS SLIGHT UNCERTAINTY IN THE PEAK INTENSITIES OF
THE SAR IMAGE, WITH SOME POTENTIALLY EXTRANEOUSLY HIGH INTENSITIES
DUE TO ICE CONTAMINATION.  THE AGENCY AND OBJECTIVE FIXES ARE
SPREAD BETWEEN 3.0-4.0, BUT THE INTENSITY IS ANALYZED AT 50KTS.

INITIAL WIND RADII BASIS: 090841Z RCM-3 SAR DATA 

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE CENTERED OVER THE
EAST CHINA SEA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 50 KTS AT 091200Z
   CIMSS ADT: 47 KTS AT 091130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL STORM 16W WILL INITIALLY MOVE
WESTWARD FOR 48 HOURS, STEERED BY A RIDGE TO THE NORTH, BEFORE
CURVING NORTHWESTWARD AFTER TAU 72. THE STORM IS FORECAST TO
INTENSIFY TO A PEAK OF 70 KNOTS AFTER 36 HOURS, BENEFITING FROM
FAVORABLE CONDITIONS LIKE WARM SEA SURFACE TEMPERATURES AND
MODERATE EASTERLY UPPER-LEVEL DIVERGENCE. HOWEVER, THE STRENGTH OF
TS 16W WILL BE CHALLENGED BY TWO KEY FACTORS. INITIALLY, MARGINAL
VERTICAL WIND SHEAR (20-25 KNOTS) WILL LIMIT THE RATE OF
DEVELOPMENT. THEN, AFTER 36 HOURS, VERTICAL WIND SHEAR WILL BECOME
HIGHLY UNFAVORABLE (30-35 KNOTS) AS THE SYSTEM ENCOUNTERS ENHANCED
EASTERLY FLOW OF A BUILDING UPPER-LEVEL RIDGE. THIS INCREASED
SHEAR, ALONG WITH MID-LEVEL DRY AIR, WILL CAUSE THE STORM TO
GRADUALLY WEAKEN TO 30 KNOTS BY THE END OF THE FORECAST, JUST AFTER
MAKING LANDFALL IN MAINLAND CHINA.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT TS 16W WILL BE DRIVEN WESTWARD, AND THEN NORTHWESTWARD WHILE
UNDER THE STEERING INFLUENCE OF A SUBTROPICAL RIDGE TO THE NORTH.
THERE ARE VARIATIONS IN THE STRENGTH AND HOW FAR SOUTH THE RIDGE
EXTENDS, AND THE SLIGHT VARIATIONS OF TRACK SOLUTIONS ARE CLOSELY
ASSOCIATED WITH THE SPREAD OF JTWC INTENSITY GUIDANCE. THE
CROSS-TRACK SPREAD AT TAU 72 IS 295NM, AND THE CROSS-TRACK SPREAD
AT TAU 120 IS 580NM. THE JTWC TRACK FORECAST LIES NORTH OF THE
CONSENSUS MEAN. HOWEVER, THE LAST FEW MODEL RUNS HAVE TRENDED
SOUTHWARD. THE INTENSITY GUIDANCE IS SIGNIFICANTLY SPREAD, WITH
COAMPS-TC SOLUTIONS EXTREMELY HIGH BETWEEN 95-140KTS, AND A TIGHTER
GROUPING OF HAFS-A, GFS, AND JTWC SHIPS GUIDANCE BETWEEN 55-70KTS
IS CLOSER TO THE CONSENSUS MEAN. IF THE SYSTEM TRACKS FARTHER
NORTH, THE DRY AIR AND SHEAR WILL HAVE A STRONGER EFFECT THAN IF TS
16W TRACKS SOUTH. THE JTWC INTENSITY FORECAST LIES SLIGHTLY NORTH
OF THE MULTI-MODEL INTENSITY CONSENSUS.

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