WDPN31 PGTW 101500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (SINLAKU) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 8.1N 150.9E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 488 NM SOUTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
EXPANDING CENTRAL DENSE OVERCAST (CDO) AND A VORTEX THAT IS
BECOMING VERTICALLY ALIGNED. SINCE 100800Z AND DURING THE DIURNAL
MINIMUM, CONVECTION HAS EXPLODED OVER THE EASTERN PERIPHERY OF THE
CDO, WITH OVERSHOOTING CLOUD TOPS MEASURING -97 DEGREES CELSIUS AND
A DEFINED GRAVITY WAVE PROPAGATING THROUGH THE NORTHEAST QUADRANT.
MEANWHILE, A 100800Z WSF-M MWI PASS REVEALED A CLOSED LOWER-LEVEL
INNER CORE. A 101350Z METAR FROM CHUUK MEASURED A WIND GUST OF 48
KTS AND A MEAN SEA-LEVEL PRESSURE OF 986.8 MB. THE EXPANDING
OVERCAST IN THE UPSHEAR SIDE OF THE CIRCULATION INDICATES THAT THE
SYSTEM IS ABLE TO RESIST THE EFFECTS OF MODERATE, SOUTHEASTERLY
VERTICAL WIND SHEAR. ENVIRONMENTAL ANALYSES REVEAL FAVORABLE
CONDITIONS FOR INTENSIFICATION, CHARACTERIZED BY WARM SEA SURFACE
TEMPERATURES (SST), ABUNDANT DEEP-LAYER MOISTURE AS EVIDENCED BY
THE 101200Z CHUUK ATMOSPHERIC SOUNDING, AND ROBUST POLEWARD
OUTFLOW. WHILE A PARTIAL 101124Z ASCAT-B PASS STILL DEPICTS SOME
ASYMMETRIES IN THE SURFACE WIND FIELD, THE AFOREMENTIONED FACTORS
AND DEVELOPMENT TRENDS INDICATE THAT TS 04W IS PRIMED FOR A MORE
RAPID RATE OF INTENSIFICATION. THE INITIAL INTENSITY IS SET AT 55
KTS WITH HIGH CONFIDENCE BASED ON THE UNANIMOUS T3.5 DVORAK
ESTIMATES FROM PGTW, KNES, RJTD, AND RCTP. THE INITIAL POSITION IS
PLACED WITH LOW CONFIDENCE WITH SUPPORT FROM THE ASCAT PASS AND THE
SURFACE OBSERVATION AT CHUUK. THE MAXIMUM SIGNIFICANT WAVE HEIGHT
HAS BEEN REDUCED DUE A TEMPORARY CONTRACTION OF THE EXTENT OF
GALE-FORCE WINDS OVER THE NORTHERN SEMICIRCLE AS THE SYSTEM WORKS
OUT ITS ASYMMETRIES.

INITIAL WIND RADII BASIS: PARTIAL SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT WITH A
NEAR-EQUATORIAL RIDGE (NER) TO THE EAST AND A STRONG SUBTROPICAL
RIDGE (STR) TO THE NORTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 55 KTS AT 101140Z
   CIMSS AIDT: 45 KTS AT 101140Z
   CIMSS D-MINT: 45 KTS AT 100800Z
   CIMSS D-PRINT: 54 KTS AT 101140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: LOCATED WITHIN A VERY WEAK STEERING
ENVIRONMENT WITH A NER TO THE EAST AND A STRONG STR TO THE
NORTHWEST, TS 04W IS QUASISTATIONARY WITH AN ESTIMATED WESTWARD
MOTION OF 2-3 KTS OVER THE PAST 12 HOURS. A TURN TOWARDS THE
NORTH-NORTHWEST IS ANTICIPATED OVER THE NEXT 12-18 HOURS AS THE NER
STRENGTHENS. AS THIS HAPPENS, THE STR WILL WEAKEN AND RETREAT
WESTWARD, WHICH WILL INDUCE A FASTER RATE OF TRAVEL TOWARDS THE
NORTHWEST FOR THE REMAINDER OF THE FORECAST PERIOD. TS 04W WILL
MAKE A DANGEROUSLY CLOSE APPROACH TO GUAM, AND IT APPEARS
INCREASINGLY LIKELY TO PASS SOUTH OF GUAM OR OVER THE SOUTHERN TIP.
HOWEVER, THE MORE NORTHERN ISLANDS OF ROTA, TINIAN, AND SAIPAN ARE
WITHIN THE UNCERTAINTY ENVELOPE. WARM SST, PLENTIFUL MID-LEVEL
MOISTURE, AND MODEST UPPER-LEVEL DIVERGENCE WILL FUEL CONTINUED
INTENSIFICATION AS TS 04W APPROACHES THE MARIANA ISLANDS. WITH
IMPROVING CONVECTIVE STRUCTURE, THE FORECAST CALLS FOR A
CLIMATOLOGICAL RATE OF DEVELOPMENT FOR THE FIRST 12 HOURS AND
EXPLICIT RI FROM TAU 12 TO TAU 48, ENABLING THE STORM TO REACH AT
LEAST 115 KTS AT TAU 72. AFTER PASSING GUAM, INTERNAL STRUCTURAL
CHANGES SUCH AS AN EYEWALL REPLACEMENT CYCLE AND AN EXPANSION OF
THE EYE WILL LIMIT FURTHER DEVELOPMENT.

MODEL DISCUSSION: WHILE THE CROSS-TRACK SPREAD REMAINS LARGE AT TAU
72, THE UNCERTAINTY ENVELOPE IS SLOWLY SHRINKING. THE GFS, GEFS
MEAN, AND ECMWF TRACKERS HAVE SHIFTED NORTHWARD AND CLOSER TO GUAM,
AND THE EXPERIMENTAL AI MODELS HAVE SIMILARLY SHIFTED CLOSER TO
GUAM BUT FROM THE OTHER END. THE TRACK FORECAST FOLLOWS THE ECMWF
AND THE MULTI-MODEL CONSENSUS THROUGH TAU 72, AFTER WHICH TIME THE
TRACK IS SLIGHTLY HEDGED TOWARDS THE AI MODELS. WHILE THE CONSENSUS
OF THE RELIABLE MODEL GUIDANCE INDICATES A LANDFALL OVER GUAM, A
SMALL SHIFT IN THE TRACK WOULD NONETHELESS BRING WIDESPREAD IMPACTS
TO THE MARIANA ISLANDS, GIVEN THE SYSTEM'S LARGE WIND FIELD.
MULTIPLE RI AIDS HAVE TRIGGERED, WHICH INCREASES THE CONFIDENCE
THAT A MORE SUBSTANTIAL RATE OF INTENSIFICATION WILL SOON COME TO
FRUITION. THE AI-RI PRODUCT FROM CIMSS INDICATES A SUBSTANTIAL
PROBABILITY OF RI, GIVING A GREATER THAN 50 PERCENT CHANCE OF A 45
KT INCREASE IN THE NEXT 36 HOURS AND A 40 PERCENT CHANCE OF A 65 KT
INCREASE IN THE NEXT 72 HOURS. THE FORECAST INTENSITY FOLLOWS THE
CLIMATOLOGICAL RATE THROUGH TAU 12 AND IS THEN ALIGNED MORE CLOSELY
TO HAFS-A FROM TAU 12 TO TAU 48. THE 115 KT PEAK IS AT THE UPPER
END OF THE INTENSITY GUIDANCE BUT IS BELOW THE 125 KT PEAK FROM
HAFS-A.

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