WDPN34 PGTW 120300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (USAGI) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.8N 133.8E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 746 NM EAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 27W (USAGI) WITH CONVECTIVE BANDING ALONG THE WESTERN
PERIPHERY OF THE SYSTEM WRAPPING INTO THE OBSCURED LOW-LEVEL
CIRCULATION CENTER (LLCC). ENVIRONMENTAL ANALYSIS INDICATES THAT 27W
IS IN A FAVORABLE ENVIRONMENT FOR INTENSIFICATION CHARACTERIZED BY
MODERATE EQUATORWARD OUTFLOW ALOFT, LOW (10-15 KTS) VERTICAL WIND
SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE TIGHTLY
WRAPPING LOW-LEVEL CLOUD LINES IN THE ANIMATED MSI. THE INITIAL
INTENSITY OF 45 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 49 KTS AT 120000Z
   CIMSS AIDT: 40 KTS AT 120000Z
   CIMSS DPRINT: 44 KTS AT 120000Z
   CIMSS DMINT: 41 KTS AT 112148Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: 27W IS FORECAST TO CONTINUE TRACKING
WEST-NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF A STR TO THE
NORTH THROUGH TAU 48. AFTER TAU 48, THE SYSTEM WILL BEGIN TRACKING
NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE STR. NEAR TAU
72, A BIFURCATION SCENARIO BEGINS WITH TWO DISTINCT POSSIBILITIES.
THE FIRST BEING A RECURVE EAST OF TAIWAN AND THE OTHER IS A
WESTWARD TRACK INTO THE SOUTH CHINA SEA. NEAR TAU 96, A COLD SURGE
FLOWING TOWARDS TO SOUTHWEST IS THE CAUSE FOR THE WESTWARD TRACK
INTO THE SOUTH CHINA SEA. ON THE OTHER HAND, IF THE SYSTEM TRACKS
JUST QUICK ENOUGH TO OUTPACE THE ONSET OF THE COLD SURGE, A RECURVE
WILL ENSUE. THE JTWC TRACK IS PLACED CLOSER TO THE RECURVE SCENARIO
DUE TO THE EXPECTATION THAT THE VORTEX WILL REMAIN STRONG ENOUGH TO
NOT GET SHOVED SOUTHWESTWARD ALONG THE LOW-LEVEL FLOW OF THE COLD
SURGE. HOWEVER, THERE REMAINS LARGE UNCERTAINTY IN THE FORECAST AND
THE TRACK COULD SHIFT. REGARDING THE INTENSITY OF 27W, THE
ENVIRONMENT IS EXPECTED TO REMAIN CONDUCIVE OVERALL THROUGH TAU 48
WITH A PEAK INTENSITY OF 100 KTS. AFTER TAU 48, VERTICAL WIND SHEAR
WILL INCREASE AND SEA SURFACE TEMPERATURES WILL DROP. ADDITIONALLY,
THE COLD SURGE WILL BRING IN COLD AND DRY AIR TO THE SYSTEM. AS A
RESULT, 27W IS FORECAST TO QUICKLY WEAKEN TO AROUND 45 KTS AT TAU
120.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 72, HOWEVER, AS PREVIOUSLY MENTIONED, A BIFURCATION
OCCURS AFTERWARDS. GFS IS BEGINNING TO TRACK THE VORTEX FURTHER
NORTH, EAST OF TAIWAN, BUT NOW WITH A SHARP SOUTHWESTWARD TURN AT
TAU 120. ECMWF AND ITS ENSEMBLE ARE CONTINUING TO SUGGEST A
RECURVE. THE JTWC TRACK FORECAST IS PLACED CLOSE TO CONSENSUS
THROUGH TAU 72 AND CLOSER TO THE ECMWF AFTERWARDS, ALBEIT SLIGHTLY
SLOWER DUE TO THE COLD SURGE. INTENSITY GUIDANCE IS IN OVERALL
MODERATE AGREEMENT WITH INTENSIFICATION THROUGH TAU 48 AND
WEAKENING THEREAFTER. PEAK INTENSITIES RANGE FROM 80 KTS (GFS) TO
110 KTS (HWRF). 

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