WDPN31 PGTW 120900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (WUTIP) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.2N 109.9E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 117 NM NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 01W (WUTIP) WITH EXPOSED LOW-LEVEL CLOUD LINES TIGHTLY
WRAPPING INTO AN OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC) SOUTH
OF HAINAN. 120540Z AMSR2 MICROWAVE IMAGES REVEALED THAT THE LLCC IS
OFFSET SLIGHTLY TO THE NORTHEAST OF THE BULK OF CONVECTION.
ENVIRONMENTAL ANALYSIS INDICATES THAT 01W IS IN A MARGINALLY
FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE EQUATORWARD OUTFLOW
ALOFT, MODERATE (15-20 KTS) EAST-NORTHEASTERLY VERTICAL WIND SHEAR,
AND WARM (29-30 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION
IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE 120540Z AMSR2 37 GHZ
MICROWAVE IMAGE. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE 120229Z METOP-B ASCAT PASS SHOWING A
PATCH OF 45 KNOT SOUTHWESTERLIES WITHIN THE SOUTHERN SEMICIRCLE.
ADDITIONALLY, A MAJORITY OF AGENCY DVORAK FIXES OF T3.0 SUPPORT THE
INITIAL INTENSITY ASSESSMENT. CIMSS OBJECTIVE INTENSITY ESTIMATES
ARE A BIT LOWER, HOVERING AROUND 37-41 KTS.

INITIAL WIND RADII BASIS: 120229Z METOP-B SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 37 KTS AT 120600Z
   CIMSS AIDT: 37 KTS AT 120600Z
   CIMSS DPRINT: 41 KTS AT 120600Z
   CIMSS DMINT: 40 KTS AT 120543Z

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

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: 01W IS FORECAST TO TRACK NORTHWESTWARD THROUGH
TAU 12 BEFORE BEGINNING TO ROUND THE RIDGE AXIS WITH A NORTHWARD
TURN. AN INITIAL LANDFALL, JUST AFTER TAU 12, IS FORECAST TO OCCUR
ALONG THE SOUTHWESTERN COAST OF HAINAN. NEAR TAU 24, THE SYSTEM
WILL BEGIN TO TURN NORTHWESTWARD AND TRACK TOWARD THE LEIZHOU
PENINSULA. 01W IS THEN FORECAST TO MAKE A SECOND LANDFALL NEAR TAU
48 AND CONTINUE ON A NORTHWESTWARD TRACK FURTHER INLAND THROUGH
TAU 72 AS THE VORTEX DISSIPATES NORTH OF HONG KONG. 01W IS FORECAST
TO MAINTAIN ITS CURRENT INTENSITY OF 50 KTS THROUGH TAU 24 DUE TO
THE MOSTLY FAVORABLE ENVIRONMENT BEFORE LANDFALL. AFTER TAU 24,
TERRAIN INTERACTION WITH HAINAN WILL WEAKEN THE VORTEX AS IT
APPROACHES THE COAST OF CHINA. AFTER TAU 48, SIGNIFICANT TERRAIN
INTERACTION WITH MAINLAND CHINA WILL CAUSE 01W TO QUICKLY WEAKEN
AND DISSIPATE BY TAU 72.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH A MERE 35 NM CROSS-TRACK SPREAD AND 50 NM
ALONG-TRACK SPREAD AT TAU 48. AT TAU 72, ALONG-TRACK SPREAD
INCREASES TO 230 NM DUE TO THE WEAK NATURE OF THE VORTEX AND RAPID
DISSIPATION. OVERALL, THE JTWC TRACK FORECAST IS PLACED WITH HIGH
CONFIDENCE, CLOSE TO THE MULTI-MODEL CONSENSUS. INTENSITY GUIDANCE
IS IN MODERATE AGREEMENT, WITH MODELS RANGING FROM 40-50 KTS
THROUGH TAU 48 AND THEN AGREE ON RAPID WEAKENING AFTERWARD. THE
JTWC INTENSITY FORECAST IS PLACED WITH MEDIUM CONFIDENCE AS A
RESULT.

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