WDPN31 PGTW 021500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (YAGI)         
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.2N 122.0E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 166 NM NORTH-NORTHEAST OF MANILA,
                         PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 08 KTS

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 12W MADE LANDFALL AROUND 020600Z AND HAS
TRACKED FURTHER INLAND OVER THE MOUNTAINOUS TERRAIN OF LUZON OVER
THE PAST SIX HOURS. AS DEPICTED IN ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY AND RADAR IMAGERY, TS 12W HAS BECOME INCREASINGLY
DISORGANIZED, WITH MORE FRAGMENTED CORE CONVECTION AND WARMING
CLOUD TOP TEMPERATURES. THE LOW-LEVEL CIRCULATION CENTER (LLCC) HAS
BEEN DIFFICULT TO PINPOINT BUT IS BASED ON A 021020Z SSMIS 91GHZ
MICROWAVE IMAGE, WHICH SHOWS CURVED CONVECTIVE BANDING OVER THE
SOUTHERN QUADRANT WRAPPING INTO A WEAK LLCC. SURFACE OBSERVATIONS
FROM TUGUEGARAO (98233), LOCATED ABOUT 28NM NW OF THE CENTER, ALSO
SUPPORT THE INITIAL POSITION, WITH NNE SURFACE WINDS AT 10 KNOTS.
THE LATEST OBSERVATIONS INDICATE THEIR WINDS SHIFTING TO A
SOUTHEASTERLY DIRECTION AS THE CENTER SLIPPED TO THE SOUTHWEST. THE
INITIAL INTENSITY IS ASSESSED AT 40 KNOTS, CONSERVATIVELY, WITH LOW
CONFIDENCE AND VERY LITTLE SUPPORTING EVIDENCE.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGING TO THE
EAST AND NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: LAND INTERACTION

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 12W IS GRADUALLY TURNING NORTHWESTWARD AS
IT SLOWLY TRANSITIONS TO THE STEERING INFLUENCE OF A STRONG
SUBTROPICAL RIDGE ENTRENCHED OVER EASTERN CHINA. TRACK SPEEDS ARE
EXPECTED TO SLOW AS IT TRANSITIONS DUE TO THE WEAKER STEERING
ENVIRONMENT BETWEEN THE TWO SUBTROPICAL RIDGES. THE SYSTEM IS
FORECAST TO WEAKEN SLIGHTLY OVER THE NEXT 12 HOURS AS IT TRANSITS
NORTHERN LUZON. AFTER TAU 12, THE SYSTEM WILL STRENGTHEN STEADILY
AS IT TURNS WESTWARD AND ACCELERATES AWAY FROM LUZON. ENVIRONMENTAL
CONDITIONS WILL BECOME INCREASINGLY FAVORABLE FOR RAPID
INTENSIFICATION (RI) AFTER TAU 24, WITH WARM SSTS OF 30-31C, LOW
VWS OF LESS THAN 10 KTS, STRONG EQUATORWARD OUTFLOW INTO THE TEJ,
AND IMPROVED POLEWARD VENTING INTO A STRENGTHENING TUTT TO THE
NORTHEAST. RI SHOULD CONTINUE THROUGH TAU 84, WITH A PEAK INTENSITY
OF ABOUT 115 KNOTS. AFTER TAU 84, THE SYSTEM WILL GRADUALLY WEAKEN
AS IT APPROACHES HAINAN ISLAND DUE TO INCREASING FRICTIONAL
EFFECTS.  

MODEL DISCUSSION: MESOSCALE MODELS CONTINUE TO SUPPORT A SUSTAINED
PERIOD OF RI AFTER TAU 24, WITH HAFS-A SHOWING A PEAK OF 130 KNOTS
AND COAMPS-TC (GFS INITIAL BOUNDARY CONDITIONS) PEAKING AT 125
KNOTS. ADDITIONALLY, THE 020000Z COAMPS-TC ENSEMBLE (CTCXEPS)
INTENSITY PROBABILITY PRODUCT SHOWS PEAK 50-60 PERCENT PROBABILITY
OF RI VALUES IN THE TAU 42 TO TAU 66 TIME FRAME. DUE TO THE
FAVORABLE ENVIRONMENT AND ROBUST OUTFLOW ANTICIPATED OVER THE SOUTH
CHINA SEA, THE JTWC FORECAST IS PLACED SIGNIFICANTLY HIGHER THAN
THE INTENSITY CONSENSUS (ICNW) WITH MEDIUM CONFIDENCE. AS FAR AS
TRACK CONFIDENCE, BOTH THE 020000Z ECMWF ENSEMBLE (EPS) AND 020600Z
GFS ENSEMBLE (GEFS) REVEAL A TIGHT GROUPING OF ALL SOLUTIONS TRACKING 
THE SYSTEM TOWARD HAINAN ISLAND, WITH SOME MODERATE UNCERTAINTY IN
THE LANDFALL LOCATION FROM CENTRAL VIETNAM TO THE SOUTHERN CHINA
COAST. DETERMINISTIC GUIDANCE HAS COME IN BETTER AGREEMENT AND
SHOWS A NARROWER SPREAD OF TRACKERS FROM SOUTHERN HAINAN ISLAND TO
THE SOUTHERN CHINA COAST, WITH A 175 TO 200NM CROSS-TRACK SPREAD
AT TAU 120.       

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