WDPN31 PGTW 221500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 19W (NINETEEN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.8N 119.3E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 165 NM NORTHWEST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 25 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
THE LOW LEVEL CIRCULATION CENTER (LLCC) NOW ASSOCIATED WITH
TROPICAL DEPRESSION (TD) 19W HAS RAPIDLY JUMPED FROM THE EASTERN
COAST OF LUZON TO THE WEST AND REFORMED OVER THE VERY WARM WATERS
OF THE SOUTH CHINA SEA.  ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS DISORGANIZED AREAS OF DEEP CONVECTION ON THE
WESTERN EDGE OF THE LLCC, WHILE WEAKER AREAS OF CONVECTION ARE
PRESENT ALONG THE WEST COAST OF LUZON. A 221231Z ASCAT-B PASS
PROVIDED VERY TIMELY SUPPORT TO BOTH PLACEMENT OF THE LLCC AND
INSIGHTS INTO THE STRUCTURE OF THE LOWER-LEVEL WIND FIELD. THE
SCATTEROMETER DATA SHOWS A VERY LARGE FIELD OF 20 KNOT WINDS
EXTENDING FAR INTO THE LUZON STRAIT AND AS FAR SOUTH AS SUBIC BAY,
AND 25-30 KNOT WINDS EXTENDING FROM NORTHWEST OF THE LLCC AND
WRAPPING ALONG THE SOUTHERN FLANK OF THE LLCC TO NEAR THE COAST AT
IBA. THE INITIAL POSITION AND INTENSITY WERE BOTH ASSESSED WITH
HIGH CONFIDENCE BASED ON THE ASCAT-B PASS, AND IN AGREEMENT WITH
THE LIMITED AGENCY DVORAK CURRENT INTENSITY ESTIMATES NOTED BELOW.
ANIMATED WATER VAPOR IMAGERY INDICATES AN UPPER-LEVEL ANTI-CYCLONE
POSITIONED JUST SOUTH OF TAIWAN, WHICH IS IMPARTING UPPER-LEVEL
NORTHEASTERLY FLOW OVER TOP OF TD 19W. ENVIRONMENTAL CONDITIONS ARE
FAVORABLE, WITH WARM TO VERY WARM SSTS, MODERATELY HIGH OHC,
MODERATE WESTWARD OUTFLOW AND LOW EASTERLY SHEAR.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.0 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD
   OTHER FACTORS: WEAK EQUATORWARD OUTFLOW. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TD 19W IS FORECAST TO BE STRAIGHT-RUNNER TYPE
SYSTEM, MOVING STEADILY WESTWARD THROUGH THE FORECAST PERIOD, ALONG
THE SOUTHERN PERIPHERY OF A LARGE STR CENTERED OVER JAPAN. A BRIEF
SLOWDOWN IN THE TRACK SPEED IS EXPECTED AROUND TAU 48, AS THE RIDGE
AXIS RETREATS POLEWARD AND SLACKENS THE STEERING GRADIENT A NOTCH.
THE SYSTEM IS FORECAST TO SKIRT THE SOUTHERN COAST OF HAINAN ISLAND
AROUND TAU 48 AND MAKE LANDFALL ALONG THE NORTH-CENTRAL COAST OF
VIETNAM NEAR TAU 72.  IN TERMS OF INTENSITY, THE SYSTEM IS RAPIDLY
CONSOLIDATING AS EVIDENCED BY THE RECENT ASCAT DATA, EVEN IN THE
FACE OF PERSISTENT EASTERLY SHEAR. NO SIGNIFICANT CHANGES TO THE
ENVIRONMENTAL CONDITIONS ARE EXPECTED OVER THE COURSE OF THE
FORECAST. IN FACT, THE 200MB ANTI-CYCLONE CURRENTLY SOUTH OF TAIWAN
IS FORECAST TO MOVE WESTWARD AT ROUGHLY THE SAME SPEED AS TD 19W,
AND THUS REMAIN IN THE SAME RELATIVE POSITION THOUGH MOST OF THE
FORECAST. SO, THE SYSTEM WILL HAVE TO CONTEND WITH PERSISTENT
EASTERLY FLOW ALOFT, BUT SHEAR VALUES ARE FORECAST TO REMAIN IN THE
LOW TO MODERATE RANGE AND ALL GLOBAL AND MESOSCALE MODELS INDICATE
THE SYSTEM WILL BE ABLE TO FEND OFF THE WORST OF THE IMPACTS FROM
THE SHEAR. TD 19W IS FORECAST TO STEADILY INTENSIFY UP TO TYPHOON
STRENGTH PRIOR TO REACHING HAINAN ISLAND. THE FORECAST POINTS LIMIT
THE ABILITY TO DEPICT THE TRUE PEAK OF THE SYSTEM, WHICH IS
FORECAST TO OCCUR BETWEEN TAU 48 AND TAU 60, PRIOR TO LANDFALL IN
VIETNAM, AND BE BETWEEN 75-80 KNOTS. ONCE THE SYSTEM MOVES ASHORE
IN VIETNAM IT WILL RAPIDLY WEAKEN AND DISSIPATE OVER NORTHERN LAOS
BY TAU 96. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE GUIDANCE ARE ALL IN
TIGHT AGREEMENT ON THE OVERALL TRACK SCENARIO, WITH THE
DETERMINISTIC MODEL ENVELOPE JUST 70NM WIDE FROM TAU 24 THROUGH
LANDFALL. BOTH THE ECENS AND GEFS ENSEMBLE MEMBERS ARE SIMILARLY
CONSTRAINED WITH JUST A SLIGHTLY WIDER ENVELOPE. THE JTWC FORECAST
IS PLACED JUST NORTH OF THE CONSENSUS MEAN THROUGH THE FORECAST
PERIOD, WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS A BIT MORE
UNCERTAIN, WITH A BROADER RANGE OF POSSIBLE OUTCOMES. THE
DECAY-SHIPS (GFS), GFS DETERMINISTIC AND COAMPS-TC (GFS) ARE THE
MOST AGGRESSIVE MODELS, BRINGING THE PEAK UP TO 80-85 KNOTS BY TAU
72. THE HAFS-A AND DECAY-SHIPS (NAVGEM) ON THE OTHER HAND ARE
BEARISH ON THE SYSTEM, FORECASTING A PEAK OF JUST 50 KNOTS AT TAU
72. ADDITIONALLY, THE RIDE RAPID INTENSIFICATION (RI) AID HAS
TRIPPED, WHICH REACHES A PEAK OF 95 KNOTS WITHIN 48 HOURS. OTHER RI
GUIDANCE IS SHOWING SIGNIFICANT PROBABILITIES (EXCEEDING 50
PERCENT) OF INTENSIFICATION RATES AS HIGH AS 65 KNOTS IN 72 HOURS.
WHILE NOT CURRENTLY EXPECTED DUE TO THE LIMITATIONS OF THE
PERSISTENT EASTERLY SHEAR, THERE REMAINS A MODERATE CHANCE OF
SIGNIFICANT RI, ESPECIALLY IF THE SYSTEM CAN CONTINUE TO QUICKLY
ORGANIZE IN THE NEAR-TERM. 

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