WDPN31 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (YAGI) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.6N 123.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 128 NM EAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM 12W (YAGI) WITH A SYMMETRICAL CENTRAL DENSE OVERCAST (CDO)
OBSCURING THE LOW-LEVEL CIRCULATION CENTER. THE CONVECTIVE BANDING
THAT WAS ONCE PROMINENT IS NOW FADING AWAY, LEAVING THE COMPACT CDO
AS THE MAIN FEATURE OF THE STORM. ENVIRONMENTAL ANALYSIS INDICATES
THAT 12W IS CURRENTLY IN A MARGINALLY FAVORABLE ENVIRONMENT FOR
FURTHER DEVELOPMENT. VERY WARM SEA SURFACE TEMPERATURES, LOW TO
MODERATE NORTHEASTERLY VERTICAL WIND SHEAR, AND STRONG EQUATORWARD
OUTFLOW ALOFT ARE OFFSET BY TERRAIN INTERACTION WITH THE
PHILIPPINES. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
BASED ON THE ANIMATED EIR IMAGERY SHOWING THE MOSTLY OBSCURED LLCC.
THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES LISTED
BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYERED
SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 36 KTS AT 011800Z
   CIMSS ADT: 33 KTS AT 011800Z
   CIMSS AIDT: 32 KTS AT 011800Z
   CIMSS DPRINT: 35 KTS AT 011800Z
   CIMSS DMINT: 36 KTS AT 011729Z
   

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: TERRAIN INTERACTION ON THE WESTERN PORTION OF THE
SYTEM.

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: 12W IS FORECAST TO CONTINUE TRACKING GENERALLY
NORTHWESTWARD ALONG THE WESTERN PERIPHERY OF A STR POSITIONED TO
THE EAST THROUGH TAU 24, GRAZING THE COAST OF LUZON. AFTER TAU 24,
A STR POSITIONED OVER EASTERN CHINA IS FORECAST TO TAKE OVER AS THE
PRIMARY STEERING MECHANISM AND TURN THE SYSTEM SHARPLY WESTWARD.
THAT STR IS EXPECTED TO DRIVE 12W WESTWARD THROUGH TAU 96. AFTER
TAU 96, 12W IS FORECAST TO BEGIN TRACKING WEST-NORTHWEST AS IT
STARTS TO ROUND THE STR. REGARDING INTENSITY, 12W IS FORECAST TO
CONTINUE INTENSIFYING TO AROUND 45 KTS AT TAU 12 AS IT REMAINS IN
VERY WARM WATERS AND OFFSHORE OF THE PHILIPPINES.  QUICKLY AFTER
TAU 12, 12W IS ANTICIPATED TO MAKE LANDFALL ALONG THE WESTERN COAST
OF LUZON AND CONTINUE TO GRAZE THE COAST THROUGH TAU 24. THIS
TERRAIN INTERACTION WILL HINDER FURTHER INTENSIFICATION AND CAUSE A
STAGNANT INTENSITY. NEAR TAU 48, THE SYSTEM WILL HAVE TRAVELED A
SUFFICIENT DISTANCE FROM LUZON TO BEGIN STRENGTHENING AGAIN. A NEAR
RAPID INTENSIFICATION RATE IS FORECAST FROM TAUS 48-96 (55KTS TO
100 KTS) IN RESPONSE TO THE HIGHLY CONDUCIVE ENVIRONMEMNT (VERY HIGH
OHC AND SST WITH LOW SHEAR). AFTER TAU 96, OHC VALUES ARE EXPECTED
TO DROP AND CAUSE A MILDER INTENSIFICATION OF 10 KTS OVER 24 HOURS
TO 110 KTS AT TAU 120.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN POOR AGREEMENT
AFTER TAU 48 WITH A LARGE SPREAD IN TRACKS AFTER THE SYSTEM TRACKS
NORTH OF LUZON. THE GFS ENSEMBLE MEAN AND NAVGEM BOTH TRACK THE
VORTEX ALMOST DIRECTLY STRAIGHT NORTHWARD TOWARDS TAIWAN. IN
PARTICULAR, THE INDIVIDUAL MEMBERS OF THE GFS ENSEMBLE SPAN A VERY
LARGE AREA, RANGIN FROM WESTWARD TO NORTHWARD TO EVEN EASTWARD
TRACKS. THE ECMWF ENSEMBLE CONVERSELY IS IN MUCH BETTER AGREEMENT
ON THE WESTWARD TRACK AFTER TAU 48 WITH A MUCH SMALLER SPREAD
BETWEEN MEMBERS. THE JTWC TRACK IS PLACED CLOSER IN LINE WITH ECMWF
AND ITS ENSEMBLE WITH LOW CONFIDENCE. INTENSITY GUIDANCE IS IN
SLIGHTLY BETTER AGREEMENT, ESPECIALLY IN THE NEAR TERM. THE JTWC
INTENSITY FORECAST IS PLACED CLOSE TO CONSENSUS THROUGH TAU 36.
AFTER TAU 48, THE SPREAD IN GUIDANCE BECOMES LARGE. HAFS-A IS A
MAJOR OUTLIER DEPICTING A STAGNANT INTENSITY ALL THE WAY THROUGH
THE FORECAST PERIOD. THE REMAINDER OF GUIDANCE SUGGESTS
INTENSIFICATION THROUGH TAU 120 WITH INTENSITIES RANGING FROM 70 TO
120 KTS. THE JTWC INTENSITY FORECAST IS PLACED HIGHER THAN
CONSENSUS AFTER TAU 48 AS THE ENVIORONMENT WILL BE PRIME FOR
STRENGTHENING. 

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