WDPN31 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (YAGI) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.2N 122.6E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 100 NM EAST-NORTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 12W (YAGI) WITH CONVECTION BEGINNING TO BE BLOWN OFF TO THE
SOUTHWEST AS INCREASED NORTHEASTERLY SHEAR ACTS ON THE SYSTEM. DUE
TO THE INCREASED SHEAR, THE NORTHERN SEMICIRCLE OF THE WELL-DEFINED
LOW-LEVEL CIRCULATION CENTER HAS BECOME EXPOSED. ENVIRONMENTAL
ANALYSIS INDICATES THAT 12W IS CURRENTLY IN A MARGINALLY FAVORABLE
ENVIRONMENT FOR DEVELOPMENT CHARACTERIZED BY STRONG EQUATORWARD
OUTFLOW ALOFT AND VERY WARM SEA SURFACE TEMPERATURES OFFSET BY THE
INCREASED NORTHEASTERLY VERTICAL WIND SHEAR AND TERRAIN INTERACTION
WITH THE PHILIPPINES. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC SEEN IN THE ANIMATED
MSI. THE INITIAL INTENSITY OF 40 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE OBJECTIVE AND SUBJECTIVE INTENSITY
ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

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
   RCTP: T2.0 - 30 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 41 KTS AT 020000Z
   CIMSS AIDT: 37 KTS AT020000Z
   CIMSS DPRINT: 44 KTS AT 020000Z
   CIMSS DMINT: 38 KTS AT 012021Z
   

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: TERRAIN INTERACTION ON THE WESTERN PORTION OF THE
SYSTEM.

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: 12W IS FORECAST TO CONTINUE TRACKING GENERALLY
NORTH-NORTHWESTWARD ALONG THE WESTERN PERIPHERY OF THE DEEP-LAYERED
STR TO THE EAST THROUGH TAU 24. AFTER TAU 24, A STR POSITIONED OVER
EASTERN CHINA WILL TAKE OVER AS THE PRIMARY STEERING MECHANISM AND
BEGIN FORCING THE SYSTEM WESTWARD. 12W IS EXPECTED TO TRACK ALONG
THE SOUTHERN PERIPHERY OF THAT STR THROUGH TAU 72. AFTER TAU 72,
THE SYSTEM WILL START TO TRACK MORE WEST-NORTHWESTWARD AS IT BEGINS
TO ROUND THE STR. 12W IS FORECAST TO CONTINUE TRACKING
WEST-NORTHWESTWARD THROUGH TAU 120 AS IT TRACKS TOWARD THE LEIZHOU
PENINSULA. REGARDING INTENSITY, AS 12W MAKES LANDFALL ALONG THE
WESTERN COAST OF LUZON IN THE NEXT 6 HOURS OR SO, TERRAIN
INTERACTION WILL KEEP IT FROM FURTHER INTENSIFYING. THIS WILL CAUSE
A STAGNANT INTENSITY THROUGH TAU 24. NEAR TAU 36, 12W IS EXPECTED
TO HAVE TRAVELED A SUFFICIENT DISTANCE FROM LUZON TO BEGIN
INTENSIFYING. 12W IS FORECAST TO QUICKLY INCREASE FROM 65 KTS AT
TAU 48 TO 110 KTS AT TAU 96. THE ENVIRONMENT DURING THAT TIME
PERIOD WILL BE PRIME FOR DEVELOPMENT WITH LOW VERTICAL WIND SHEAR,
VERY WARM SEA SURFACE TEMPERATURES (30-31 C), AND STRONG
EQUATORWARD OUTFLOW ENHANCED BY THE TEJ. AS THE SYSTEM NEARS
HAINAN, THE INTENSITY IS EXPECTED TO BEGIN DECREASING AS LAND
INTERACTION STARTS TO AFFECT IT.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE HAS BEEN IMPROVING OVER
THE PAST FEW MODEL RUNS. THE GFS ENSEMBLE MEAN REMAINS AN OUTLIER
WITH A LARGE SPREAD IN MEMBERS, BUT IS STARTING TO CLOSE IN ON THE
WESTWARD TRACK. THE ECMWF ENSEMBLE NOW HAS NEARLY ALL MEMBERS
DEPICTING THE WESTWARD TURN. A MAJORITY OF THE JTWC TRACK GUIDANCE
IS NOW CONVERGING AND AS A RESULT, THE CONFIDENCE IN THE JTWC TRACK
HAS IMPROVED. INTENSITY GUIDANCE, HOWEVER, REMAINS IN POOR
AGREEMENT, ESPECIALLY AFTER TAU 36. THE MODELS AGREE ON A STAGNANT
INTENSITY THROUGH TAU 24 BUT BEGIN TO DIVERGE WITH A WIDE RANGE IN
PEAK INTENSITIES. THE JTWC INTENSITY FORECAST IS PLACED ON THE HIGH
END OF GUIDANCE DUE TO THE VERY CONDUCIVE ENVIRONMENT AFTER TAU 48.


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