WDPN32 PGTW 310900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 02W (TWO) WARNING 
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.5N 111.9E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 168 NM SOUTHWEST OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAGGED,
ELONGATED AND DISORGANIZED LOW LEVEL CIRCULATION (LLC), WITH
MULTIPLE EMBEDDED MESOVORTICES. THE PRIMARY VORTEX BEING TRACKED
OVER THE PAST SIX HOURS HAS TRACKED RAPIDLY NORTHWESTWARD AND
CURRENTLY LIES JUST EAST OF ZHANJIANG, CHINA. HOWEVER, ANIMATED
HIGH-RESOLUTION MSI, ANIMATED RADAR DATA AS WELL AS A 310548Z AMSR2
37GHZ MICROWAVE IMAGE SUGGESTS THE POSSIBILITY OF A SECOND
CIRCULATION CENTER NEAR 20N 112.5E, MOVING MORE SLOWLY NORTHWARD.
THIS SUGGESTS THE VORTEX BEING TRACKED EARLIER WAS IN FACT JUST A
SECONDARY MESOVORTEX AND NOT THE ACTUAL LLCC OF THE TROPICAL STORM.
THE INITIAL POSITION IS THUS ASSESSED WITH LOW CONFIDENCE, ROUGHLY
IN THE CENTROID POSITION BETWEEN THE TWO VORTICES, AND ROUGHLY AT
THE MIDPOINT BETWEEN THE PGTW, KNES AND RJTD FIX POSITIONS. THE
INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, HEDGED
SLIGHTLY HIGHER THAN THE BULK OF THE AGENCY DVORAK CURRENT
INTENSITY ESTIMATES IN LIGHT OF AN EARLIER ASCAT PASS WHICH SHOWED
30 KNOT WINDS THROUGHOUT THE SOUTHEASTERN SECTOR OF THE CIRCULATION.
THE ENVIRONMENT IS MARGINAL AT BEST, WITH SSTS COOLING AS THE
SYSTEM TRACKS NORTHWARD, AND MODERATE NORTHEASTERLY VWS OFFSETTING
THE STRONG EQUATORWARD OUTFLOW. THE SYSTEM IS TRACKING
NORTHWESTWARD ALONG THE WESTERN SIDE OF A DEEP-LAYER SUBTROPICAL
RIDGE (STR) TO THE EAST.

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

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER STR
CENTERED TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 02W (TWO) IS FORECAST
TO GENERALLY TRACK NORTHWARD TOWARDS THE CHINESE COAST OVER THE
NEXT 12 HOURS. TRACK DEVIATIONS TO THE EAST OR WEST ARE LIKELY AS
THE TWO VORTICES DESCRIBED ABOVE ROTATE ABOUT A CENTROID WHILE
OVERALL TRACKING NORTHWARD. LANDFALL IN THE VICINITY OF YANGJIANG,
CHINA IS ANTICIPATED WITHIN THE NEXT 12 HOURS. ONCE THE SYSTEM
MOVES ASHORE IT WILL BEGIN TRACKING MORE NORTHEASTWARD AS THE STR
TO THE EAST BUILDS AND EXTENDS SOUTHWESTWARD OVER THE PHILIPPINES.
BY THE END OF THE FORECAST PERIOD, THE REMNANTS OF TD 02W WILL
BEGIN TO INTERACT AND MERGE WITH THE TAIL END OF THE MEIYU BOUNDARY
AND TURN MORE SHARPLY EASTWARD. DUE TO THE MODERATE NORTHEASTERLY
SHEAR, PARTICULARLY PRONOUNCED IN THE MID-LEVELS, NO SIGNIFICANT
INTENSIFICATION IS EXPECTED BEFORE TD 02W MAKES LANDFALL. HOWEVER,
THE BUILDING STR NOSING INTO THE SOUTH CHINA SEA COULD LEAD TO A
STRENGTHENING GRADIENT ON THE SOUTHEAST SIDE OF THE STORM AND
GENERATE SOME GALE-FORCE WINDS IN THAT SECTOR AS THE SYSTEM SLIDES
NORTHWARD TOWARDS THE COAST. WINDS ON IN THE REMAINDER OF THE
CIRCULATION WILL REMAIN WELL BELOW GALE-FORCE. ONCE ASHORE,
FRICTIONAL EFFECTS AND INCREASING SHEAR WILL TEAR THE SYSTEM APART,
LEADING TO FULL DISSIPATION NO LATER THAN TAU 36 AND LIKELY BY TAU
24. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT
THAT THE SYSTEM WILL THE SYSTEM WILL TRACK NORTHWARD, AND MAKE
LANDFALL WITHIN THE NEXT 12 HOURS BETWEEN YANGJIANG AND SHANGCHUAN
DAO, CHINA. ALL AVAILABLE GUIDANCE CONCURS THAT AFTER LANDFALL THE
SYSTEM WILL TRACK NORTHEASTWARD ROUGHLY PARALLEL TO THE CHINESE
COAST THEN TURN SHARPLY EASTWARD AFTER TAU 36. INTENSITY GUIDANCE,
WITH THE EXCEPTION OF HWRF, SUPPORTS A FLAT INTENSITY TREND THROUGH
LANDFALL FOLLOWED BY RAPID WEAKENING OVER LAND. THE HWRF SPIKES THE
SYSTEM UP TO 40 KNOTS PRIOR TO LANDFALL, BUT THIS APPEARS UNLIKELY
DUE TO THE MODERATE SHEAR, SHORT TIME OVER WATER AND THE PRESENCE
OF MULTIPLE VORTICES IN A STRONGLY TILTED ENVIRONMENT. THE JTWC
TRACK FORECAST IS ASSESSED AS MEDIUM CONFIDENCE DUE TO UNCERTAINTY
IN THE INITIAL POSITION, WHILE THE INTENSITY FORECAST IS ASSESSED
AS HIGH CONFIDENCE. 

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