WDPN31 PGTW 080300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (LIONROCK) WARNING 
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.8N 110.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 180 NM NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A PARTIALLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC), WITH CURVED BANDS OF
DEEP CONVECTION WELL ENTRENCHED TO THE SOUTH AND EAST OF THE LLCC,
WITH WEAKER CONVECTIVE BANDS STARTING TO DEVELOP ON THE WESTERN
SIDE WITHIN THE PAST COUPLE OF HOURS. THE RADIUS OF MAXIMUM WINDS
CONTINUES TO SLOWLY CONSOLIDATE THOUGH A BAND OF HIGHER, NEAR-GALE
FORCE WINDS, REMAINS IN PLACE IN A WIDE ARC APPROXIMATELY 125NM OUT
FROM THE CENTER EXTENDING FROM SOUTH OF HONG KONG TO WEST OF THE
PHILIPPINES. THE INITIAL POSITION IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON SPIRAL BAND ANALYSIS OF THE EXPOSED LLCC AND
ANIMATED RADAR DATA. THE INITIAL INTENSITY OF 35 KNOTS IS ASSESSED
WITH MEDIUM CONFIDENCE, SLIGHTLY HIGHER THAN THE MAJORITY OF THE
AGENCY DVORAK CURRENT INTENSITY ESTIMATES IN LIGHT OF THE ADT AND
SATCON ESTIMATES AND OVERALL IMPROVING CONVECTIVE SIGNATURE.  THE
SYSTEM REMAINS IN A RELATIVELY FAVORABLE ENVIRONMENT CHARACTERIZED
BY WARM (29-30C) SSTS, LOW (5-10 KTS) VWS AND STRONG POLEWARD AND
EQUATORWARD OUTFLOW. TS 22W IS CURRENTLY MOVING NORTHWARD ALONG THE
SOUTHWESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE NORTHEAST.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK. 

CURRENT STEERING MECHANISM: SOUTHWEST PERIPHERY OF A DEEP-LAYER STR
CENTERED FAR TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 35 KTS AT 071751Z
   CIMSS ADT: 34 KTS AT 072340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: PROXIMITY TO LAND. 

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: TS 22W IS CURRENTLY MOVING NORTHWARD ALONG THE
SOUTHWEST SIDE OF A MASSIVE STR COMPLEX CENTERED SOUTHEAST OF
JAPAN. THE TRACK IS EXPECTED TO CONTINUE NORTHWARD THROUGH TAU 24
AS THE RIDGE REMAINS FIRMLY ENTRENCHED TO ITS NORTHEAST. THE SYSTEM
IS EXPECTED TO MAKE LANDFALL ALONG THE COAST OF HAINAN ISLAND
WITHIN THE NEXT 12 HOURS, THEN CROSS THE ISLAND, EMERGING INTO THE
GULF OF TONKIN NEAR TAU 36. BY TAU 36 A NEW RIDGE CENTER BEGINS TO
DEVELOP OVER SOUTH-CENTRAL CHINA, DUE NORTH OF TS 22W, WHICH WILL
BLOCK ANY FURTHER POLEWARD MOVEMENT AND TURN THE SYSTEM TO THE
WEST. BY TAU 48 THE RIDGE REORIENTS TO A SOUTHWEST-NORTHEAST AXIS,
PUSHING TS 22W ONTO A SOUTHWESTWARD TRACK THROUGH THE REMAINDER OF
THE FORECAST PERIOD. A SECOND LANDFALL IS EXPECTED IN NORTH CENTRAL
VIETNAM AROUND TAU 72. WHILE THE PROXIMITY TO LAND AND THE BROAD
NATURE OF THE SYSTEM WILL SERVE AS A BRAKE ON DEVELOPMENT, THE
OVERALL FAVORABLE ENVIRONMENT WILL SUPPORT INTENSIFICATION TO 40
KNOTS PRIOR TO LANDFALL, FOLLOWED BY SLOW WEAKENING AS THE SYSTEM
CROSSES HAINAN. DUE TO THE BROAD NATURE OF THE CIRCULATION, EVEN
WHEN CROSSING HAINAN, GALE FORCE WINDS ARE EXPECTED IN THE OFFSHORE
AREAS OF THE ISLAND, PARTICULARLY TO THE NORTH. THE SYSTEM IS
EXPECTED TO REEMERGE INTO THE GULF OF TONKIN AS A WEAK TROPICAL
STORM, BUT INCREASED EASTERLY SHEAR WEAK CONVERGENT FLOW ALOFT WILL
INHIBIT MUCH IN THE WAY OF INTENSIFICATION, WITH A SECOND PEAK OF
40 KNOTS EXPECTED PRIOR TO LANDFALL IN VIETNAM. ONCE ASHORE IN
VIETNAM THE SYSTEM WILL RAPIDLY DISSIPATE OVER THE MOUNTAINOUS
TERRAIN. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN OVERALL GOOD AGREEMENT
THROUGH TAU 72, WITH THE GFS AND HWRF BEING THE ONLY CONTRARIAN
MEMBERS, SHOWING A SHARP TURN SOUTHWARD AFTER TAU 36. THE REMAINDER
OF THE GUIDANCE MEMBERS ARE PACKED WITHIN A 115NM ENVELOPE AT TAU
72, INCREASING AFTER LANDFALL AS THE VORTEX DISSIPATES. THE JTWC
FORECAST LIES ON LEFT SIDE OF THE ENVELOPE FOR THE DURATION OF THE
FORECAST WITH MEDIUM CONFIDENCE. THE INTENSITY GUIDANCE MEMBERS ALL
CONCUR ON THE OVERALL TRENDS, THOUGH THE COAMPS-TC MEMBERS CARRY ON
THE INTENSIFICATION TREND WHILE OVER HAINAN, WHICH SEEMS UNLIKELY.
THUS THE JTWC FORECAST LIES WITHIN THE GUIDANCE ENVELOPE BUT TAKES
INTO ACCOUNT TERRAIN INFLUENCES TO LIE AT THE LOWER END OF THE
GUIDANCE PACKAGE THROUGH TAU 48, THEN CLOSELY TRACKS THE HWRF
SOLUTION THEREAFTER WITH MEDIUM CONFIDENCE. 

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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