WDPN32 PGTW 242100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 05W (GAEMI) WARNING NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.7N 121.4E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 25 NM SOUTH-SOUTHWEST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 33 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON (TY) 05W (GAEMI) MADE LANDFALL ALONG THE NORTHEASTERN COAST
OF TAIWAN AT APPROXIMATELY 241600Z, AFTER COMPLETING A RATHER WILD
COUNTER-CLOCKWISE LOOP ALONG THE EAST COAST OF TAIWAN DURING THE
PRECEDING 12 HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY AS WELL AS ANIMATED RADAR DATA FROM THE CENTRAL WEATHER
ADMINISTRATION (CWA) SHOWS THAT THE RADAR EYE FEATURE RAPIDLY
DISINTEGRATED AS IT APPROACHED THE COAST, AND COMPLETELY
DISAPPEARED AS OF THE 1800Z HOUR. THE EIR SUGGESTS A SIGNIFICANT
AMOUNT OF NORTHERLY WIND SHEAR, WITH CONVECTION RAPIDLY ERODING
ACROSS THE NORTHERN HEMISPHERE OF THE CIRCULATION. A 241730Z
NOAA-20 ATMS 88.2GHZ MICROWAVE IMAGE SHOWS A VERY SMALL INNER CORE
OF CONVECTION OVER NORTH-CENTRAL TAIWAN, WITH A CLEAR MOAT OF DRY
AIR DRAPED ACROSS THE NORTHERN HEMISPHERE AND STRONG CONVECTIVE
BANDING FLOWING FROM THE WEST OVER THE SOUTHERN HALF OF TAIWAN. THE
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON RADAR
FIX DATA. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE,
BASED PRIMARILY UPON THE RJTD AND RCTP OVER LAND DVORAK FIX
ESTIMATES BETWEEN T5.0 AND T5.5, THE MOST RECENT SATCON AND A DMINT
ESTIMATE FROM 241729Z OF 88 KNOTS. NOW THAT THE SYSTEM IS OVER THE
RUGGED TERRAIN OF CENTRAL TAIWAN, THE LOW-LEVEL VORTEX IS LIKELY
SEPARATING FROM THE UPPER-LEVEL VORTEX. THIS, COMBINED WITH RAPIDLY
INCREASING AND VERY UNFAVORABLE SHEAR, CURRENTLY ESTIMATED BY CIMSS
AT 23 KNOTS, IS LEADING TO RAPID WEAKENING OF THE SYSTEM. 
UPPER-LEVEL OUTFLOW REMAINS RADIAL AND WARM WATERS AWAIT THE SYSTEM
ON THE OTHER SIDE OF TAIWAN.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T5.0 - 90 KTS
   RCTP: T5.5 - 102 KTS
   CIMSS SATCON: 101 KTS AT 241500Z
   CIMSS DMINT: 88 KTS AT 241729Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 20-25 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

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

FORECAST DISCUSSION: AFTER MAKING ITS COUNTER-CLOCKWISE LOOP EAST
OF TAIWAN, TY GAEMI FINALLY DECIDED TO COME ASHORE AROUND 1600Z AND
HAS NOW PICKED UP SPEED, HEADING TO THE WEST-NORTHWEST, PASSING
JUST SOUTH OF TAOYUAN AS OF THIS WRITING. THE VORTEX HAS LIKELY
DECOUPLED, WITH THE MID- AND UPPER-LEVEL VORTEX RACING
WEST-NORTHWESTWARD, WHILE THE LOW-LEVEL VORTEX IS MOST LIKELY BEING
LEFT BEHIND, DECAYING OVER THE RUGGED TERRAIN. A LEE-SIDE JUMP
SCENARIO IS FAVORED IN THIS SETUP, AND THE HIGH-RESOLUTION MODEL
GUIDANCE SUGGESTS THE LOW-LEVEL VORTEX WILL REFORM ON THE WESTERN
COAST OF TAIWAN AS THE UPPER-LEVEL VORTICITY BUILDS BACK DOWN TO
THE SURFACE. THEREAFTER, A BRIEF PERIOD OF ERRATIC TRACK MOTION IS
POSSIBLE, WITH THE POTENTIAL FOR ANOTHER LOOP, BEFORE THE SYSTEM
REFORMS ENOUGH TO RESUME ITS WEST-NORTHWESTWARD TRACK. THE TRACK
MADE GOOD IN THE FORECAST CALLS FOR THE SYSTEM TO TRACK ALONG THE
SOUTHWEST SIDE OF THE STR TO THE EAST, GENERALLY TOWARDS A
DEVELOPING WEAKNESS IN THE RIDGE AND WILL APPROACH THE EASTERN
COAST OF CHINA WITHIN THE NEXT 12 TO 18 HOURS. AFTER LANDFALL, THE
SYSTEM IS FORECAST TO CONTINUE TRACKING NORTHWESTWARD THROUGH THE
REMAINDER OF THE FORECAST PERIOD. WHILE THE UPPER-LEVEL PATTERN IS
GENERALLY FAVORABLE FOR THE NEXT 12 TO 24 HOURS, AND SSTS IN THE
STRAIT ARE WARM, THE SHREDDING OF THE DEEP, ALIGNED VORTEX AND
CONTINUED MODERATE TO HIGH NORTHERLY SHEAR, WILL PRECLUDE ANY
REINTENSIFICATION AS THE SYSTEM CROSSES THE TAIWAN STRAIT. THE
FORECAST CALLS FOR LANDFALL ALONG THE CHINESE COAST AS A MINIMAL
TYPHOON, FOLLOWED BY RAPID WEAKENING OVER CHINA, WITH FULL
DISSIPATION BY TAU 48. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN TIGHT
AGREEMENT, WITH MINIMAL MODEL SPREAD THROUGH THE FORECAST PERIOD.
THE ONE OUTLIER IS THE NAVGEM, WHICH TRACKS THE SYSTEM ALMOST DUE
WEST THROUGH TAU 12, BEFORE REJOINING THE PACK. IN LIGHT OF THE
POTENTIAL ERRATIC TRACK MOTION, AND HISTORICAL TRENDS, THIS
SCENARIO IS NOT OUTSIDE OF THE REALM OF THE POSSIBLE AND SHOULD BE
CLOSELY MONITORED. HOWEVER, THE JTWC FORECAST TAKES A MORE
WEST-NORTHWEST TRACK, ALONG THE SOUTHERN EDGE OF THE GUIDANCE
PACKAGE, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD
AGREEMENT THAT THE SYSTEM WILL RAPIDLY WEAKEN THROUGH THE FORECAST
PERIOD AND DISSIPATE BY TAU 48. 

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