WDPN31 PGTW 050300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 14W (KOINU) WARNING NR 023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.0N 120.8E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 190 NM SOUTH-SOUTHWEST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 37 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI), ANIMATED TAIWAN
WEATHER AGENCY RADAR DATA AND SURFACE OBSERVATIONS FROM HENGCHUN,
INDICATE THAT TYPHOON (TY) 14W (KOINU) MADE LANDFALL ALONG THE FAR
SOUTHEASTERN TIP OF TAIWAN AT OR SLIGHTLY BEFORE 050000Z. THE 0000Z
SURFACE OBSERVATION FROM HENGCHUN SHOWED NORTH WINDS AT 68 KNOTS,
INDICATING THE CENTER WAS STILL EAST OF THE STATION. WINDS WERE
RELATIVELY LIGHT GIVEN THAT THE STATION WAS IN THE WESTERN EYEWALL
PER THE RADAR DATA, THOUGH THAT SIDE OF THE EYEWALL WAS
SIGNIFICANTLY WEAKER THAN THE SOUTHERN PORTION WHICH HAS REMAINED
OVER WATER. THE INITIAL POSITION WAS ASSESSED WITH HIGH CONFIDENCE
BASED ON THE RADAR DATA. THE INITIAL INTENSITY IS ASSESSED WITH
MEDIUM CONFIDENCE, SET AT A GENEROUS 110 KNOTS, BASED ON THE
PREPONDERANCE OF THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES.
HOWEVER, THE HIGHEST OF THE WINDS ARE OVER WATER, IN THE SOUTHERN
EYEWALL AND ARE UNLIKELY TO BE CAPTURED IN THE SURFACE WIND
OBSERVATIONS. BROADLY SPEAKING THE SYSTEM IS TRACKING WESTWARD
UNDER THE INFLUENCE OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) DRAPED
ACROSS EAST CHINA SEA, BUT A WEAKNESS IN THE RIDGE SITUATED TO THE
NORTH MEANS THAT IN THE CONGREGATE, THE STEERING ENVIRONMENT IS
WEAK AT BEST, SUCH THAT LOCALIZED TERRAIN-INDUCED EFFECTS WILL HAVE
AN OUTSIZED IMPACT ON THE TRACK MOTION FOR THE NEXT 12 TO 24 HOURS.
ENVIRONMENTAL ANALYSIS REVEALS A MARGINAL ENVIRONMENT, WITH WARM
SSTS AND MODERATE EQUATORWARD OUTFLOW OFFSET BY MODERATE
NORTHEASTERLY SHEAR, FRICTIONAL EFFECTS AND DRY DOWNSLOPE WINDS
ENTRAINING INTO THE CORE OF THE SYSTEM. THE LATEST WATER VAPOR
IMAGERY SHOWS THE STEADY REDUCTION IN OUTFLOW ALOFT WHICH IS
COMPOUNDING THE ALREADY MARGINAL ENVIRONMENT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN SIDE OF A DEEP-LAYER
SUBTROPICAL RIDGE TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T5.0 - 90 KTS
   CIMSS SATCON: 105 KTS AT 042030Z
   CIMSS ADT: 119 KTS AT 042330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: FRICTIONAL EFFECTS AND DRY AIR ENTRAINMENT. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: AFTER MAKING LANDFALL, TY 14W HAS QUICKLY
CROSSED THE NARROWEST PORTION OF THE ISLAND AND IS ALREADY MOVING
BACK OVER THE SOUTHERN PORTION OF THE TAIWAN STRAIT BY THE 0100Z
HOUR. SINCE THE OVERALL STEERING PATTERN IS RELATIVELY WEAK, TRACK
MOTION OVER THE NEXT 12 TO 24 HOURS IS LIKELY TO BE SOMEWHAT
ERRATIC, WITH A MORE NORTHWEST TRACK UP THE WEST COAST OF TAIWAN
PARTICULARLY LIKELY AND IN FACT, THE LATEST RADAR IMAGERY SUGGESTS
WE MAY BE SEEING THE EARLY INDICATIONS OF THIS HAPPENING. BY ABOUT
TAU 24 HOWEVER, THE RIDGE TO THE NORTH IS EXPECTED TO STRENGTHEN A
BIT, ALLOWING TY 14W TO KICK OUT TOWARDS THE WEST, INTO THE OPEN
WATERS OF THE STRAIT. THE SYSTEM WILL SLOW DOWN BY TAU 48 AS IT
APPROACHES THE COAST OF CHINA, BEING BLOCKED BY A LOW- TO MID-LEVEL
HIGH THAT PUSHES DOWN OUT OF EAST-CENTRAL CHINA. THE SYSTEM IS
ALREADY STARTING TO RAPIDLY WEAKEN AS IT LOSES OUTFLOW IN THE
UPPER-LEVELS, WHILE THE INGESTION OF DRY DOWNSLOPE AIR INTO THE THE
SYSTEM DEGRADES THE INNER-CORE. INTENSITY WILL DROP OFF RAPIDLY
OVER THE NEXT 12 TO 18 HOURS, THEN LEVEL OFF A BIT AS THE SYSTEM
MOVES AWAY FROM TAIWAN. A FASTER RATE OF WEAKENING AFTER TAU 24 IS
POSSIBLE IF THE DRY AIR SWEEPING SOUTH DOWN THE STRAIT CAN REACH
THE CORE OF THE SYSTEM, AS SOME OF THE GLOBAL MODEL FIELDS SUGGEST.
THE MESOSCALE MODELS HOWEVER SHOW A MORE RESILIENT CORE, HOLDING
OFF THE COOL, DRY AIR INGESTION UNTIL AFTER TAU 48. THE FORECAST
FAVORS THE LATTER TREND, WITH THE ONSET OF RAPID WEAKENING AFTER
TAU 48, AS THE LOW THETA-E AIR FINALLY PUNCHES ITS WAY INTO THE
CORE OF THE SYSTEM. AS IT WEAKENS, THE SYSTEM WILL TURN SHARPLY
SOUTHWESTWARD AS IT COMES UNDER THE STEERING INFLUENCE OF
PROGRESSIVELY LOWER LEVELS OF ATMOSPHERE. THE SYSTEM WILL PASS
SOUTH OF HONG KONG AS A MINIMAL TROPICAL STORM, AND BE NEARING
DISSIPATION BY TAU 120 EAST OF HAINAN ISLAND. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU
72, WITH ALL OF THE CONSENSUS MODELS CONFINED TO A 100NM WIDE
ENVELOPE GENERALLY POINTED TOWARDS THE WEST. SOME SLIGHT DEVIATIONS
TO THE NORTH AND SOUTH ARE DISPLAYED IN THE GUIDANCE, BUT OVERALL,
CONFIDENCE IS HIGH IN THE JTWC FORECAST TRACK, WHICH IS PLACED
CLOSE TO THE CONSENSUS MEAN. AFTER TAU 72, ALL CONSENSUS MEMBERS
NOW AGREE ON A SHARP TURN TOWARDS THE SOUTHWEST, THOUGH THERE IS
STILL SIGNIFICANT ALONG-TRACK SPREAD, WITH THE GFS AND GEFS
ENSEMBLE FAR OUTPACING THE NAVGEM AND ECMWF. THE JTWC FORECAST LIES
ALONG THE CONSENSUS TRACK BUT REMAINS MUCH SLOWER, PARTICULARLY
AFTER TAU 120, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN
GOOD AGREEMENT THAT THE SYSTEM WILL STEADILY WEAKEN THROUGH THE
FORECAST PERIOD, THOUGH SOME MEMBERS (COAMPS-TC) SHOW A FASTER RATE
OF WEAKENING WHILE THE HAFS-A AND HWRF SHOW A RELATIVELY FLAT
INTENSITY THROUGH TAU 36. THE JTWC FORECAST LIES ALONG THE
CONSENSUS MEAN WITH MEDIUM CONFIDENCE. 

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