WDPN31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 14W (KOINU) WARNING NR 022//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.9N 121.2E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 193 NM SOUTH OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: WESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 44 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
OVER THE PAST 12 HOURS OR SO, TYPHOON (TY) 14W (KOINU) UNDERWENT A
PERIOD OF RAPID INTENSIFICATION AS IT PASSED OVER A POOL OF HIGH
OCEAN HEAT CONTENT (OHC) OFF THE EAST COAST OF TAIWAN. WHILE
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOW THAT THE
EYE HAS FILLED OVER THE LAST SIX HOURS, TAIWAN RADAR DATA AND A
041656Z GMI 37GHZ MICROWAVE IMAGE REVEALED A 20NM WIDE LOW-LEVEL
EYE, WIDENING TO ABOUT 32NM IN THE UPPER-LEVELS. THE MICROWAVE AND
RADAR DATA ALSO INDICATE A VERY WEAK EYEWALL ON THE NORTHERN SIDE,
BEING ERODED BY MODERATE DEEP-LAYER NORTHEASTERLY SHEAR, WHILE THE
SOUTHERN EYEWALL CONTINUES TO BE VERY ROBUST. THE INITIAL POSITION
IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE DATA ABOVE.
SUBSEQUENT RADAR DATA THROUGH 042000Z SHOWS THE SYSTEM SLOWING DOWN
CONSIDERABLY, IN FACT IT MAY HAVE BECOME QUASI-STATIONARY, AS THE
OUTER BANDS BEGIN TO INTERACT WITH THE COMPLEX TERRAIN OF THE
CENTRAL MOUNTAIN RANGE (CMR). WHILE THE EYE HAS FILLED IN OVER THE
PAST FEW HOURS, THE WIND FIELD WILL STILL BE HOLDING STRONG AND
THUS THE INITIAL INTENSITY REMAINS SET AT 120 KNOTS. CONFIDENCE IN
THE INTENSITY ASSESSMENT IS HIGH BASED ON T6.0 DVORAK INTENSITY
ESTIMATES FROM PGTW, KNES AND RJTD, WITH ADDITIONAL SUPPORT FROM
THE ADT, DPRINT AND DMINT ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: OVERALL, THE SYSTEM IS BEING STEERED
WEST ALONG THE SOUTHERN SIDE OF A WEAK SUBTROPICAL RIDGE (STR)
SITUATED TO THE NORTH, ANCHORED OVER SOUTHERN CHINA AND EAST OF
OKINAWA. HOWEVER, LOCALIZED TERRAIN EFFECTS WILL DOMINATE THE TRACK
MOTION IN THE NEAR-TERM. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   KNES: T6.0 - 115 KTS
   CIMSS ADT: 122 KTS AT 041730Z
   DPRINT: 117 KTS AT 041800Z
   DMINT:  124 KTS AT 041651Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: EQUATORWARD OUTFLOW CHANNEL; TERRAIN INTERACTION

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: HAVING PASSED DIRECTLY OVER LANYU ISLAND
OVERNIGHT, TYPHOON KAINO HAS MOVED SLOWLY WEST-SOUTHWESTWARD, BUT
HAS NOW SLOWED TO A CRAWL AS IT APPROACHES THE SOUTHERN TIP OF
TAIWAN. THE DEEP-LAYER STEERING PATTERN REMAINS RELATIVELY WEAK,
WITH A WEAKNESS IN THE STR DUE NORTH OF THE SYSTEM. COMBINED WITH
THE SIGNIFICANT INFLUENCES OF THE TERRAIN ON LANDFALLING TROPICAL
CYCLONES ON THE EAST COAST OF TAIWAN, THE NEAR-TERM TRACK MOTION IS
HIGHLY UNCERTAIN. THE FORECAST CALLS FOR THE SYSTEM TO TRACK VERY
SLOWLY OVER THE SOUTHERN TIP OF TAIWAN, THEN TURN NORTHWESTWARD UP
THE COAST TO THE WEST OF KAOHSIUNG OVER THE NEXT 12 TO 18 HOURS.
THEREAFTER, THE RIDGE TO THE NORTH SHOULD STRENGTHEN A NOTCH, BUT
IS EXPECTED TO REMAIN RELATIVELY WEAK, WHICH MEANS TY 14W WILL ONLY
SLOWLY MOVE AWAY FROM TAIWAN THROUGH TAU 48. DEEP-LAYER SHEAR IS
RELATIVELY HIGH BUT IS FORECAST TO SLACKEN OVER THE NEXT DAY OR
TWO. HOWEVER, MID-LEVEL SHEAR IS BOOMING AND NOT FORECAST TO WEAKEN
MUCH THROUGH THE SAME TIME PERIOD. THE ENHANCED MID-LEVEL SHEAR
COMBINED WITH THE LOW-LEVEL INFLOW AND CORE DISRUPTION DUE TO
DOWNSLOPE WINDS OFF THE CMR, WILL SERVE TO RAPIDLY WEAKEN THE
SYSTEM AS IT MOVES INTO THE TAIWAN STRAIT, THOUGH THE SYSTEM IS
FORECAST TO REMAIN A TYPHOON THROUGH TAU 48. AFTER THIS POINT,
INGESTION OF LOW THETA-E AIR STREAMING DOWN THE TAIWAN STRAIT
BEHIND A COLD FRONT WILL SERVE TO RAPIDLY WEAKEN THE SYSTEM AND
LEAD TO ITS ULTIMATE DEMISE. AFTER TAU 48, THE SYSTEM WILL TURN
SHARPLY SOUTHWESTWARD ALONG THE SOUTHERN SIDE OF THE LOW- TO
MID-LEVEL RIDGE OVER CENTRAL CHINA AND IS CURRENTLY EXPECTED TO
REMAIN OFFSHORE AS IT WEAKENS AND ULTIMATELY DISSIPATES SOUTH OF
HONG KONG. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
RELATIVELY GOOD AGREEMENT THROUGH TAU 72, WITH THE CONSENSUS
MEMBERS CONSTRAINED TO A 100NM ENVELOPE WITH NAVGEM ON THE NORTH
AND GFS ON THE SOUTH. OF NOTE, ONLY THE HWRF AND COAMPS-TC
MESOSCALE MODELS ARE PICKING UP ON A SLIGHT NORTHWEST TRACK UP THE
WEST SIDE OF TAIWAN. THUS THE JTWC FORECAST TRACK DEVIATES ABOUT
30NM FROM THE PACK THROUGH TAU 12, THOUGH THE FORECAST TRACK
CLOSELY ALIGNS WITH THE CONSENSUS MEAN AFTER TAU 24. CONFIDENCE TO
TAU 72 IS MEDIUM, PRIMARILY DUE TO THE HIGH LIKELIHOOD OF AN ERRATIC
TRACK IN THE NEAR-TERM AS THE SYSTEM CROSSES TAIWAN. IN THE LATER
TAUS, THE BULK OF THE GUIDANCE EXCEPT FOR NAVGEM, JGSM AND THE
UKMET ENSEMBLE MEAN, TURN THE SYSTEM SHARPLY SOUTHWESTWARD.
SIGNIFICANT ALONG-TRACK SPREAD EMERGES AFTER TAU 72, WITH THE GFS
AND GFS ENSEMBLE MEAN RACING OUT FORWARD OF THE ECMWF AND THE OTHER
CONSENSUS MEMBERS. OF NOTE, THE UKMET ENSEMBLE MEAN TURNS THE
SYSTEM NORTH, PASSES THROUGH THE TAIWAN STRAIT AND ENDS UP WEST OF
OKINAWA BY TAU 120, WHILE THE NAVGEM AND JGSM DISSIPATE THE SYSTEM
ALONG THE EAST COAST OF CHINA. THE UKMET ENSEMBLE SOLUTION IS
HIGHLY UNLIKELY AND IS DISCARDED, BUT IF THE WEAKNESS IN THE RIDGE
TO THE NORTH PERSISTS, THE OTHER TWO OUTLIER SOLUTIONS ARE NOT
COMPLETELY UNREALISTIC. THE JTWC FORECAST IS PLACED CLOSE TO THE
ECMWF SOLUTION AFTER TAU 72, WITH LOW CONFIDENCE. INTENSITY
GUIDANCE IS IN CLOSE AGREEMENT ON A STEADY WEAKENING TREND THROUGH
THE FORECAST PERIOD AND THE JTWC FORECAST LIES CLOSE TO THE
CONSENSUS MEAN WITH MEDIUM CONFIDENCE. 

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