WDPN31 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 14W (KOINU) WARNING NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.8N 128.0E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 462 NM SOUTH OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 31 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS TYPHOON
(TY) 14W (KOINU) CONTINUING TO SLOWLY CONSOLIDATE, THOUGH THE EYE
THAT WAS EVIDENT EARLIER, HAD IN THE SIX HOURS UP TO 1800Z, FILLED
IN. AT THE 011800Z HOUR, EIR DEPICTED AN IRREGULAR CENTRAL DENSE
OVERCAST (CDO) WITH DEEP FLARING CONVECTION PARTICULARLY NOTABLE IN
THE SOUTHERN HEMISPHERE. SUBSEQUENT EIR INDICATES THE CONVECTIVE
HOT TOWERS ARE STARTING TO WRAP UPSHEAR ON THE EAST SIDE OF THE LOW
LEVEL VORTEX, WITH ADDITIONAL HOT TOWERS FLARING ON THE NORTHWEST
SIDE, BEGINNING TO FORM A BANDING EYE TYPE FEATURE. HOWEVER,
PREVIOUS ATTEMPTS TO WRAP THE CONVECTION UP THE EAST SIDE HAVE
FAILED, SO IT REMAINS TO BE SEEN IF THIS ROUND WILL BE SUCCESSFUL.
GFS AREA-AVERAGED SOUNDINGS INDICATE THE PRESENCE OF MODERATE
EASTERLY SHEAR BELOW THE OUTFLOW LAYER AS WELL AS RELATIVELY DRY
AIR IN THE MID- TO UPPER-LEVELS, WHICH WOULD SERVE TO HINDER
SUSTAINED CONVECTIVE DEVELOPMENT AND SUSTAINMENT ON THE EASTERN
SIDE OF THE CIRCULATION. A TIMELY 011728Z AMSR2 37GHZ IMAGE SHOWED
A VERY WELL-DEFINED LOW LEVEL MICROWAVE EYE FEATURE, WHICH
SUPPORTED THE INITIAL POSITION WITH HIGH CONFIDENCE. MEANWHILE THE
89GHZ IMAGE SHOWED A SOLID INNER EYEWALL, WITH FRAGMENTARY DEEP
CONVECTION ON THE NORTHEAST SIDE, AND WHAT COULD BE THE INITIAL
HINTS AT A SECONDARY EYEWALL ALREADY STARTING TO FORM TO THE SOUTH
OF THE CENTER. THE INITIAL INTENSITY IS SET WITH MEDIUM CONFIDENCE
BASED ON THE OVERALL AGREEMENT OF AVAILABLE SUBJECTIVE AND
OBJECTIVE INTENSITY ESTIMATES. ENVIRONMENTAL ANALYSIS REVEALS
FAVORABLE CONDITIONS, WITH LOW (10-15 KTS) EASTERLY WIND SHEAR,
ROBUST RADIAL OUTFLOW AND AN ENHANCED EQUATORWARD OUTFLOW CHANNEL,
AND ZESTY SSTS. THE SYSTEM IS CURRENTLY TRACKING TOWARDS THE
NORTHWEST ALONG THE WESTERN SIDE OF A DEEP-LAYER SUBTROPICAL RIDGE
(STR) CENTERED TO THE NORTHEAST.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR). 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.0 - 65 KTS
   KNES: T4.5 - 77 KTS
   CIMSS SATCON: 82 KTS AT 011724Z
   CIMSS ADT: 84 KTS AT 011730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: MODERATE MID-LEVEL SHEAR AND DRY AIR.

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: WHILE TY 14W HAS CONTINUED TO INTENSIFY OVER
THE PAST SIX HOURS, THE PACE OF INTENSIFICATION HAS SLOWED AS THE
SYSTEM CONTINUES TO SLOWLY CONSOLIDATE AND CONTINUES TO STRUGGLE A
BIT AGAINST MODERATE MID- TO UPPER-LEVEL SHEAR AND A BIT OF DRY AIR
IN THE MID-LEVELS. THE SYSTEM IS EXPECTED TO TRACK NORTHWESTWARD
THROUGH THE NEXT 36 HOURS ALONG THE WEST SIDE OF A DEEP STR TO THE
EAST. AROUND TAU 48, THE SYSTEM REACHES AN INFLECTION POINT WHEN
THE RIDGE BUILDS IN ROUGHLY ALONG AN OKINAWA TO FUZHOU AXIS, AND
THE TRACK SHIFTS OVER TO A MORE WESTWARD DIRECTION. BY TAU 72, THE
SYSTEM WILL BE TRACKING WESTWARD TOWARDS THE SOUTHERN COAST OF
TAIWAN, WITH LANDFALL ANTICIPATED ALONG THE FAR SOUTHERN PORTION OF
TAIWAN SHORTLY AFTER TAU 72. THE SYSTEM IS EXPECTED TO SLOW DOWN AS
IT APPROACHES TAIWAN, WITH POTENTIALLY SLOW, ERRATIC MOTION TO
FOLLOW AFTER LANDFALL. THE SYSTEM IS FORECAST TO MOVE BACK OVER
WATER TO THE WEST OF KAOHSIUNG BY TAU 96 THOUGH TRACK SPEEDS WILL
BE QUITE SLOW AS IT CONTINUES TRACKING WEST THROUGH THE REMAINDER
OF THE FORECAST PERIOD. IN TERMS OF INTENSITY, IF THE RECENT BURST
OF CONVECTIVE ACTIVITY CAN SUSTAIN ITSELF AND WRAP AROUND THE CORE
AND ESTABLISH AN EYE, INTENSITY ESTIMATES WILL RAPIDLY INCREASE.
HOWEVER, THE PRESENCE OF DRY AIR AND MID-LEVEL SUB-OUTFLOW LAYER
SHEAR IS EXPECTED TO HAVE A MAJOR ROLE IN KEEPING A LID ON THE
INTENSIFICATION RATE. IN FACT, THE GFS, HAFS-A AND HWRF ALL SHOW AN
INFLUX OF MORE DRY AIR FROM THE EAST, PARTICULARLY AFTER TAU 24,
ALONG WITH INCREASED SHEAR AFTER TAU 48. THESE ARE LIKELY TO BE
OFFSET BY THE STRONG RADIAL OUTFLOW AND THE INNER-CORE, ONCE
ESTABLISHED, IS LIKELY TO BE ABLE TO FIGHT OFF THE SHEAR AND DRY
AIR TO AN EXTENT. IN NET, THE SYSTEM IS STILL EXPECTED TO
INTENSIFY, BUT AT A SLOW RATE, TO A PEAK OF 105 KNOTS BY TAU 48.
AFTER PASSING TAIWAN AND BEING WEAKENED BY TERRAIN INFLUENCES, THE
SYSTEM WILL CONTINUE TO WEAKEN IN THE SOUTHERN SECTION OF THE
TAIWAN STRAIT DUE TO INCREASED SHEAR AND A REDUCTION IN UPPER-LEVEL
OUTFLOW. 

MODEL DISCUSSION: THROUGH TAU 72, DETERMINISTIC MODELS ARE IN
FAIRLY GOOD AGREEMENT, WITH THE EGRR MODEL NOW THE SOLE REMAINING
OUTLIER ATTEMPTING TO TURN THE SYSTEM POLEWARD AFTER TAU 36. THE
REMAINDER OF THE TRACKERS LIE WITHIN A 85NM ENVELOPE, CENTERED ON
THE FAR SOUTHERN TIP OF TAIWAN. AFTER TAU 72, THE MODEL TRACKERS
BEGIN TO DIVERGE, SPREADING OUT ALONG BOTH THE EAST-WEST AND
NORTH-SOUTH AXES DUE TO DIFFERENCES IN HOW MUCH TERRAIN INTERACTION
THE MODELS PREDICT. THE BULK OF THE GLOBAL MODELS SHOW THE SYSTEM
CONTINUING TO MOVE FAIRLY QUICKLY TOWARDS THE WEST-SOUTHWEST,
GENERALLY TOWARDS HONG KONG, WHILE THE MESOSCALE MODELS SHOW A MORE
ERRATIC AND SLOW TRACK AFTER LANDFALL, KEEPING THE SYSTEM IN THE
TAIWAN STRAIT THROUGH TAU 120. THE LATTER IS MORE LIKELY
CONSIDERING THE COMPLEX TERRAIN INTERACTIONS AND ERRATIC MOTION
THAT CAN BE EXPECTED FROM ANY TYPHOON MAKING LANDFALL ALONG THE
SOUTHERN PORTION OF TAIWAN. THE JTWC FORECAST SLOWS DOWN AND PLACED
NEAR THE MULTI-MODEL CONSENSUS, AND THUS LAGS FAR BEHIND THE
FASTEST MODELS SUCH AS THE ECMWF AND GFS WHICH SUGGEST A POSITION
SOUTH OF HONG KONG BY TAU 120. INTENSITY GUIDANCE IS MIXED, WITH A
LARGE SPREAD IN POTENTIAL SCENARIOS, ROUGHLY BETWEEN 80 KNOTS AND
120 KNOTS. THE MORE AGGRESSIVE HWRF AND HAFS-A INDICATE THE SYSTEM
GETTING UP TO 115 KNOTS OR SO BY TAU 24, WHICH IN THEORY IS
POSSIBLE BUT SEEMS UNLIKELY DUE TO THE PRESENCE OF MID-LEVEL SHEAR
AND DRY AIR. THE OTHER MODELS INCLUDED SHIPS AND THE GFS MESOSCALE
SHOW A MUCH LOWER PEAK AT TAU 24 FOLLOWED BY STEADY WEAKENING
THROUGH THE REMAINDER OF THE FORECAST. THE JTWC REACHES THE 105
KNOT PEAK OF THE CONSENSUS, BUT ABOUT 24 HOURS LATER, THEN FOLLOWS
THE HAFS-A TRACKER AFTER TAU 72. CONFIDENCE IS LOW HOWEVER, THROUGH
THE FORECAST PERIOD DUE TO THE LACK OF CONFIRMATION THAT THE SHEAR
AND DRY AIR IS IN FACT THERE AND THE SUBSEQUENT IMPACTS ON THE
INTENSIFICATION TREND THOSE FACTORS WILL HAVE. 

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