WDPN32 PGTW 220300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 05W (GAEMI) WARNING NR 
010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.6N 125.9E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 513 NM SOUTH-SOUTHEAST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 05W (GAEMI) CONTINUES TO EXHIBIT CYCLING DEEP
CONVECTIVE BURSTS, WHICH FAIL TO PERSIST IN THE FACE OF PERSISTENT,
MODERATE NORTHEASTERLY SHEAR. OVER THE PAST COUPLE OF DAYS, STRONG
CONVECTIVE BURSTS WILL FLARE UP NEAR THE LOW LEVEL CIRCULATION
CENTER (LLCC), ONLY TO QUICKLY FADE AWAY AFTER BEING SHEARED OFF TO
THE SOUTHWEST. THE LATEST CIMSS SHEAR ESTIMATE IS 16 KNOTS FROM THE
NORTH-NORTHEAST, WHICH ALIGNS WELL WITH THE SATELLITE DEPICTION OF
A PARTIALLY EXPOSED LLCC TUCKED UNDER THE EXTREME NORTHEAST EDGE OF
THE CENTRAL DENSE OVERCAST (CDO) FEATURE. A 212150Z SSMIS 91GHZ
MICROWAVE IMAGE PROVIDED GOOD EVIDENCE THAT THE LLCC IS NOT ALIGNED
WITH THE UPPER-LEVEL CONVECTION. THE INITIAL POSITION WAS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION OF THE LLCC SEEN IN
THE MICROWAVE IMAGERY NOTED ABOVE AND ANALYSIS OF THE OUTER RAIN
BANDS SEEN IN THE DRY AIR TO THE NORTHEAST OF THE CDO. REANALYSIS
OF AVAILABLE INTENSITY DATA RESULTED IN A DOWNWARD ADJUSTMENT OF THE
1800Z INTENSITY TO 50 KNOTS. THE INITIAL INTENSITY AT 0000Z WAS
KEPT STEADY AT 50 KNOTS, WITH MEDIUM CONFIDENCE, HEDGED SLIGHTLY
LOWER THAN THE AGENCY DVORAK ESTIMATES, IN LIGHT OF THE OBJECTIVE
ESTIMATES WHICH ARE ALL AT OR BELOW 50 KNOTS. THE ENVIRONMENT
REMAINS OVERALL FAVORABLE, WITH VERY WARM, HIGH OHC WATERS, GOOD
EQUATORWARD AND MODERATE POLEWARD OUTFLOW, OFFSET BY THE MODERATE
SHEAR. MODEL CROSS SECTIONS SHOW A WEDGE OF DRY AIR, PARTICULARLY
TO THE NORTHEAST OF THE LLCC, WHICH IS SUPPORTED BY THE LACK OF
SIGNIFICANT CONVECTIVE ACTIVITY IN THAT SECTOR IN THE MSI. UNTIL
THIS DRY AIR MOVES OUT, ANY CONVECTION THAT DOES FORM IS UNLIKELY
TO BE ABLE TO EXPAND FAR ENOUGH NORTHEASTWARD TO OFFSET THE SHEAR
VECTOR. THE SYSTEM HAS STARTED TO SLOWLY DRIFT NORTHWARD AT ABOUT
FOUR KNOTS AS THE BUBBLE ANTICYCLONE ALOFT STARTS TO SHIFT
SOUTHWESTWARD AND OPEN UP AN AVENUE FOR THE SYSTEM TO TRACK
NORTHWARD.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN SIDE OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE EAST AND A WEAKENING BLOCKING
ANTICYCLONE TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 45 KTS AT 212000Z
   CIMSS ADT: 49 KTS AT 220000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY AIR TO THE NORTH AND EAST. 

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: AS THE UPPER-LEVEL BLOCKING ANTICYCLONE THAT
HAS BEEN KEEPING TS 05W IN A RELATIVELY QUASI-STATIONARY POSITION
OVER THE LAST 24 HOURS BEGINS TO SHIFT SOUTHWESTWARD, TS GAEMI WILL
START TO ACCELERATE NORTHWARD OVER THE NEXT 12 HOURS. THE
ANTICYCLONE WILL BE COMPLETELY OUT OF THE PICTURE WITHIN 18 HOURS
AND A WEAKNESS IN THE STR TO NORTH WILL OPEN UP, PRESENTING TS 05W
WITH A WIDE-OPEN AVENUE POLEWARD. THE SYSTEM WILL TRACK
NORTH-NORTHWESTWARD THROUGH TAU 36, BEFORE THE STR BUILDS AND
EXTENDS IN TO THE NORTH, ROUGHLY ALONG A LINE FROM SOUTH OF TOKYO
TO SHANGHAI. TS 05W WILL TURNS NORTHWEST AFTER TAU 36, PASS SOUTH
OF ISHIGAKIJIMA AFTER TAU 48, THEN CLIP THE NORTHEAST COAST OF
TAIWAN AROUND TAU 72. AFTER MAKING LANDFALL ON THE NORTHERN TIP OF
TAIWAN, THE SYSTEM CROSSES THE TAIWAN STRAIT AND MAKES A SECOND
LANDFALL OVER EASTERN CHINA AROUND TAU 84, BEFORE MOVING DEEPER
INTO EASTERN CHINA. SHEAR IS EXPECTED TO REMAIN ELEVATED FOR
ANOTHER 12 HOURS BEFORE DROPPING OFF SHARPLY BY TAU 18. ONCE THIS
HAPPENS, RAPID AXISYMMETRIZATION AND VORTEX ALIGNMENT IS EXPECTED.
AT THE SAME TIME, THE SYSTEM WILL BE MOVING OVER A POOL OF HIGH
(110-120 KJ PER CM2) WATERS, WHICH WILL TOUCH OFF A PERIOD OF RAPID
INTENSIFICATION (RI) BETWEEN TAU 24 AND TAU 48. PEAK INTENSITY IS
EXPECTED TO BE AROUND 95 KNOTS AT TAU 48, THOUGH A SLIGHTLY HIGHER
PEAK IS POSSIBLE BEFORE THE SYSTEM PASSES THE RYUKYU ISLANDS. SHEAR
BEGINS TO INCREASE ONCE MORE AFTER TAU 60, AND REALLY PICKS UP BY
TAU 72, AS THE SYSTEM REACHES TAIWAN. INTERACTION WITH THE COMPLEX
AND ELEVATED TERRAIN OF TAIWAN AND THE HIGH SHEAR WILL RAPIDLY
WEAKEN THE SYSTEM BEFORE IT MAKES LANDFALL IN EASTERN CHINA. ONCE
OVER LAND THE SYSTEM QUICKLY DISSIPATES BY THE END OF THE FORECAST
PERIOD. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH THE
ENTIRE FORECAST PERIOD, WITH A CROSS-TRACK SPREAD OF 165NM AT TAU
72. THE GFS AND NAVGEM TRACKERS MARK THE SOUTHERN EDGE OF THE
GUIDANCE ENVELOPE, SHOWING THE SYSTEM MAKING LANDFALL ALONG THE
EAST COAST OF TAIWAN NEAR 24N. THE ECMWF TRACKER MARKS THE NORTHERN
EDGE, KEEPING THE CENTER OFF THE NORTHEAST COAST OF TAIWAN.  AFTER
TAU 72, THE GUIDANCE SPREAD INCREASES SOMEWHAT, BUT STILL AGREES ON
THE OVERALL TRACK SOLUTION. THE JTWC FORECAST IS BASED ON A BLEND
OF THE GFS AND ECMWF, THOUGH HEDGED TOWARDS THE ECMWF SOLUTION,
SINCE ECMWF HAS SHOWN TO HAVE INITIALIZED THE BEST OVER THE LAST
TWO RUNS, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN FAIR
AGREEMENT, WITH THE BULK OF THE MODELS SHOWING A FLAT OR SLIGHT
INTENSIFICATION THROUGH TAU 12, FOLLOWED BY NEAR-RAPID, TO RAPID
INTENSIFICATION. THE JTWC PEAK IS ABOUT FIVE KNOTS HIGHER THAN THE
HAFS-A AND HWRF SOLUTIONS BUT OTHERWISE IS CONSISTENT WITH THE
OVERALL SHAPE OF THE INTENSITY TREND. 

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