WDPN32 PGTW 050300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 28W (HALONG) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.8N 142.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 812 NM EAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 28W IS TRACKING SLOWLY WESTWARD WITHIN A WEAK 
STEERING ENVIRONMENT. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) 
DEPICTS A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) 
POSITIONED UNDER THE WESTERN EDGE OF THE CORE CONVECTION. A 042111Z 
WSF-M 37GHZ COLOR COMPOSITE MICROWAVE IMAGE SHOWS A CURVED CONVECTIVE 
BAND ALONG THE EASTERN SEMICIRCLE, WITH EXTENSIVE DISORGANIZED 
CONVECTION DISPLACED FURTHER EAST DUE TO THE PERSISTENT WESTERLY 
VERTICAL WIND SHEAR. A 042330Z ASCAT-B BULLSEYE IMAGE REVEALS A WELL-
DEFINED, SLIGHTLY ELONGATED CENTER, WITH 30-35 KNOT WINDS OVER THE 
EASTERN AND NORTHERN QUADRANTS. THE INITIAL POSITION AND INTENSITY 
ARE PLACED WITH HIGH CONFIDENCE BASED ON THE ASCAT-B IMAGE. THE 34-
KNOT WIND RADII ARE BASED ON A DETAILED ANALYSIS OF THE ASCAT-B 
IMAGE. THE UPPER-LEVEL CIRCULATION CENTER REMAINS TILTED TO THE EAST, 
WHICH IS HINDERING SIGNIFICANT CONVECTIVE DEVELOPMENT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: COMPETING STEERING PATTERN, WITH A 
SUBTROPICAL RIDGE (STR) TO THE WEST AND ANOTHER STR TO THE EAST. A 
NARROW, WEAK BREAK IN THE STR IS PRESENT TO THE NORTH.  


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 35 KTS AT 050010Z
   CIMSS AIDT: 38 KTS AT 050010Z
   CIMSS D-PRINT: 34 KTS AT 050020Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG EASTWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM (TS) 28W IS FORECAST TO TRACK 
SLOWLY WESTWARD THROUGH TAU 24 AS THE STR BUILDS TO THE NORTH. AFTER 
TAU 24, A SERIES OF MAJOR SHORTWAVE TROUGHS WILL PROPAGATE RAPIDLY 
THROUGH THE HIGH ZONAL MIDLATITUDE WESTERLIES. HOWEVER, THESE TROUGHS 
ARE LOCATED WELL NORTH OF 45N LATITUDE AND ARE NOT EXPECTED TO IMPACT 
THE STR OR THE TS 28W TRACK. CONSEQUENTLY, THE STR SHOULD REMAIN 
ENTRENCHED TO THE NORTH DRIVING TS 28W WESTWARD TO WEST-NORTHWESTWARD 
THROUGH TAU 96. AFTER TAU 96, THE SYSTEM WILL TRACK WEST-
NORTHWESTWARD TO NORTHWARD. RAPID INTENSIFICATION (RI) IS HIGHLY 
PROBABLE AFTER TAU 24 DUE TO IMPROVING POLEWARD OUTFLOW,
ESPECIALLY AFTER TAU 48 WITH VENTING INTO THE MIDLATITUDE WESTERLIES. 
ADDITIONALLY, THE VORTEX IS FORECAST TO BECOME VERTICALLY ALIGNED 
WITHIN THE NEXT 12 HOURS. THE SYSTEM SHOULD PEAK NEAR 115 KNOTS BY 
TAU 96 AS IT APPROACHES THE RYUKYU ISLANDS.    

MODEL DISCUSSION: TRACK CONFIDENCE THROUGH TAU 120 REMAINS LOW DUE TO 
A MAJOR TRIFURCATION IN THE DETERMINISTIC GUIDANCE. THERE IS AN 
UNUSUALLY LARGE SPREAD IN DETERMINISTIC GUIDANCE, WITH A 621NM CROSS-
TRACK SPREAD AT TAU 72, 1103NM CROSS-TRACK SPREAD AT TAU 96 AND 
1678NM CROSS-TRACK SPREAD AT TAU 120. AVNI, AEMI AND JGSI CONTINUE TO 
SHOW A SHARP RECURVE TRACK COMMENCING IN THE NEXT 24 HOURS, WITH A 
POLEWARD TRACK TOWARD CENTRAL JAPAN THEN ACCELERATING EAST-
NORTHEASTWARD TRACK WELL SOUTH OF MAINLAND JAPAN. THE 041800Z RUN 
CONTINUES TO DRIVE THE SYSTEM DIRECTLY THROUGH THE SUBTROPICAL RIDGE 
DESPITE A HIGH ZONAL MIDLATITUDE PATTERN AND NO DYNAMIC SHORTWAVE 
TROUGHS. THE JTWC TRACK FORECAST FAVORS THE ECMI AND EEMI TRACKERS, 
WHICH REMAIN THE MOST STABLE AND CONSISTENT TRACKERS, WITH A WESTWARD 
TO WEST-NORTHWESTWARD TRACK OVER THE RYUKYU ISLANDS. FINALLY, AFUI, 
EGRI AND NVGI REMAIN ON THE WESTERN EDGE OF THE AIDS ENVELOPE, WITH A 
WESTWARD TRACK TOWARD TAIWAN. THIS WESTWARD TRACK IS SUPPORTED A VERY 
SMALL NUMBER OF EPS SOLUTIONS, APPROXIMATELY 15%. THE BULK OF THE EPS 
SOLUTIONS ARE CONCENTRATED IN A SWATH EXTENDING FROM OKINAWA TO ABOUT 
135E. THE 041800Z GEFS RUN ALSO SHOWS A LARGE SPREAD OF SOLUTIONS 
FANNING OUT FROM ABOUT 130E TO 142E. CONSEQUENTLY, BOTH DETERMINISTIC 
AND PROBABILISTIC GUIDANCE REFLECTS HIGH UNCERTAINTY. IN GENERAL, THE 
JTWC TRACK FORECAST CONTINUES TO FAVOR THE ECMWF SOLUTION, WITH A 
FLATTER TRACK SUPPORTED BY PERSISTENT RIDGING TO THE NORTH AND A HIGH 
ZONAL MIDLATITUDE PATTERN. DUE TO THE LARGE SPREAD IN GUIDANCE, THERE 
IS MODERATE UNCERTAINTY IN THE JTWC INTENSITY FORECAST, WITH COAMPS-
TC (GFS), HAFS-A AND GFS INDICATING A PEAK INTENSITY OF 95-135 KNOTS 
BUT WITH A SHARP RECURVE TRACK. HOWEVER, VERY FAVORABLE ENVIRONMENTAL 
CONDITIONS WILL STILL SUPPORT RAPID INTENSIFICATION WITH THE CURRENT 
JTWC TRACK FORECAST.     

FORECAST CONFIDENCE:
   TRACK 00-72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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