WDIO31 PGTW 260300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (FOUR) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 4.5N 97.9E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 645 NM SOUTHWEST OF HO CHI MINH CITY,
VIETNAM
   MOVEMENT PAST 6 HOURS: WESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
DISORGANIZED REGION OF PERSISTENT CONVECTION STRADDLING THE COAST
OF NORTHEASTERN SUMATRA. OVERSHOOTING TOPS AND VORTICAL HOT TOWERS
CONTINUE TO FLARE UP OCCASIONALLY ALONG THE COASTLINE AND IN
PROXIMITY TO THE ASSESSED LOW LEVEL CIRCULATION CENTER (LLCC) BUT
FAIL TO WRAP AROUND THE VORTEX. THE MSI ALSO SHOWS WHAT IS LIKELY
AN AREA OF TROFING EXTENDING SOUTHEASTWARD FROM THE LLCC NEAR
LANGSA, PARALLEL TO THE COAST, INDICATING THAT THE VORTEX MOST
LIKELY STRETCHED OUT AS IT APPROACHED THE COAST AND MADE LANDFALL.
RADAR DATA HAS BECOME INCREASINGLY DIFFICULT TO ANALYZE AS THE
SYSTEM APPROACHED THE COAST, BUT GENERALLY SUPPORTS A WEAK VORTEX
MOVING ASHORE WITHIN THE NEXT COUPLE OF HOURS IN THE VICINITY OF
LANGSA, INDONESIA. THE INITIAL POSITION IS ASSESSED WITH MEDIUM
CONFIDENCE BASED PRIMARILY ON ANALYSIS OF THE RADAR DATA. THE
INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, HEDGED HIGHER
THAN THE AGENCY DVORAK CURRENT INTENSITY ESTIMATES IN LIGHT OF THE
HIGHER OBJECTIVE ESTIMATES NOTED BELOW. ENVIRONMENTAL CONDITIONS
ARE DETERIORATING, WITH INCREASING EASTERLY SHEAR COMPOUNDED NOW BY
THE SYSTEM BEING OVER LAND AND STARTING TO FEEL THE ASSOCIATED
FRICTIONAL EFFECTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF THE LOW- TO
MID-LEVELS OF A DEEP SUBTROPICAL RIDGE (STR) COMPLEX TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 55 KTS AT 252330Z
   CIMSS AIDT: 42 KTS AT 260030Z
   CIMSS D-MINT: 42 KTS AT 252321Z
   CIMSS D-PRINT: 50 KTS AT 260100Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE WESTWARD
   OTHER FACTORS: LAND INTERACTION. 

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 DISCUSSED ABOVE, AVAILABLE DATA SUGGESTS
THAT THE LLCC ASSOCIATED WITH TC 04B MADE LANDFALL IN THE VICINITY
OF LANGSA AROUND 252300Z, AND SUBSEQUENTLY DRIFTED SLOWLY WESTWARD
SINCE THE 0000Z HOUR. THE SYSTEM IS FORECAST TO CONTINUE TRACKING
WESTWARD OVER THE NEXT 12 HOURS UNDER THE PRIMARY STEERING
INFLUENCE OF THE LOW- TO MID-LEVEL FLOW EMANATING FROM THE RIDGE TO
THE NORTH. THE SYSTEM WILL QUICKLY WEAKEN AS IT MOVES FURTHER
INLAND AND MOVES OVER THE MOUNTAINOUS TERRAIN OF NORTHERN SUMATRA.
AS IT DOES SO, THE MID-LEVEL VORTEX MORE THAN LIKELY WILL CONTINUE
WESTWARD, WHILE THE LLCC WILL LIKELY REACH THE RIDGELINE AND THEN
TURN SHARPLY SOUTHWARD PARALLEL TO THE RIDGELINE AXIS. HOWEVER, THE
EXACT TRACK IS SUBJECT TO AN EXTREME AMOUNT OF UNCERTAINTY, AS A TC
TRACKING THROUGH THIS PART OF THE WORLD IS EXTREMELY RARE AND THERE
IS A DEARTH OF DATA TO SUPPORT A SOLID ASSESSMENT OF THE
TERRAIN-INDUCED TRACK. EVEN IF THE MID-LEVEL VORTEX REACHES THE
INDIAN OCEAN IT IS UNLIKELY TO REDEVELOP. HENCE, THE FORECAST
TRACKS THE LLCC WHICH WILL CONTINUE TO TRACK SOUTHWARD ALONG THE
RIDGELINE THEN TURN EASTWARD AFTER TAU 24 AS STRONG WEST-SOUTHWEST
LOW-LEVEL FLOW PUSHES IN FROM THE INDIAN OCEAN AND PUSHES THE
REMNANTS OF TC 04B BACK TOWARDS THE STRAIT OF MALACCA. THE SYSTEM
IS FORECAST TO DISSIPATE OVER LAND BY TAU 36, BUT IT IS POSSIBLE
THAT THE REMNANTS COULD MOVE BACK OVER WATER AFTER TAU 36 AND A
SLIGHT CHANCE THAT THE SYSTEM COULD REDEVELOP THERE. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE HAS ACTUALLY COME
INTO MUCH BETTER AGREEMENT SINCE THE PREVIOUS FORECAST CYCLE. NOW,
THE GFS IS ONLY OUTLIER, TURNING THE SYSTEM ON A NORTHWARD ARC
AFTER TAU 12, CURVING BACK OVER THE NORTHERN PORTION OF SUMATRA
THEN BACK OVER THE NORTHERN STRAIT OF MALACCA. THE ECMWF TURNS
SOUTHEASTWARD AND TRACKS OVER THE EASTERN COAST BEFORE TURNING
EASTWARD INTO THE STRAIT, WHILE THE JTWC TRACK CLOSELY FOLLOWS THE
CONSENSUS MEAN FOR THE FORECAST DURATION, THOUGH CONFIDENCE IS LOW
DUE TO THE UNCERTAINTIES SURROUNDING THE TERRAIN INFLUENCES ON THE
TRACK FORECAST. INTENSITY GUIDANCE IS GOOD OVERALL AGREEMENT,
THOUGH IT FOR THE MOST PART SHOWS A REINTENSIFICATION AFTER TAU 36
AS THE REMNANTS MAY ENTER THE STRAIT OF MALACCA A SECOND TIME.
HOWEVER, AT THIS POINT IT IS CONSIDERED UNLIKELY THAT THE SYSTEM
WILL BE STRUCTURALLY COHERENT ENOUGH IF IT DOES MOVE BACK OVER
WATER, TO REINTENSIFY AS QUICKLY AS THE MODELS SUGGEST, SINCE THEY
DO NOT WEAKEN IT ENOUGH UP THROUGH TAU 36. THE JTWC FORECAST IS
PLACED NEAR THE CONSENSUS MEAN, BUT DEVIATES LOWER BY TAU 36 THAN
THE CONSENSUS GUIDANCE.  

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