WDXS32 PGTW 171500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN) 
WARNING NR 026//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.1S 112.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 321 NM NORTH-NORTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 18S (EIGHTEEN) WITH A SLIGHTLY IMPROVED CONVECTIVE
STRUCTURE OVER THE PAST 6 HOURS. THOUGH FLARING DEEP CONVECTIVE
BURSTS HAVE BECOME MORE PERSISTENT, THE OVERALL STRUCTURE OF THE
SYSTEM REMAINS RATHER DISORGANIZED. A 171015Z SSMIS 91 GHZ
SATELLITE MICROWAVE IMAGE REVEALS DEEP CONVECTION IN THE EASTERN
PERIPHERY OF THE LOW-LEVEL CIRCULATION CENTER (LLCC) AND CONVECTIVE 
BANDING WRAPPING INTO THE SYSTEM IN THE SOUTHERN SEMICIRCLE. THE 
CURRENT ENVIRONMENT IS ASSESSED AS MARGINAL BASED ON THE WEAK 
POLEWARD OUTFLOW ALOFT AND DRY AIR ENTRAINING INTO THE SYSTEM, WHICH 
IS OFFSET BY LOW (10-15 KTS) VERTICAL WIND SHEAR AND WARM (29-30 C)
SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH LOW
CONFIDENCE BASED ON THE AFOREMENTIONED SSMIS MICROWAVE IMAGE AND
ANIMATED EIR. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH LOW
CONFIDENCE BASED ON OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES
LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 37 KTS AT 170900Z
   CIMSS AIDT: 37 KTS AT 171200Z 

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 18S IS FORECAST TO BEGIN TRACKING SLOWLY 
SOUTHWESTWARD OVER THE NEXT 24 HOURS. AFTER TAU 24, TC 18S IS 
FORECAST TO TRACK SLOWLY NORTHWESTWARD THROUGH TAU 48 AS THE SYSTEM 
BEGINS TO FEEL THE STEERING EFFECTS OF THE SUBTROPICAL RIDGE (STR) 
THAT PROPOGATES FROM THE WEST. AS THE STR BUILDS TO THE SOUTH, THE 
STEERING MECHANISM IS EXPECTED TO BECOME MUCH MORE DEFINED AND THE 
TRACK SPEED IS ANTICIPATED TO INCREASE AS THE SYSTEM TRACKS WESTWARD 
ALONG THE NORTHERN PERIPHERY OF THE STR THROUGH THE REMAINDER OF THE 
FORECAST PERIOD. TC 18S IS FORECAST TO MAINTAIN ITS INTENSITY OF 35 
KTS UNTIL TAU 12 AND INCREASE TO 45 KTS AROUND TAU 48 DUE TO A 
DECREASE IN VERTICAL WIND SHEAR. AFTER TAU 48, TC 18S IS FORECAST TO 
BEGIN A GRADUAL INTENSIFICATION PHASE THROUGHOUT THE REMAINDER OF THE 
FORECAST PERIOD IN RESPONSE TO LOW VERTICAL WIND SHEAR AND THE VORTEX 
MOISTENING.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
REGARDING THE TRACK FORECAST. WITH THE EXCEPTION OF NAVGEM, WHICH
TRACKS THE SYSTEM SOUTHWESTWARD VICE WESTWARD, THERE IS A 110 NM
SPREAD AT TAU 72 AND A 160 NM CROSS-TRACK SPREAD AT TAU 120. THE
REST OF JTWC CONSENSUS MEMBERS FOLLOW A SIMILAR TRACK AS DESCRIBED
IN THE FORECAST DISCUSSION. THERE IS POOR AGREEMENT CONCERNING
INTENSITY GUIDANCE FOR TC 18S. HAFS-A AND HWRF BOTH SHOW THE SYSTEM
QUICKLY INTENSIFYING AFTER TAU 48 AND REACHING OVER 90 KTS BY TAU
96. CONVERSELY, COAMPS-TC CONTINUES TO KEEP TC 18S AROUND 30-45 KTS
THROUGHOUT THE FORECAST INTERVAL. AS SUCH, THE JTWC INTENSITY
FORECAST IS ASSESSED WITH OVERALL LOW CONFIDENCE. 

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