WDXS32 PGTW 130900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN)
WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.9S 110.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 482 NM NORTH-NORTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS TROPICAL CYCLONE
(TC) 18S AS HAVING TWO MESOVORTICES ROTATING ABOUT A CENTROID AS
SHOWN IN A 122245Z SSMIS 91 GHZ SATELLITE MICROWAVE IMAGE. A
130223Z ASCAT-C IMAGE REVEALS 30 KTS, REASONABLY 35KTS INCORPORATING 
A GENERAL LOW BIAS OF THE COLLECTING SENSOR, ASSOCIATED WITH BOTH OF
THE MESOVORTICES IN THEIR NORTHERN PERIPHERY AND 15-20 KTS WINDS
IN THEIR SOUTHERN SEMICIRCLE. ENVIRONMENTAL ANALYSIS INDICATES
THAT TC 18S IS IN A MARGINALLY FAVORABLE ENVIRONMENT FOR FURTHER
INTENSIFICATION WITH MODERATE POLEWARD OUTFLOW ALOFT AND WARM
(29-30 C) SEA SURFACE TEMPERATURES OFFSET BY HIGH (25-30 KTS)
VERTICAL WIND SHEAR. THE INITIAL POSITION IS PLACED WITH LOW
CONFIDENCE BASED ON A 130600Z HIMAWARI-9 SATELLITE VISIBLE IMAGE. THE 
INITIAL INTENSITY IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE 
AFOREMENTIONED SCATTEROMETRY DATA.

INITIAL WIND RADII BASIS: SCATTEROMETRY DATA 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A NEAR EQUATORIAL
RIDGE (NER) TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 35 KTS AT 130700Z
   CIMSS ADT: 31 KTS AT 130800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 25-30 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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: TC 18S IS CURRENTLY TRACKING SOUTHEASTWARD
ALONG THE SOUTHERN PERIPHERY OF A NER TO THE NORTH. TC 18S IS
FORECAST TO CONTINUE THIS TRACK THROUGH TAU 48 WHERE IT WILL COMMENCE 
A SOUTHWESTWARD TURN THROUGH TAU 72 DUE TO A STR ANCHORED OVER 
WESTERN AUSTRALIA. THE SYSTEM IS FORECAST TO CONTINUE ON A 
SOUTHWESTWARD TRACK OVER THE REMAINDER OF THE FORECAST PERIOD. 
REGARDING THE INTENSITY FORECAST, TC 18S IS FORECAST TO MAINTAIN 35 
KTS THROUGH TAU 12 AND INCREASE SLIGHTLY TO 40 KTS BY TAU 24 IN A 
MARGINALLY FAVORABLE ENVIRONMENT. AFTER TAU 24, VERTICAL WIND SHEAR IS 
ANTICIPATED TO DECREASE TO UNDER 10 KTS BY TAU 36, WHICH WILL START 
AN EVIDENT INTENSIFYING TREND OVER THE REMAINDER OF THE FORECAST 
PERIOD. THE SYSTEM IS FORECAST TO REACH AN INTENSITY OF NEAR 80 KTS 
BY TAU 120.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
WITH A 250 NM CROSS-TRACK SPREAD AT TAU 72. GFS CONTINUES TO BE THE 
OUTLYING MODEL OF CONSENSUS MEMBERS TRACKING THE SYSTEM FURTHER 
EASTWARD BEFORE MAKING THE SOUTHWESTWARD TURN. THE JTWC FORECAST IS 
CLOSER TO ECMWF DETERMINISTIC AND ENSEMBLE MODEL SOLUTIONS. 
CONSIDERING THE LARGE SPREAD IN GUIDANCE, THE JTWC TRACK FORECAST IS 
PLACED WITH OVERALL LOW CONFIDENCE. THE INTENSITY GUIDANCE IS IN 
SLIGHTLY BETTER ALIGNMENT SUGGESTING A GRADUAL INCREASE OVER THE 
FORECAST PERIOD. WITH THE EXCEPTION OF COAMPS-TC, GUIDANCE AGREES 
THAT THE SYSTEM WILL REACH AN INTENSITY OF 80KTS WITH AN INTENSITY 
SPREAD RANGING BETWEEN 65 TO 85 KTS AT TAU 120. 

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