WDXS31 PGTW 170900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 01S (ONE) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.9S 88.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 982 NM EAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD, 
EXPOSED LOW-LEVEL CIRCULATION, WITH PERSISTENT DEEP CONVECTION SHEARED 
TO THE SOUTH AND SOUTHWEST. THIS WEAK STRUCTURE IS ALSO EVIDENT IN A 
170716Z ATMS 88.2GHZ MICROWAVE IMAGE, WITH A SYMMETRIC AREA OF DEEP 
CONVECTION WELL SOUTH OF THE LOW-LEVEL CIRCULATION CENTER. A 170306Z 
ASCAT-C BULLSEYE IMAGE REVEALS A DEFINED CENTER, WITH 30-35 KNOT WINDS 
OVER THE SOUTHERN QUADRANT, WHICH SUPPORTS THE INITIAL POSITION AND 
INTENSITY WITH HIGH CONFIDENCE. ASCAT IMAGERY ALSO CONFIRMS THAT GALE 
FORCE WINDS ARE CONFINED TO THE SOUTHERN SEMICIRCLE. ENVIRONMENTAL 
CONDITIONS ARE MARGINALLY FAVORABLE DUE TO LOW TO MODERATE MID-LEVEL 
EAST-NORTHEASTERLY VERTICAL WIND SHEAR (VWS) OFFSET BY MODERATE 
POLEWARD OUTFLOW AND WARM SST VALUES.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
POSITIONED TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   DEMS: T2.0 - 30 KTS
   FMEE: T2.0 - 30 KTS
   CIMSS ADT: 34 KTS AT 170615Z
   CIMSS AIDT: 32 KTS AT 170515Z
   CIMSS D-PRINT: 25 KTS AT 170615Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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 CYCLONE (TC) 01S WILL TRACK WEST-
SOUTHWESTWARD THROUGH TAU 36 ALONG THE NORTHERN PERIPHERY OF THE LOW- 
TO MID-LEVEL SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTH. VWS IS 
FORECAST TO ABATE BRIEFLY FROM TAU 24 TO TAU 36, WHICH WILL SUPPORT 
MODEST INTENSIFICATION TO A PEAK INTENSITY OF 40 KNOTS. AFTER TAU 36, 
THE WESTERN PORTION OF THE STR WILL WEAKEN AND REORIENT WITH THE 
APPROACH OF A DEEP UPPER-LEVEL TROUGH, WHICH WILL ALLOW TC 01S TO TURN 
SOUTHWESTWARD THROUGH TAU 48. SLIGHT WEAKENING IS EXPECETD AS VWS 
INCREASES TO MODERATE LEVELS. AFTER TAU 48, THE AFOREMENTIONED UPPER-
LEVEL TROUGH WILL FILL ALLOWING THE STR TO BUILD BACK IN TO THE SOUTH. 
THE SYSTEM WILL GRADUALLY WEAKEN AS IT TRACKS OVER COOLER SST VALUES 
(25C) AND ENTRAINS DRY AIR, WITH DISSIPATION ANTICIPATED BY TAU 72.       

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 36, WITH A 60NM CROSS-TRACK SPREAD AT TAU 36. GUIDANCE
DIVERGES AFTER THIS TIME AS THE STEERING ENVIRONMENT EVOLVES QUICKLY. 
THE 170000Z GEFS RUN SHOWS A SIMILAR SPREAD OF SOLUTIONS, SUPPORTING 
THE DISSIPATION SCENARIO, WITH THE MAJORITY OF SOLUTIONS BELOW 35 
KNOTS WEST OF 80E LONGITUDE. RELIABLE INTENSITY GUIDANCE SUPPORTS A 
BRIEF INTENSIFICATION PHASE, WITH COAMPS-TC (GFS AND NAVGEM) SHOWING A 
PEAK INTENSITY NEAR 43 KNOTS FROM TAU 24 TO TAU 48. HAFS-A IS A BIT 
MORE PESSIMISTIC, WITH A PEAK INTENSITY OF 37 KNOTS AT TAU 12. 

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