WDXS32 PGTW 192100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 25S (TWENTY-FIVE)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 2.3S 75.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 330 NM NORTH-NORTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
DESPITE VERY STRONG (40-50 KNOTS), PERSISTENT NORTHEASTERLY VERTICAL
WIND SHEAR (VWS) AND A LOW-LATITUDE POSITION, TROPICAL CYCLONE (TC)
25S HAS BEEN ABLE TO MAINTAIN A LIMITED AND UNIFORM AREA OF INTENSE
DEEP CONVECTION WITH CLOUD TOP TEMPERATURES COLDER THAN -88 C.
ANIMATED SHORTWAVE INFRARED (SWIR) SATELLITE IMAGERY DEPICTS A
PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION (LLC) POSITIONED ALONG THE
EASTERN EDGE OF THE DEEP CONVECTION. RECENT MICROWAVE IMAGERY
INDICATES FAIRLY WEAK LOW-LEVEL BANDING STRUCTURE. HOWEVER,
A 191653Z ASCAT-C BULLSEYE IMAGE REVEALS A DEFINED CIRCULATION WITH
A SWATH OF 30-35 KNOT WINDS OVER THE WESTERN SEMICIRCLE (VERY
ISOLATED 40 KNOT WINDS) WRAPPING INTO THE NORTHERN QUADRANT, WITH
SIGNIFICANTLY WEAKER 15-25 KNOT WINDS OVER THE EASTERN SEMICIRCLE.
BASED ON THE OVERALL LOW-LEVEL WIND FIELD, THERE IS SUFFICIENT
JUSTIFICATION FOR ASSESSING THE SYSTEM AT 35 KNOTS AND ISSUING THE
FIRST TC WARNING. SUBJECTIVE DVORAK CURRENT INTENSITY ESTIMATES OF
35 KNOTS ALSO SUPPORT THE INITIAL INTENSITY.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA

CURRENT STEERING MECHANISM: LOW-LEVEL NEAR-EQUATORIAL RIDGE (NER),
WITH ENHANCED WESTERLY FLOW.

AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 30+ KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG WESTWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TC 25S FORMED PRIMARILY DUE TO THE ENHANCED
WESTERLIES ALONG THE EQUATOR AND WILL TRACK EASTWARD THROUGH THE
FORECAST PERIOD UNDER THE ENHANCED LOW-LEVEL WESTERLY FLOW. VWS
WILL REMAIN STRONG (30-40 KNOTS) THROUGH THE FORECAST PERIOD,
LEADING TO DISSIPATION BY TAU 36 OR PERHAPS EARLIER.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN FAIR AGREEMENT
SHOWING AN EASTWARD TO SOUTHEASTWARD TRACK TRAJECTORY THROUGH TAU
36. RELIABLE INTENSITY GUIDANCE IS SPARSE LENDING MEDIUM OVERALL
CONFIDENCE TO THE JTWC INTENSITY FORECAST.

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