WDXS31 PGTW 180900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 05S (DARIAN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.0S 92.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 240 NM WEST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS DEEP
CONVECTION EXPANDING OVER AN INCREASINGLY TIGHTLY-WRAPPED LOW LEVEL
CIRCULATION. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
BASED ON RECENT MULTI-AGENCY SATELLITE FIXES AND A 180343Z METOP-B
ASCAT PASS. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE SAME DATASETS. TC 05S HAS CONSOLIDATED INTO
A TROPICAL CYCLONE WITH THE ENVIRONMENTAL SUPPORT OF STRONG
POLEWARD OUTFLOW AND LOW VERTICAL WIND SHEAR.

INITIAL WIND RADII BASIS: METOP-B SCATTEROMETER DATA FROM 180343Z

CURRENT STEERING MECHANISM: TRANSITIONING FROM SUBTROPICAL RIDGE
EXTENSION SITUATED TO THE SOUTHEAST TO A NEAR-EQUATORIAL RIDGE
SITUATED TO THE NORTHEAST

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

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 05S WILL TURN TOWARD AND CONTINUE ON A
SOUTHEASTWARD TRAJECTORY FOR THE NEXT 48 HOURS UNDER THE STEERING
INFLUENCE OF NEAR-EQUATORIAL RIDGING SITUATED TO THE NORTHEAST. AFTER 
TAU 48, THE NEAR-EQUATORIAL STEERING RIDGE IS EXPECTED TO WEAKEN AND
REORIENT AS A SUBTROPICAL RIDGE CONCURRENTLY BUILDS TO THE SOUTH OF
THE SYSTEM, STEERING TC 05S ON A WESTWARD TO SOUTH-WESTWARD
TRAJECTORY FOR THE REMAINDER OF THE FORECAST PERIOD. FAVORABLY LOW
VERTICAL WIND SHEAR (VWS) AND STRONG POLEWARD OUTFLOW WILL SUPPORT
STEADY INTENSIFICATION IN THE NEAR-TERM. THE MAGNITUDE OF
INTENSIFICATION SHOULD BE LIMITED, HOWEVER, AS ALONG-TRACK SEA
SURFACE TEMPERATURES ARE ONLY MARGINALLY FAVORABLE AND VWS IS
EXPECTED TO INCREASE DUE TO SHIFTING UPPER-LEVEL WINDS BY TAU 36.
INCREASING SHEAR AND A SLIGHTLY LESS FAVORABLE OUTFLOW PATTERN WILL
DRIVE WEAKENING AFTER TAU 36, BUT THE PATTERN WILL AGAIN IMPROVE
LATE IN THE FORECAST PERIOD TO SUPPORT POSSIBLE REINTENSIFICATION
BY TAU 120.

MODEL DISCUSSION: AVAILABLE NUMERICAL MODEL GUIDANCE IS IN GOOD
AGREEMENT REGARDING THE GENERAL FORECAST SCENARIO, INCLUDING A
TRACK TO THE SOUTHEAST THROUGH TAU 48 FOLLOWED BY A TURN TO THE
WEST-SOUTHWEST CONTINUING THROUGH TAU 120. SOLUTIONS VARY REGARDING
THE EXACT ORIENTATION OF THE TRACK, WHICH IS NOT SURPRISING GIVEN
THE COMPLEXITY OF CHANGES IN THE STEERING PATTERN THAT ARE
ANTICIPATED. DESPITE NOTED SPREAD, MODEL SOLUTIONS ARE FAIRLY
EVENLY DISTRIBUTED AROUND THE TRACK CONSENSUS, WHICH HAS BEEN
STEADY OVER THE PAST SEVERAL MODEL CYCLES. CONSIDERING THESE
FACTORS, OVERALL CONFIDENCE IN THE TRACK FORECAST IS MEDIUM.
INTENSITY FORECAST GUIDANCE IS ALSO IN GOOD AGREEMENT WITH RESPECT
TO THE GENERAL TREND - UPWARD IN THE NEAR TERM, FOLLOWED BY
WEAKENING AFTER TAU 36 AND THE POSSIBILITY OF SLOW
REINTENSIFICATION BY TAU 120. A FEW MODELS, INCLUDING THE COAMPS-TC
ENSEMBLE AND A STATISTICAL-DYNAMICAL RAPID INTENSIFICATION AID,
INDICATE THE POSSIBILITY OF MORE PRONOUNCED INTENSIFICATION IN THE
NEAR-TERM, BUT THE HWRF AND SHIPS SOLUTIONS ARE MORE MUTED. GIVEN
THE ENVIRONMENTAL FACTORS NOTED ABOVE, RAPID INTENSIFICATION DOES
NOT SEEM LIKELY AT THIS POINT. CONFIDENCE IN THE INTENSITY FORECAST
IS MEDIUM.

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