WDXS31 PGTW 040900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 25S (TWENTYFIVE) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.7S 109.4E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 691 NM NORTH-NORTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: EASTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 25S WITH A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC) AND DEEP CONVECTION HEAVILY SHEARED OFF TO THE WEST. THE
PERSISTENT EASTERLY SHEAR HAS CONTINUED TO CAUSE THE MID-LEVEL
CIRCULATION TO BE OFFSET TO THE WEST OF THE SURFACE CIRCULATION.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
LOW-LEVEL CLOUD TRACING IN THE ANIMATED MSI. THE INITIAL INTENSITY
OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED PRIMARILY ON THE
AGENCY DVORAK FIXES OF T2.5. ENVIRONMENTAL ANALYSIS INDICATES THAT
25S IS IN A MARGINAL ENVIRONMENT CHARACTERIZED BY MODERATE POLEWARD
OUTFLOW ALOFT, HIGH (25-30 KTS) EASTERLY VERTICAL WIND SHEAR, AND
WARM SEA SURFACE TEMPERATURES (29-30 C).

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: A NEAR-EQUATORIAL RIDGE (NER)
POSITIONED TO THE NORTH

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

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

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 25S IS FORECAST TO TRACK EASTWARD, ALONG
THE SOUTHERN PERIPHERY OF THE NER TO THE NORTH, THROUGH TAU 24.
NEAR TAU 24, INTERACTION WITH THE WIND FIELD OF A SEPARATE
DEVELOPING LOW PRESSURE AREA (93S) TO THE SOUTH WILL CAUSE 25S TO
TURN SOUTHEASTWARD. REGARDING INTENSITY, 25S IS FORECAST TO
MARGINALLY INTENSIFY OVER THE NEXT 24 HOURS AS STRONG EASTERLY 
SHEAR CONTINUES TO IMPACT THE VORTEX, DISALLOWING FURTHER
INTENSIFICATION. AFTER TAU 24, THE SYSTEM WILL BEGIN WEAKENING AS
THE VORTEX SHALLOWS OUT WITH INCREASING DRY AIR ENTRAINMENT FROM
THE WEST AND EASTERLY SHEAR OF OVER 40 KTS. 25S IS EXPECTED TO
DISSIPATE AROUND TAU 48, NORTHWEST OF BROOME.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN MODERATE
AGREEMENT WITH A 140 NM CROSS-TRACK SPREAD AT TAU 48. THE JTWC
TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS AND
ECMWF ENSEMBLE MEAN TRACKERS THROUGHOUT THE FORECAST PERIOD WITH
MEDIUM CONFIDENCE. INTENSITY GUIDANCE GENERALLY AGREES ON MARGINAL
INTENSIFICATION THROUGH TAU 12-24 FOLLOWED BY WEAKENING. HAFS-A IS
SLIGHTLY MORE RELUCTANT TO WEAKEN THE SYSTEM THAN THE REMAINDER OF
GUIDANCE, SUGGESTING AN INTENSITY OF AROUND 35 KTS THROUGH TAU 96.
THE JTWC INTENSITY FORECAST IS PLACED NEAR THE CONSENSUS WITH
MEDIUM CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM//
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