WDXS31 PGTW 031500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04S (ALVARO) WARNING 
NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.2S 51.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 299 NM SOUTHWEST OF ST DENIS
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT TC 04S
(ALVARO) IS RAPIDLY DETERIORATING UNDER PERSISTENT
WEST-NORTHWESTERLY SHEAR. THE LATEST IMAGERY SHOWS A RAGGED AND
ILL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) NO FULLY EXPOSED TO
THE NORTHWEST OF AN AREA OF DEEP PERSISTENT CONVECTION. A 031015Z
AMSR2 36GHZ MICROWAVE IMAGE SHOWS THE LLCC JUST NORTHWEST OF THE
HEAD OF A COMMA-SHAPED REGION OF CONVECTIVE ACTIVITY, SUGGESTIVE OF
THE ONSET OF SUBTROPICAL TRANSITION. THE INITIAL POSITION IS
ASSESSED WITH HIGH CONFIDENCE BASED ON AN EXTRAPOLATION OF THE LLCC
SEEN IN THE MICROWAVE IMAGERY AS WELL AS THE EXPOSED LLCC IN THE
MSI. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED
ON AN OVERALL AVERAGE OF AVAILABLE SUBJECTIVE AND OBJECTIVE
INTENSITY ESTIMATES OUTLINED BELOW. THE SYSTEM IS IN AN UNFAVORABLE
ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD OUTFLOW INTO A
SUBTROPICAL JET MAX TO THE SOUTHEAST, BEING OFFSET BY MID-LEVEL DRY
AIR ENTRAINMENT, STRONG WESTERLY VERTICAL WIND SHEAR (VWS) AND
STEADILY DECREASING SSTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
NEAR EQUATORIAL RIDGE (NER) - SUBTROPICAL RIDGE (STR) EXTENDING
FROM NORTH OF A MADAGASCAR TO EAST OF MAURITIUS. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   FMEE: T3.5 - 55 KTS
   CIMSS SATCON: 44 KTS AT 031130Z
   CIMSS ADT: 43 KTS AT 030900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MID-LEVEL DRY AIR PUSHING IN FROM THE WEST. 

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING OTHER THAN THE FORECAST
DURATION, WHICH IS NOW TRUNCATED TO 36 HOURS. 

FORECAST DISCUSSION: TC 04S WILL CONTINUE TRACKING SOUTHEASTWARD
THROUGH THE DURATION OF THE SHORT FORECAST PERIOD, ALONG THE
SOUTHERN PORTION OF THE STEERING RIDGE COMPLEX. A SLIGHT SLOWDOWN
IS EXPECTED BY THE END OF THE FORECAST AS THE STEERING GRADIENT
LOOSENS UP A BIT. HAVING NOW BEEN OVERCOME BY THE STRONG WESTERLY
SHEAR, THE VORTEX HAS DECOUPLED WITH THE LOW-LEVEL VORTEX NOW FULLY
EXPOSED. THE STRONG WESTERLY FLOW WILL PUSH IN A WEDGE OF VERY DRY
AIR IN THE MID-LEVELS, AND EFFECTIVELY SQUASH ANY HOPE OF FURTHER
INTENSIFICATION. THE REAL QUESTION IS WHICH WILL OCCUR FIRST;
SUBTROPICAL TRANSITION (STT), OR DISSIPATION. STT HAS LIKELY
ALREADY STARTED AS THE SYSTEM IS BEGINNING TO INTERACT WITH THE
STRONG SUBTROPICAL WESTERLIES AND BEGINS TO MOVE OVER COOLER
WATERS, BUT THE RECENT DECOUPLING MEANS THAT THE SYSTEM WILL WEAKEN
RELATIVELY QUICKLY. THE RESULT IS THAT TC 04S WILL LIKELY DISSIPATE
BELOW THE WARNING THRESHOLD WHILE SIMULTANEOUSLY COMPLETING STT.
REGARDLESS, THE SYSTEM WILL NO LONGER BE A TROPICAL CYCLONE WITHIN
THE NEXT 24 TO 36 HOURS. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN VERY TIGHT
AGREEMENT, WITH MINIMAL ALONG AND CROSS-TRACK SPREAD, PROVIDING
HIGH CONFIDENCE TO THE JTWC FORECAST TRACK. INTENSITY GUIDANCE IS
MIXED, WITH THE BULK OF THE GUIDANCE PACKAGE INDICATING
INTENSIFICATION UP TO 50 KNOTS, WITH THE NOTABLE EXCEPTION OF THE
DECAY SHIPS (BOTH GFS AND NAVGEM VERSIONS) WHICH ARE THE SOLE
OUTLIERS SHOWING STEADY WEAKENING AND DISSIPATION WITHIN 24 TO 36
HOURS. THE JTWC FORECAST IS GENERALLY CONSISTENT WITH THE MULTI-MODEL
CONSENSUS MEAN THROUGH THE FORECAST PERIOD, WITH MEDIUM CONFIDENCE.


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