WDXS31 PGTW 021500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04S (ALVARO) WARNING 
NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.1S 47.5E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 192 NM SOUTH OF ANTANANARIVO, MADAGASCAR
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: XX FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT TROPICAL
CYCLONE (TC) 04S (ALVARO) HAS UNDERGONE RAPID VORTEX DECOUPLING,
WITH A RAGGED LOW LEVEL CIRCULATION CENTER (LLCC) NOW VISIBLE WEST
OF THE NORTH-SOUTH ORIENTED TERRAIN FEATURES, WHILE THE MID-LEVEL
VORTICITY CENTER AND ASSOCIATED CONVECTION CONTINUES TO PUSH OFF TO
THE EAST. A 021047Z ATMS 165GHZ MICROWAVE IMAGE SHOWED WEAK
LOW-LEVEL BANDING FEATURES DISPLACED TO THE WEST OF AN AREA OF
SYMMETRICAL CONVECTION, WHICH MARKS THE EASTERN VORTICITY LOBE. THE
INITIAL POSITION IS PLACED CLOSER TO THE MID-LEVEL VORTICITY
CENTER, ON THE WESTERN SIDE OF THE CONVECTION, IN ANTICIPATION OF A
RAPID REDEVELOPMENT UNDER THE MID-LEVEL ROTATION ONCE IT REACHES
THE EAST COAST. SURFACE OBSERVATIONS FROM FARAFANGANA, ALONG THE
EAST COAST, REPORT SURFACE WINDS FROM THE SOUTHEAST AT 14 KNOTS,
SUGGESTING A LOW-LEVEL ROTATION MAY ALREADY BE DEVELOPING TO THE
NORTH OF THE STATION, AND PROVIDING SOME MODEST SUPPORT TO THE
PLACEMENT OF THE INITIAL POSITION. OVERALL HOWEVER, THE INITIAL
POSITION IS ASSESSED WITH LOW CONFIDENCE. THE INITIAL INTENSITY IS
LIKEWISE SET WITH LOW CONFIDENCE DUE TO THE LACK OF SATELLITE-BASED
INTENSITY ESTIMATES, WITH THE LONE EXCEPTION OF THE CIMSS DPRINT,
AT 37 KNOTS. AS MENTIONED ABOVE, THE SYSTEM HAS DECOUPLED AND THE
BEST TRACK IS TRACKING THE EASTERN, MOSTLY MID-LEVEL, ROTATION
LEADING TO A TRACK SPEED OF 12 KNOTS TOWARDS THE EAST-SOUTHEAST
ALONG THE SOUTHWESTERN PERIPHERY OF A DEEP-LAYER NEAR EQUATORIAL
RIDGE (NER) CENTERED TO THE NORTHEAST. ANALYSIS REVEALS A
MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE TO
STRONG POLEWARD OUTFLOW OFFSET BY 20-25 KNOTS OF WESTERLY SHEAR THE
INFLUENCE OF TERRAIN.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
NER TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: OVER LAND
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: LOW
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 04S IS FORECAST TO TRACK SOUTHEASTWARD
ALONG THE SOUTHERN SIDE OF THE NER THROUGHOUT THE SHORT DURATION OF
THE FORECAST PERIOD, WITH SOME ACCELERATION AFTER TAU 12 AS THE
GRADIENT TIGHTENS BETWEEN THE NER AND A TROUGH TO THE SOUTH. THE
MID-LEVEL VORTICITY ASSOCIATED WITH THE EASTERN LOBE OF A FULLY
DECOUPLED TC 04S, IS SET TO EMERGE BACK OVER WATER OFF THE EASTERN
COAST OF MADAGASCAR WITHIN THE NEXT FEW HOURS. ONCE THIS OCCURS, A
RAPID, TOP-DOWN REDEVELOPMENT IS ANTICIPATED, TAKING ADVANTAGE OF A
BRIEF WINDOW OF SLIGHTLY LOWER VERTICAL WIND SHEAR (VWS), WARM SSTS
APPROACHING 28C AND STRONG POLEWARD OUTFLOW, ALLOWING THE SYSTEM TO
REINTENSIFY UP TO 40 KNOTS BY TAU 12. SHEAR IS EXPECTED TO REMAIN
NEAR 20 KNOTS THROUGH ABOUT TAU 24 BEFORE RAPIDLY INCREASING TO
VERY HIGH LEVELS. THE RAPID INCREASE IN WEST-NORTHWESTERLY SHEAR WILL
ALSO USHER IN A VERY DRY AIR MASS. THE COMBINED EFFECTS OF THE
INCREASED SHEAR AND DRY AIR WILL DECAPITATE THE SYSTEM AND SMOTHER
THE REMAINING LOW-LEVEL CIRCULATION AFTER TAU 24, LEADING TO RAPID
WEAKENING AND DISSIPATION BY TAU 48. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN VERY TIGHT
AGREEMENT, WITH THE ENTIRE CONSENSUS PACKAGE CONFINED TO A 60NM
CROSS-TRACK ENVELOPE AT TAU 48. THE JTWC FORECAST LIES CLOSE TO THE
MULTI-MODEL CONSENSUS MEAN WITH HIGH CONFIDENCE. INTENSITY GUIDANCE
IS MIXED, WITH THE COAMPS-TC (GFS VERSION) AND HAFS-A MODELS
SUGGESTING RAPID INTENSIFICATION BY TAU 12, WITH PEAKS BETWEEN 50
KTS TO 60 KTS, WHILE THE SHIPS AND GFS GUIDANCE SHOW THE SYSTEM
BARELY REACHING 35 KTS WITHIN THE FIRST 24 HOURS. THE JTWC FORECAST
TRACKS THE CONSENSUS MEAN THROUGH TAU 24, THEN DISSIPATES THE
SYSTEM MORE IN LINE WITH THE SHIPS GUIDANCE, WITH LOW CONFIDENCE. 

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