WDXS32 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 15S (EWETSE) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.6S 41.3E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 213 NM SOUTH-SOUTHEAST OF EUROPA ISLAND
   MOVEMENT PAST 6 HOURS: EASTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 15S (EWETSE) HAS UNDERGONE RAPID CYCLOGENESIS 
OVER THE LAST 24 HOURS FOLLOWING EMERGENCE INTO THE SOUTHERN 
MOZAMBIQUE CHANNEL. THE SYSTEM IS SITUATED ALONG THE TAIL END OF A 
REMNANT SHEAR LINE WHICH EXTENDS FAR TO THE SOUTHEAST, OFF THE 
SOUTHERN COAST OF MADAGASCAR. ANIMATED ENHANCED INFRARED (EIR) 
SATELLITE IMAGERY DEPICTS A COMPACT CENTRAL DENSE OVERCAST (CDO) 
FEATURE, WITH CYCLONIC ROTATION EVIDENT IN THE OVERSHOOTING TOPS 
ALONG THE NORTHERN QUADRANT OF THE CDO. A LACK OF CONCURRENT 
MICROWAVE IMAGERY PRECLUDED A HIGH CONFIDENCE ASSESSMENT OF THE LOW-
LEVEL STRUCTURE AND PLACEMENT OF THE LOW-LEVEL CIRCULATION CENTER 
(LLCC) AT SYNOPTIC ANALYSIS TIME. SUBSEQUENTLY, A LATE-BREAKING ASCAT 
PASS FROM 201850Z INDICATES A COMPACT, SYMMETRICAL LLCC DISPLACED 
APPROXIMATELY ONE DEGREE NORTHWARD OF THE ANALYZED BEST TRACK 
POSITION (NEAR 24.6S 41.7E). THE ASCAT DATA ALSO REVEALS PEAK 
MAGNITUDES OF 45-50 KNOTS IN THE SOUTHWESTERN PERIPHERY OF THE LLCC. 
LATE RECEIPT OF A 201448Z SMOS PASS ALSO SUPPORTS AN INTENSITY 
APPROXIMATING 50 KNOTS; ACCORDINGLY, BOTH POSITION AND INTENSITY 
METRICS WILL BE REVISED IN POST-ANALYSIS TO REFLECT THESE EMPIRICAL 
DATASETS. ENVIRONMENTAL CONDITIONS ARE CONDUCIVE TO ADDITIONAL 
INTENSIFICATION, CHARACTERIZED BY LOW TO MODERATE DEEP-LAYER VERTICAL 
WIND SHEAR (VWS), OPTIMAL SSTS, AND ROBUST POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: LOW-LEVEL WESTERLY FLOW ON THE
EQUATORWARD SIDE OF A LOW-LEVEL SHEAR LINE WHICH EXTENDS SOUTHEAST
TO THE SOUTH OF MADAGASCAR. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   FMEE: T2.5 - 35 KTS
   CIMSS D-PRINT: 38 KTS AT 201800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 15S CONSOLIDATED RAPIDLY OVER THE LAST 12 
HOURS, EXHIBITING ACCELERATED INTENSIFICATION OVER THE PAST SIX HOURS 
WHILE TRACKING EASTWARD. THE SYSTEM WILL MAINTAIN AN EASTERLY 
TRAJECTORY ALONG THE NORTHERN FLANK OF A BAND OF LOW-LEVEL WESTERLY 
FLOW ON THE EQUATORWARD SIDE OF A REMNANT SHEAR LINE, WHICH IS ITSELF 
PUSHING EASTWARD. LANDFALL IS ANTICIPATED ALONG THE SOUTHWESTERN 
COAST OF MADAGASCAR NEAR TAU 12, FOLLOWED BY AN INLAND TRACK 
NORTHWARD ALONG THE OROGRAPHIC SPINE OF THE CENTRAL MOUNTAINS THROUGH 
THE REMAINDER OF THE FORECAST PERIOD. IN TERMS OF INTENSITY, THE 
FORECAST INDICATES AN ADDITIONAL INTENSIFICATION OF 5-10 KNOTS PRIOR 
TO IMPACT, WITH THE OFFICIAL FORECAST INDICATING LANDFALL AS A 45-
KNOT TROPICAL CYCLONE. HOWEVER, BASED UPON INTEGRATED DATA SUPPORTING 
A HIGHER INITIAL INTENSITY, PEAK INTENSITY IS LIKELY TO REACH 55-60 
KNOTS. REGARDLESS, FOLLOWING LANDFALL, THE SYSTEM WILL UNDERGO RAPID 
DECAY DUE TO FRICTIONAL EFFECTS OVER THE RUGGED TERRAIN, RESULTING IN 
FULL DISSIPATION BY TAU 36.

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN STRONG
AGREEMENT, SUPPORTING AN EASTWARD TRACK AND LANDFALL ALONG THE
SOUTHWESTERN COAST OF MADAGASCAR WITHIN THE NEXT 12-15 HOURS. POST-
LANDFALL, THE MODEL SUITE EXHIBITS SIGNIFICANT DIVERGENCE; TRACKERS 
DISPERSE RAPIDLY, WITH BIFURCATION BETWEEN MODELS SHOWING A RE-
EMERGENCE INTO THE MOZAMBIQUE CHANNEL VERSUS A ZONAL CROSSING INTO 
THE SOUTH INDIAN OCEAN. THE MAJORITY OF OBJECTIVE GUIDANCE DEPICTS A 
POLEWARD TRACK ALONG THE MOUNTAIN SPINE, SUCCEEDED BY A CYCLONIC 
RECURVATURE TO THE WEST. THE JTWC TRACK IS ALIGNED WITH THE MULTI-
MODEL CONSENSUS MEAN WITH HIGH CONFIDENCE. HOWEVER, THE REVISION IN 
INITIAL POSITION WILL NECESSITATE A NORTHWARD SHIFT IN THE LANDFALL 
COORDINATES, THOUGH BROADER SYNOPTIC TRENDS REMAIN CONSISTENT. 
INTENSITY GUIDANCE IS SIMILARLY ALIGNED, DEPICTS MODEST 
INTENSIFICATION OR STEADY-STATE INTENSITY THROUGH LANDFALL FOLLOWED 
BY PRECIPITOUS WEAKENING. THE EXPECTED UPWARD ADJUSTMENT IN INITIAL 
INTENSITY WILL YIELD A HIGHER LANDFALL INTENSITY AND MAY EXTEND THE 
FORECAST DURATION AS THE SYSTEM ATTENUATES MORE SLOWLY THAN CURRENTLY 
ESTIMATED.

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