Advisories

WDXS31 PGTW 200900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 02S (TWO) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 4.5S 53.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 877 NM EAST OF DAR ES SALAAM, TANZANIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT
CIRCULATION WITH THE LOW-LEVEL CIRCULATION CENTER (LLCC) PARTIALLY
OBSCURED BY A RAGGED CENTRAL DENSE OVERCAST (CDO). CURVED BANDING
EXTENDS WESTWARD AND SOUTHWARD FROM THE CENTER. A 200545Z ASCAT-B
IMAGE REVEALED A WELL-DEFINED LLCC WITH GALE-FORCE WINDS IN THE
SOUTHWEST QUADRANT. THE ENVIRONMENT IS GENERALLY FAVORABLE,
CHARACTERIZED BY LOW TO MODERATE NORTHEASTERLY VERTICAL WIND SHEAR
(VWS), MODERATE WESTWARD UPPER-LEVEL DIVERGENCE, AND WARM SEA
SURFACE TEMPERATURES (SST). THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE NEAR THE PGTW FIX. THE INITIAL INTENSITY IS SET
AT 35 KTS WITH HIGH CONFIDENCE BASED ON T2.5 DVORAK ESTIMATES FROM
PGTW AND FMEE, AS WELL AS SCATTEROMETER DATA.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
(STR) CENTERED OVER NORTHERN MADAGASCAR

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

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE 02S IS MOVING
WEST-SOUTHWESTWARD ALONG THE NORTHERN PERIPHERY OF A STR TO THE
SOUTH. OVER THE NEXT 24 HOURS, A NEAR-EQUATORIAL RIDGE WILL BUILD
TO THE WEST OF THE SYSTEM, LEADING TO A TURN TOWARD THE SOUTHWEST.
AFTER TAU 36, THE STR TO THE SOUTH WILL BUILD, TURNING THE SYSTEM
BACK TOWARD THE WEST. LOW TO MODERATE VWS WILL PERSIST, WHILE SST
WILL GRADUALLY DECREASE TO 27 DEGREES CELSIUS BY TAU 48. THESE
GENERALLY FAVORABLE CONDITIONS WILL SUPPORT STEADY INTENSIFICATION
THROUGH TAU 36. AFTER TAU 48, VWS WILL INCREASE TO 25 KTS AND SHIFT
TO A MORE NORTHWESTERLY DIRECTION, ENTRAINING COPIOUS AMOUNTS OF
DRY AIR INTO THE CIRCULATION. THESE MORE HOSTILE CONDITIONS WILL
RESULT IN GRADUAL WEAKENING, WITH DISSIPATION PREDICTED BY TAU 96.

MODEL DISCUSSION: TRACK GUIDANCE IS QUITE SPREAD OUT, WITH AI
MODELS INDICATING A LESS POLEWARD TRACK THAN THE DYNAMICAL MODELS.
HAFS-A AND GFS ARE WELL TO THE SOUTH OF THE AI-MODEL MEAN, WHILE
THE GOOGLE DEEPMIND GUIDANCE LIES FARTHER NORTH. ECMWF IS MORE
ALIGNED WITH THE AI GUIDANCE. THE JTWC FORECAST TRACK IS PLACED
VERY NEAR THE AI-MODEL MEAN, INDICATING A LESS POLEWARD TRACK THAN
THE BULK OF THE PHYSICS-BASED MODELS. SIMILARLY, SIGNIFICANT SPREAD
EXISTS AMONG THE INTENSITY AIDS. HAFS-A AND GFS ARE THE WEAKEST
SOLUTIONS, WHILE DEEPMIND DEPICTS A PEAK INTENSITY OF 65 KTS. GIVEN
THE PERSISTENT SHEAR, THE JTWC INTENSITY FORECAST IS SET NEAR THE
CENTER OF THE GUIDANCE ENVELOPE, INDICATING ONLY MODEST
INTENSIFICATION. HOWEVER, IF THE SHEAR EASES, THE COMPACT SYSTEM
MAY INTENSIFY MORE QUICKLY AND ACHIEVE A HIGHER PEAK INTENSITY THAN
FORECAST.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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