Advisories

WDPN31 PGTW 120300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.4N 150.8E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 378 NM EAST-NORTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY-
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH LOW-LEVEL CLOUD LINES 
WRAPPING INTO A DEFINED, CLOSED CENTER AND FORMATIVE DEEP CONVECTIVE 
BANDING OVER THE SOUTHERN SEMICIRCLE. A RECENT SCATTEROMETER IMAGE 
INDICATES A CLOSED CIRCULATION WITH 25-30 KNOT WINDS OVER THE SOUTHERN 
QUADRANT AND 15-20 KNOTS ELSEWHERE. THE INITIAL INTENSITY IS ASSESSED 
AT 25 KNOTS BASED ON THE PGTW DVORAK ESTIMATE AND OVERALL WINDFIELD. 
THIS ASYMMETRY IS ALSO EVIDENT IN AN 112132Z SSMIS 37GHZ MICROWAVE 
IMAGE, WHICH SHOWS FORMATIVE CURVED BANDING OVER THE SOUTHERN QUADRANT 
BUT WEAK LOW-LEVEL STRUCTURE OVER THE NORTHERN QUADRANT. UPPER-LEVEL 
ANALYSIS INDICATES A MARGINAL ENVIRONMENT DUE TO THE AN ELONGATED TUTT 
CELL POSITIONED NEAR 15N 156E, WHICH IS PRODUCING VIGOROUS NORTHERLY 
FLOW OVER THE SYSTEM AND LOW TO MODERATE VERTICAL WIND SHEAR (VWS).

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

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
(STR) POSITIONED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: EXTENSIVE DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) IS FORECAST TO REMAIN
AT TD STRENGTH THROUGH THE ENTIRE FORECAST PERIOD DUE TO THE PRESENCE 
OF EXTENSIVE DRY AIR THROUGHOUT THE REGION AND MARGINAL UPPER-LEVEL 
FLOW ASSOCIATED WITH THE AFOREMENTIONED TUTT CELL AND BROAD CYCLONIC 
FLOW. THIS REGION OF CYCLONIC FLOW WILL PERSIST OVER THE SYSTEM 
THROUGH TAU 48 OR LONGER. THE SYSTEM WILL TRACK NORTHWESTWARD THROUGH 
TAU 48 ALONG THE SOUTHWESTERN PERIPHERY OF THE LOW- TO MID-LEVEL STR, 
AND WILL STRUGGLE TO CONSOLIDATE THEN DISSIPATE BY TAU 48 DUE TO THE 
PERSISTENT CONVERGENT, CYCLONIC FLOW AND EXTENSIVE DRY AIR.        

MODEL DISCUSSION: DUE TO THE ENTRENCHED SUBTROPICAL STEERING RIDGE,
PHYSICS-BASED AND AI-BASED MODEL GUIDANCE ARE IN GOOD AGREEMENT
WITH A 125NM CROSS-TRACK SPREAD AT TAU 48. THE JTWC TRACK FORECAST
IS BASED ON A BLEND OF AICN, CONW AND GDMI WITH MEDIUM CONFIDENCE.
RELIABLE INTENSITY GUIDANCE INDICATES A FLAT OR STEADILY WEAKENING
TREND THROUGH THE FORECAST PERIOD SUPPORTING THE JTWC INTENSITY
FORECAST WITH MEDIUM CONFIDENCE.    

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