Advisories

WDPN31 PGTW 150300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT) 
WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.3N 140.6E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 155 NM SOUTH-SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: WESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION (TD) 28W AS A FULLY EXPOSED, DIMINUATIVE SPINNER
COMPLETELY DEVOID OF CONVECTION AND OVERWHELMED BY DRY AIR. THE
142109Z HSCAT WINDSPEED DATA REVEALS MAXIMUM WINDS OF 20 KTS,
CAPTURED AS THE LIMITED CONVECTION COLLAPSED. ENVIRONMENTAL
ANALYSIS REVEALS A HIGHLY UNFAVORABLE ENVIRONMENT CHARACTERIZED BY
LOW TO MODERATE (15-20 KTS) VERTICAL WIND SHEAR (VWS), POOR
OUTFLOW, AND DRY SURROUNDING ENVIRONMENT, NEGLIGABLY OFFSET BY WARM
(28-29 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE FULLY EXPOSED LOW LEVEL
CIRCULATION CENTER (LLCC). THE INITIAL INTENSITY OF 25 KTS IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND
THE CIMSS AUTOMATED INTENSITY ESTIMATES, SUPPLEMENTED BY THE
PREVIOUSLY MENTIONED HSCAT WINDSPEED DATA.

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

CURRENT STEERING MECHANISM: LOW TO MID-LEVEL WESTERLY FLOW AROUND
THE DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   CIMSS ADT: 33 KTS AT 142340Z
   CIMSS AIDT: 33 KTS AT 142340Z
   CIMSS D-MINT: 23 KTS AT 142209Z
   CIMSS D-PRINT: 26 KTS AT 142340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR SURROUNDING THE SYSTEM

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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: TD 28W IS EXPECTED TO TRACK GENERALLY WESTWARD
FOR THE DURATION OF THE FORECAST WHILE IT REMAINS A SHALLOW SYSTEM
UNDER THE CONTROL OF THE LOW-LEVEL WESTERLY FLOW. THE ENVIRONMENT
IS EXPECTED TO REMAIN HOSTILE, WITH VWS REMAINING AROUND 15 KTS
THROUGH TAU 24, CONTRIBUTING TO FURTHER DRY AIR ENTRAINMENT. THE
DRY AIR WILL ULTIMATELY CAUSE 28W TO WEAKEN THROUGH TAU 24 UNTIL
DISSIPATION. HOWEVER, THERE IS A POSSIBILITY THAT THE SURFACE
CIRCULATION WILL OPEN INTO A TROUGH PRIOR TO TAU 24, AND THEREFORE
DISSIPATION EARLIER THAN EXPECTED.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN MODERATE
AGREEMENT THROUGH THE DURATION OF THE FORECAST PERIOD, THOUGH
SEVERAL MODELS DROP THE CIRCULATION PRIOR TO TAU 24. THE JTWC TRACK
FORECAST IS PLACED AMONG THE MAIN GROUPING OF MEMBERS -- INCLUDING
GFS, GEFS, AND THE EXPERIMENTAL AI MODELS -- WITH HIGH CONFIDENCE.
RELIABLE INTENSITY AIDS ARE IN STRONG AGREEMENT, SUPPORTING THE
JTWC INTENSITY FORECAST WITH HIGH CONFIDENCE. 

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