Advisories

WDPN31 PGTW 142100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGH) 
WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.7N 141.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 126 NM SOUTH OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION (TD) 28W AS AN ELONGATED SYSTEM WEAKLY CLOSED ALONG THE
SOUTHERN FLANK WITH COLLAPSING DEEP CONVECTION. THE PREVIOUS BURST
OF DEEP CONVECTION WAS SHORT LIVED, AND THE LOW-LEVEL CIRCULATION
CENTER MAY BECOME EXPOSED ONCE AGAIN. ENVIRONMENTAL ANALYSIS
REVEALS A MARGINAL ENVIRONMENT, CHARACTERIZED BY LOW (5-10 KTS)
VERTICAL WIND SHEAR (VWS) AND WARM (28-29 C) SEA SURFACE
TEMPERATURES (SST), OFFSET BY HIGH AMOUNTS OF MID-LEVEL DRY AIR
SURROUNDING THE SYSTEM AND LIMITED OUTFLOW ALOFT. THE INITIAL
POSITION IS PLACED WITH LOW CONFIDENCE BASED ON LOW-LEVEL CLOUD
BANDING OBSERVED AROUND AND THROUGH THE COLLAPSING DEEP CONVECTION.
THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGENCY DVORAK FIXES AND THE CIMSS AUTOMATED INTENSITY
ESTIMATES LISTED BELOW.

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 SATCON: 39 KTS AT 141710Z
   CIMSS ADT: 33 KTS AT 141740Z
   CIMSS AIDT: 34 KTS AT 141740Z
   CIMSS D-MINT: 33 KTS AT 141616Z
   CIMSS D-PRINT: 29 KTS AT 141740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: COMPACT SIZE OF THE SYSTEM; DRY MID-LEVEL AIR
SURROUNDING THE INNER CORE; RESTRICTED OUTFLOW ALOFT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   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 GET PROGRESSIVELY WORSE, WITH VWS INCREASING UPWARDS
OF 20 KTS BY TAU 36, CONTRIBUTING TO FURTHER DRY AIR ENTRAINMENT.
THE COMBINATION OF SHEAR AND DRY AIR WILL ULTIMATELY CAUSE 28W TO
WEAKEN THROUGH TAU 36 UNTIL DISSIPATION. HOWEVER, THERE IS A
POSSIBILITY THAT THE SURFACE CIRCULATION WILL OPEN INTO A TROUGH
PRIOR TO TAU 36, AND THEREFORE DISSIPATION EARLIER THAN EXPECTED.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN MODERATE
AGREEMENT THROUGH TAU 36. 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//
NNNN