Advisories

WDPN31 PGTW 122100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT) 
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.5N 148.2E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 195 NM NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS THE
PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) OF TROPICAL
DEPRESSION (TD) 28W WITH A SHEARED CENTRAL DENSE OVERCAST (CDO)
THAT HAS RAPIDLY DETERIORATED OVER THE PAST SIX HOURS, WITH CLOUD
TOPS WARMING FROM -75 C TO -60 C. ENVIRONMENTAL CONDITIONS REMAIN
MARGINAL WITH WARM (28-29 C) SEA SURFACE TEMPERATURES (SSTS) BEING
OFFSET BY 10-15 KTS OF NORTHERLY VERTICAL WIND SHEAR (VWS), WEAK
EQUATORWARD OUTFLOW ALOFT, AND A LARGE AREA OF DRY AIR DUE TO A
TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) SITUATED JUST TO THE EAST
OF 28W. THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE BASED ON
THE OBSCURED LLCC IN EIR. THE INITIAL INTENSITY IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE PGTW FIX AND AGREEMENT ACROSS
OBJECTIVE ESTIMATES, WITH THE HIGHER END OF CIMSS ESTIMATES HAVING
BEEN COMPUTED BEFORE THE BULK OF THE CONVECTION COLLAPSED.

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

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE
NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   CIMSS SATCON: 36 KTS AT 121610Z
   CIMSS ADT: 34 KTS AT 121740Z
   CIMSS AIDT: 31 KTS AT 121740Z
   CIMSS D-MINT: 29 KTS AT 121610Z
   CIMSS D-PRINT: 28 KTS AT 121710Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK EQUATORWARD
   OTHER FACTORS: EXTENSIVE DRY AIR

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 FORECAST TO TRACK STEADILY
NORTHWESTWARD FOR THE REMAINDER OF THE FORECAST PERIOD UNDER THE
STEERING INFLUENCE OF THE LOW-LEVEL SOUTHEASTERLY FLOW OF THE
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST. REGARDING
INTENSITY, 28W IS EXPECTED TO MAINTAIN ITS CURRENT INTENSITY IN THE
SHORT TERM BEFORE WEAKENING AND ULTIMATELY DISSIPATING OVER WATER
BY TAU 48 AS ENVIRONMENTAL CONDITIONS ARE NOT EXPECTED TO IMPROVE
TO ALLOW FURTHER CONSOLIDATION OR INTENSIFICATION. FURTHERMORE, BY
TAU 48 28W WILL ENCOUNTER A SHEAR LINE AND FURTHER DRY AIR, CAUSING
28W TO OPEN INTO A TROUGH.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT, WITH
GFS AND GEFS BEING THE QUICKEST AND MOST POLEWARD SOLUTIONS,
RESULTING IN AN OVERALL CROSS-TRACK SPREAD OF 100 NM AND AN
ALONG-TRACK SPREAD OF 75 NM BY TAU 48. THE OFFICIAL JTWC FORECAST
TRACK IS THUS PLACED WITH HIGH CONFIDENCE, IN LINE WITH THE
MULTI-MODEL CONSENSUS. INTENSITY GUIDANCE HAS COME INTO BETTER
AGREEMENT, WITH THE MAJORITY NOW DEPICTING A PLATEAU IN INTENSITY
OUT TO TAU 12 FOLLOWED BY WEAKENING THEREAFTER, WITH THE OUTLIERS
OF DECAY-SHIPS (BOTH GFS AND NAVGEM BASED), WHICH DEPICT FURTHER
INTENSIFICATION. THE OFFICIAL JTWC FORECAST INTENSITY IS ASSESSED
WITH HIGH CONFIDENCE, BELOW THE MULTI-MODEL CONSENSUS DUE TO THE
DISREGARDED SHIPS GUIDANCE, HEDGING TOWARDS THE GOOGLE DEEPMIND,
GFS, AND HAFS-A SOLUTIONS BASED ON THE AFOREMENTIONED UNFAVORABLE
ENVIRONMENTAL CONDITIONS.

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