Advisories

WDPN31 PGTW 130300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT) 
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.0N 147.3E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 189 NM NORTH-NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION (TD) 28W AS A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER
(LLCC) DEVOID OF ANY STRONG CONVECTION. A 122338Z METOP-B ASCAT
PASS REVEALS AN ASYMMETRICAL WIND FIELD WITH THE MAJORITY OF
ENHANCED WIND SPEEDS CONFINED TO THE NORTHEAST AND A MAXIMUM WIND
SPEED OF 25 KTS. ENVIRONMENTAL CONDITIONS ARE ASSESSED AS MARGINAL,
AS WARM (28-29 C) SEA SURFACE TEMPERATURES (SSTS) AND LOW (5-10
KTS) VERTICAL WIND SHEAR (VWS) ARE OFFSET BY DRY AIR ENTRAINMENT
AND SUPPRESSED OUTFLOW ALOFT DUE TO A TROPICAL UPPER TROPOSPHERIC
TROUGH (TUTT) SITUATED DIRECTLY ABOVE 28W. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN MSI. THE
INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
ASCAT DATA.

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
   RJTD: T1.0 - 25 KTS
   CIMSS SATCON: 40 KTS AT 122119Z
   CIMSS ADT: 34 KTS AT 122330Z
   CIMSS AIDT: 30 KTS AT 122330Z
   CIMSS D-MINT: 27 KTS AT 122316Z
   CIMSS D-PRINT: 24 KTS AT 132330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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 FORECAST TO TRACK NORTHWESTWARD FOR
THE REMAINDER OF THE FORECAST PERIOD UNDER THE STEERING INFLUENCE
OF THE LOW-LEVEL FLOW ASSOCIATED WITH THE SUBTROPICAL RIDGE (STR)
CENTERED TO THE NORTHEAST. REGARDING INTENSITY, 28W IS FORECAST TO
MAINTAIN INTENSITY FOR THE NEXT 12 TO 24 HOURS BEFORE WEAKENING AND
OPENING INTO A TROUGH NO LATER THAN TAU 36 AS CONTINUED DRY AIR
ENTRAINMENT AND SUPPRESSED OUTFLOW ALOFT WILL PREVENT FURTHER
INTENSIFICATION. THERE IS A POSSIBILITY FOR THE SYSTEM TO DISSIPATE
PRIOR TO TAU 36 DEPENDING ON HOW QUICKLY THESE CONTINUED
ENVIRONMENTAL CONDITIONS WILL DETERIORATE THE SYSTEM, BUT THAT IS
NOT REFLECTED IN THE OFFICIAL JTWC FORECAST.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT FOR THE
REMAINDER OF THE FORECAST PERIOD WITH A CROSS-TRACK SPREAD OF 85 NM
AND AN ALONG-TRACK SPREAD OF 35 NM AT TAU 36. THE OFFICIAL JTWC
TRACK FORECAST IS THUS LAID WITH HIGH CONFIDENCE, CLOSELY IN LINE
WITH THE MULTI-MODEL CONSENSUS. TRACK INTENSITY GUIDANCE IS IN LESS
AGREEMENT, WITH AN OUTLIER OF GFS-BASED COAMPS-TC DEPICTING A BRIEF
INTENSIFICATION PEAKING AT TAU 24 AND WEAKENING THEREAFTER, WHILE
SOME OTHER GUIDANCE DEPICT DISSIPATION PRIOR TO TAU 36. THE
OFFICIAL JTWC INTENSITY FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE
DUE TO THE UNCERTAINTY REGARDING POTENTIAL DISSIPATION PRIOR TO TAU
36.

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