Advisories

WDPN31 PGTW 132100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT) 
WARNING NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.1N 144.5E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 303 NM NORTH-NORTHWEST OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION (TD) 28W WITH A FULLY EXPOSED LOW LEVEL CIRCULATION
CENTER (LLCC) AND SMALL ISOLATED PUFFS OF CONVECTION ALONG THE
PERIPHERAL CLOUD LINES THAT QUICKLY DISSIPATE. ENVIRONMENTAL
CONDITIONS ARE ASSESSED AS UNFAVORABLE, DESPITE THE OTHERWISE
CONDUCIVE (28-29 C) SEA SURFACE TEMPERATURES (SSTS) AND LOW (5-10
KTS) VERTICAL WIND SHEAR (VWS). THESE CONDUCTIVE FACTORS ARE BEING 
OFFSET BY THE UPPER-LEVEL TROUGH WHICH 28W IS CURRENTLY SITUATED 
UNDERNEATH, WHICH IS SUBSIDING MID-LEVEL DRY AIR AND SUPPRESSING 
OUTFLOW ALOFT. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE 
BASED ON THE EXPOSED LLCC IN EIR. THE INITIAL INTENSITY IS ASSESSED 
WITH HIGH CONFIDENCE BASED ON EXCELLENT AGREEMENT ACROSS THE PGTW FIX 
AND 
CIMSS OBJECTIVE ESTIMATES LISTED BELOW.

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

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A SUBTROPICAL
RIDGE CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   CIMSS ADT: 25 KTS AT 131740Z
   CIMSS AIDT: 30 KTS AT 131740Z
   CIMSS D-MINT: 25 KTS AT 131551Z
   CIMSS D-PRINT: 26 KTS AT 131740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK EQUATORWARD
   OTHER FACTORS: UPPER-LEVEL TROUGH SUPPRESSING OUTFLOW ALOFT AND
DRY MID-LEVEL AIR

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 CONTINUE TO TRACK
NORTHWESTWARD FOR THE REMAINDER OF THE FORECAST PERIOD, STEERED BY
THE LOW LEVEL FLOW FROM THE WESTERN PERIPHERY OF THE SUBTROPICAL
RIDGE (STR) CENTERED TO THE NORTHEAST. REGARDING INTENSITY, 28W IS
EXPECTED TO REMAIN AT 25 KTS FOR THE NEXT 18 TO 24 HOURS BEFORE
DISSIPATING OVER WATER NO LATER THAN TAU 36 AS IT OPENS UP INTO A
TROUGH. THE UPPER-LEVEL TROUGH IS EXPECTED TO PROPAGATE WESTWARD
AND REMAIN OVER 28W FOR THE DURATION OF THE FORECAST PERIOD,
PREVENTING ANY FURTHER DEVELOPMENT AS IT CONTINUES TO SUPPRESS
OUTFLOW ALOFT AND INTRODUCE FURTHER DRY AIR. IT IS POSSIBLE THAT
ADDITIONAL SMALL, ISOLATED PUFFS OF CONVECTION CONTINUE TO FORM ON
THE PERIPHERY OF THE SYSTEM AS HAS BEEN THE CASE FOR THE LAST FEW
CYCLES, BUT THESE ARE ASSESSED TO BE UNLIKELY TO CONSOLIDATE OR
LEAD TO ANY FURTHER DEVELOPMENT.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN EXCELLENT AGREEMENT
OUT TO TAU 36 WITH A 50 NM CROSS-TRACK SPREAD AND 45 NM ALONG TRACK
SPREAD. THE OFFICIAL JTWC FORECAST TRACK IS LAID WITH HIGH
CONFIDENCE, IN LINE WITH THE MULTI-MODEL CONSENSUS. MODEL INTENSITY
GUIDANCE CONTINUES TO SHOW A SPLIT, WITH THE GFS AND GOOGLE
DEEPMIND INDICATING IMMINENT WEAKENING AND DISSIPATION, WHEREAS THE
MESOSCALE MODELS OF HAFS-A, COAMPS-TC (GFS BASED), HWRF, AND BOTH
DECAY SHIPS MODELS DEPICT A STEADY INTENSITY OF 25-30 KTS FOR THE
FIRST 24 HOURS FOLLOWED BY MODERATE INTENSIFICATION THEREAFTER.
WHILE THIS INCREASES THE UNCERTAINTY, THERE IS LESS CONFIDENCE IN THE
LATTER SCENARIO BASED ON A KNOWN BIAS IN THESE GFS-BASED MODELS TO
OVER-INTENSIFY ANY CONVECTIVE SIGNATURES. THE OFFICIAL JTWC FORECAST 
INTENSITY IS THUS ASSESSED WITH MEDIUM CONFIDENCE IN LINE WITH THE GFS 
AND GOOGLE DEEPMIND AS THE AFOREMENTIONED DETRIMENTAL MID AND UPPER-
LEVEL CONDITIONS WILL RESTRICT FURTHER INTENSIFICATION.

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