Advisories

WDPN31 PGTW 131500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT) 
WARNING NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.4N 145.4E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 253 NM NORTH 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 A FULLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC), WITH PERSISTENT
CONVECTION CONFINED ALONG THE SOUTHEASTERN CONVERGENT ASYMPTOTE. 
WHILE THIS DEEP CONVECTION HAS PERSISTED IN THE SOUTHEASTERN QUADRANT 
FOR BEYOND SIX HOURS, IT HAS BEEN SYSTEMATICALLY UNABLE TO WRAP INWARD 
TOWARD THE LLCC. TRANSIENT, ISOLATED CONVECTIVE BURSTS RESIDE WITHIN
THE WESTERN INFLOW BANDS, BUT LACK CONTINUITY AND DISSIPATE RAPIDLY.
A 131110Z ASCAT-C PASS RESOLVES AN ASYMMETRIC SURFACE WIND FIELD, 
CHARACTERIZED BY LIGHT, DISORGANIZED FLOW ACROSS THE WESTERN
SEMICIRCLE AND A 20-25 KNOT WIND BAND ALONG AN ARC EXTENDING FROM 
SOUTH OF THE LLCC UP THE EASTERN FLANK. THE INITIAL POSITION IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN EIR. THE
INITIAL INTENSITY IS ALSO ASSESSED WITH HIGH CONFIDENCE, BASED ON THE 
SCATTEROMETER SWATH AND ALIGNED WITH THE SUBJECTIVE AND OBJECTIVE 
INTENSITY ESTIMATES OUTLINED BELOW. ENVIRONMENTAL CONDITIONS ARE 
UNFAVORABLE FOR TROPICAL DEVELOPMENT. ALTHOUGH DEEP-LAYER SHEAR IS 
MINIMAL (0-5 KTS), TD 28W RESIDES DIRECTLY BENEATH A WEAK UPPER-LEVEL 
LOW (ULL) AND INVERTED UPPER-LEVEL TROUGH, HEAVILY RESTRICTING UPPER-
LEVEL OUTFLOW AND INTRODUCING DRY, SUBSIDENT AIR DIRECTLY OVER THE 
VORTEX CORE. THE 131200Z GUAM SOUNDING (THE NEAREST EMPIRICAL 
RAWINSONDE STATION) CONFIRMS A STRONG SUBSIDENCE INVERSION CAP AT 
730MB, WITH DEEP DRY AIR EXTENDING TO 300MB. NUMERICAL FIELDS SUPPORT 
A SYNOPTIC PROFILE OVER THE CORE OF 28W THAT IS ROUGHLY ANALOGOUS.

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

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED FAR TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   CIMSS SATCON: 42 KTS AT 130910Z
   CIMSS ADT: 25 KTS AT 131140Z
   CIMSS AIDT: 25 KTS AT 131140Z
   CIMSS D-MINT: 27 KTS AT 131201Z
   CIMSS D-PRINT: 27 KTS AT 131140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 0-5 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK WESTWARD
   OTHER FACTORS: HIGHLY CONSTRAINED UPPER-LEVEL OUTFLOW 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: TROPICAL DEPRESSION (TD) 28W IS FORECAST TO
CONTINUE TRACKING NORTHWESTWARD AT APPROXIMATELY 10 KNOTS ALONG THE
SOUTHWESTERN PERIPHERY OF THE EXPANSIVE STR THROUGHOUT THE FORECAST
PERIOD. REGARDING INTENSITY, 28W REMAINS IN CLOSE PROXIMITY TO THE
UPSTREAM ULL AND INVERTED TROUGH. OVER THE FORECAST TIMELINE, WHILE 
THE ULL IS PROJECTED TO DRIFT SOUTHWESTWARD, THE ASSOCIATED TROUGH 
AXIS WILL REMAIN COUPLED WITH THE LLCC. THE RESULTANT UPPER-LEVEL 
SUBSIDENCE, PERSISTENT DRY AIR ENTRAINMENT, AND THE LACK OF A ROBUST 
OUTFLOW MECHANISM WILL SUPPRESS INTENSIFICATION. MESOSCALE MODELS 
CONTINUE TO RESOLVE A BRIEF WINDOW OF MODEST MOISTURE IMPROVEMENT 
NEAR TAU 24, WHICH DRIVES AN INCORRECT MODEL PROJECTED RE-
INTENSIFICATION (DISCUSSED BELOW). HOWEVER, WHILE TRANSIENT 
CONVECTIVE CELLS MAY TEMPORARILY DEVELOP, PERSISTENCE IS UNLIKELY DUE 
TO THE ABSENCE OF AN ESTABLISHED UPPER-LEVEL EXHAUST MECHANISM. 
ACCORDINGLY, 28W WILL GRADUALLY WEAKEN AND DECAY, WITH DISSIPATION 
BELOW WARNING CRITERIA PROJECTED BY TAU 36. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN STRONG AGREEMENT, WITH
APPROXIMATELY 100NM OF CROSS-TRACK SPREAD BY TAU 36. THE JTWC
FORECAST IS POSITIONED NEAR THE AI-CONSENSUS MEAN WITH HIGH
CONFIDENCE. INTENSITY GUIDANCE CONTINUES TO EXHIBIT A BIFURCATION
IN THE TREND, WITH TAU 24 BEING THE INFLECTION POINT. THE GFS,
COTC, AND DEEPMIND (BOTH OPERATIONAL AND EXPERIMENTAL VERSIONS)
DEPICT THE SYSTEM MAINTAINING 25 KNOTS FOR ABOUT 12 TO 18 HOURS
BEFORE DISSIPATING BY TAU 36. THE HWRF, HAFS-A, CTCX AND
DECAY-SHIPS (GFS) MAINTAIN A 25-KNOT INTENSITY TO TAU 24, THEN 
UNREALISTICALLY INTENSIFY THE SYSTEM TO TO 30-35 KNOTS BY TAU 60
BEFORE WEAKENING TO DISSIPATION BY TAU 120. THE SHIPS CONTINUES
INTENSIFYING THROUGH TAU 120, UP TO 45 KNOTS. LIKELY THIS IS A
RESULT OF A KNOWN CONVECTIVE FEEDBACK BIAS IN THE GFS AND GFS-BASED
MODELS, WHICH IS UNREALISTICALLY DRIVING UP THE INTENSITY IN THE
MEDIUM- TO EXTENDED-RANGE FORECAST. THE JTWC FORECAST IS CONSISTENT
WITH THE DEEPMIND SOLUTION AND THE PREVIOUS FORECAST.  

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