Advisories

WDPN31 PGTW 130900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT) 
WARNING NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.8N 146.3E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 218 NM NORTH OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) EXHIBITING MODERATE 
CONVECTIVE FLARING ALONG THE SOUTHEASTERN CONVERGENT ASYMPTOTE OVER 
THE PAST TWO HOURS. A 130300Z AMSR3 COLOR-ENHANCED 89GHZ MICROWAVE 
PASS REVEALED THE SHALLOW, NATURE OF THE WELL-DEFINED LOW-LEVEL 
BANDING FEATURES WRAPPING INTO THE CENTER, WITH ISOLATED CONVECTIVE 
CORES RESTRICTED ENTIRELY TO THE SOUTHEASTERN QUADRANT. ANIMATED 
WATER VAPOR IMAGERY AND ATMOSPHERIC MOTION VECTOR (AMV) ANALYSIS 
DEPICT A WEAK UPPER-LEVEL LOW (ULL) POSITIONED JUST SOUTHEAST
OF TD 28W, WITH AN ASSOCIATED INVERTED UPPER-LEVEL TROUGH EXTENDING
NORTH-NORTHEASTWARD DIRECTLY ACROSS THE VORTEX CORE. THIS UPPER-LEVEL
ENVIRONMENT EXERTS COMPETING INFLUENCES: IT SUPPORTS THE LOW-LEVEL 
CORE VIA MINIMAL VERTICAL WIND SHEAR (5-10 KTS), BUT SIMULTANEOUSLY
RESTRICTS UPPER-LEVEL POLEWARD OUTFLOW AND INTRODUCES DRY, SUBSIDENT
AIR INTO THE SYSTEM. THE INITIAL POSITION IS ASSESSED WITH HIGH 
CONFIDENCE BASED ON THE EXPOSED LLCC RESOLVED IN MSI. THE INITIAL 
INTENSITY IS ASSESSED WITH HIGH CONFIDENCE, ALIGNED WITH SUBJECTIVE 
AND OBJECTIVE SATELLITE ESTIMATES AND SUPPORTED BY RECENT 
SCATTEROMETER SIGNATURES INDICATING A COMPACT 25-KNOT SURFACE WIND 
FIELD IN THE NORTHEASTERN QUADRANT. ENVIRONMENTAL CONDITIONS ARE 
UNFAVORABLE FOR DEVELOPMENT, CONSTRAINED BY THE CLOSE PROXIMITY OF 
THE ULL AND ASSOCIATED TROUGH, HIGHLY RESTRICTED OUTFLOW ALOFT, AND 
AN INTRUSION OF DRY MID-LEVEL AIR DIRECTLY OVER THE LOW-LEVEL VORTEX.

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

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   CIMSS SATCON: 38 KTS AT 130610Z
   CIMSS ADT: 25 KTS AT 130540Z
   CIMSS AIDT: 32 KTS AT 130540Z
   CIMSS D-MINT: 24 KTS AT 130404Z
   CIMSS D-PRINT: 24 KTS AT 130640Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK WESTWARD
   OTHER FACTORS: DRY MID-LEVEL AIR OVERTOP OF THE LOW LEVEL CENTER
(LLC). 

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 (TWENTYEIGHT) IS
FORECAST TO TRACK NORTHWESTWARD, STEERED BY THE LOWER-LEVEL FLOW
ALONG THE SOUTHWESTERN FLANK OF A DEEP-LAYER SUBTROPICAL RIDGE (STR), 
THROUGHOUT THE FORECAST PERIOD. REGARDING INTENSITY, AS THE SYSTEM 
TRACKS NORTHWESTWARD, IT IS EXPECTED TO REMAIN SYNOPTICALLY COUPLED 
WITH THE ULL AND INVERTED TROUGH, RESULTING IN A PERSISTENT DEFICIT 
OF DIVERGENT OUTFLOW ALOFT DESPITE A LOW-SHEAR ENVIRONMENT. OVERALL, 
THE MID-LEVELS TO THE NORTH AND WEST ARE PROJECTED TO REMAIN DRY, 
ALTHOUGH SOME MESOSCALE MODELS INDICATE A MODEST IMPROVEMENT IN THE 
MOISTURE PROFILE NEAR TAU 24. TRANSIENT CONVECTIVE BURSTS WILL 
CONTINUE TO FLARE TEMPORARILY WITHIN THE CONVERGENT SOUTHEASTERN 
QUADRANT OVER THE NEXT 24 HOURS; HOWEVER, SUCH ACTIVITY WILL REMAIN 
UNABLE TO PERSIST OR ORGANIZE INTO CONVECTIVE CORES DUE TO THE 
INTRUSION OF THE DRY MID-LEVEL AIR AND THE DEFICIT OF A STABLE 
OUTFLOW MECHANISM ALOFT. THE LOWER-LEVEL VORTEX IS REASONABLY WELL 
DEFINED; CONSEQUENTLY, ITS DISSIPATION PROFILE WILL BE PROGRESSIVE, 
WITH DISSIPATION BELOW WARNING CRITERIA PROJECTED BY TAU 36.  

MODEL DISCUSSION: TRACK GUIDANCE IS IN EXCELLENT AGREEMENT, WITH
ALL CONSENSUS MEMBERS CONCURRING ON A NORTHWESTWARD TRAJECTORY 
THROUGH THE FORECAST PERIOD. THE GFS AND GEFS ENSEMBLE MEAN REPRESENT 
THE ONLY EXCURSIONS, DRIFTING SLIGHTLY POLEWARD OF THE PACK AND 
INCREASING CROSS-TRACK SPREAD TO 100 NM BY TAU 36. THE JTWC FORECAST 
FAVORS THE MULTI-MODEL CONSENSUS MEAN HIGH CONFIDENCE. INTENSITY 
GUIDANCE PRESENTS PRONOUNCED DISPERSION, PARTICULARLY AFTER TAU 
24. THE OPERATIONAL AND EXPERIMENTAL GOOGLE DEEPMIND ALONGSIDE THE
GFS DEPICT GRADUAL DECAY AND DISSIPATION BY TAU 36. CONVERSELY, 
THE HAFS-A, CTCX, AND STATISTICAL SHIPS-GFS SUITES DEPICT MODEST 
INTENSIFICATION FROM TAU 24 THROUGH TAU 120. THE SHIPS DEPICTS 
THE SYSTEM ATTAINING 50 KNOTS BY TAU 120; HOWEVER, THE DYNAMICAL 
FACTORS RESOLVED BY THE SHIPS SUITE DEPICT EXCESSIVE VWS (>30 KNOTS) 
AND A HOSTILE MOISTURE PROFILE (MID-LEVEL RH LESS THAN 40 PERCENT), 
RENDERING THIS RUN DYNAMICALLY INCONSISTENT. ACCORDINGLY, THE JTWC 
INTENSITY FORECAST LEANS TOWARD THE DEEPMIND AND GFS DECAY PROFILE 
WITH HIGH CONFIDENCE. 

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