Advisories

WDPN31 PGTW 130300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W (NANGKA) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.5N 148.2E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 323 NM EAST OF CHICHI JIMA
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 24 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION (TD) 16W (NANGKA) AS A QUICK MOVING SYSTEM WHOSE LOW
LEVEL CIRCULATION CENTER (LLCC) REMAINS OBSCURED BY A PERSISTENT
CENTRAL DENSE OVERCAST (CDO). DEFINITION OF LOW LEVEL CLOUD BANDS
AND THE CDO HAVE IMPROVED IN APPEARANCE OVER THE PAST SIX HOURS.
ENVIRONMENTAL ANALYSIS REVEALS MODERATE TO HIGH (20-25 KTS)
VERTICAL WIND SHEAR (VWS), OFFSET BY WARM (27-28 C) SEA SURFACE
TEMPERATURES (SSTS) AND STRONG POLEWARD OUTFLOW ALOFT. A 122256Z
METOP-B ASCAT IMAGE DEPICTS THE LLCC OF 16W EMBEDDED WITHIN A
LARGER TROUGH TO THE NORTHEAST, WITH THE HIGHEST WIND SPEEDS
LOCATED ON THE EASTERN SEMICIRCLE OF TD 16W. THE INITIAL POSITION
IS PLACED WITH HIGH CONFIDENCE BASED ON THE ASCAT DATA. THE INITIAL
INTENSITY IS ALSO ASSESSED WITH HIGH CONFIDENCE BASED OFF OF THE
ASCAT DATA, AGENCY DVORAK FIXES, AND CIMSS OBJECTIVE ESTIMATES
LISTED BELOW.

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

CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE (NER) CENTERED TO
THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T1.5 - 25 KTS
   CIMSS SATCON: 36 KTS AT 122300Z
   CIMSS ADT: 32 KTS AT 122300Z
   CIMSS AIDT: 35 KTS AT 122300Z
   CIMSS D-MINT: 29 KTS AT 122152Z
   CIMSS D-PRINT: 29 KTS AT 122330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MARGINAL 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 16W IS FORECAST TO CONTINUE TRACKING
NORTHEASTWARD AND MAKE AN EASTWARD TURN AFTER TAU 12. THE PRIMARY
STEERING INFLUENCE IS ASSESSED TO BE THE NEAR-EQUATORIAL RIDGE
(NER) CENTERED TO THE SOUTHEAST, VICE THE LOW-LEVEL MONSOONAL FLOW
DUE TO THE HIGH TRACK SPEED OF THE SYSTEM. COMPETING STEERING 
ENVIRONMENTS CONTINUE TO CREATE A BIFURCATION IN MODEL GUIDANCE BY 
TAU 24, WITH ONE SCENARIO DEPICTING A SLOWER TRACK SPEED OF 16W 
ALLOWING FOR THE NER AND SUBTROPICAL RIDGE (STR) TO THE NORTH TO 
BUILD INTO A NORTH-SOUTH ORIENTED RIDGING COMPLEX, DRIVING TD 16W 
POLEWARD. THE ALTERNATE SCENARIO, WHICH IS THE ONE REFLECTED IN THE 
OFFICIAL JTWC FORECAST, PREDICTS TD 16W TO MAINTAIN ITS CURRENT TRACK 
SPEED, REMAINING UNDER THE STEERING INFLUENCE OF THE NER AND TRACKING 
EASTWARD BEFORE IT BUILDS WITH THE STR TO THE NORTH. THERE IS STILL 
UNCERTAINTY IN THIS FORECAST TRACK, WITH THE TRACK SPEED OF 16W 
DIRECTLY IMPACTING WHAT STEERING ENVIRONMENT IT WILL BE IN BY TAUS 12 
TO 24. REGARDING INTENSITY, TD 16W IS EXPECTED TO MAINTAIN INTENSITY 
OUT TO TAU 24 AT WHICH POINT IT WILL ENCOUNTER AN INCREASED HOSTILE 
ENVIRONMENT OF DRY AIR ENTRAINMENT AND INCREASED VWS OF OVER 30 KTS, 
ULTIMATELY DISSIPATING BY TAU 48.

MODEL DISCUSSION: TRACK MODEL GUIDANCE CONTINUES TO BE IN POOR
AGREEMENT AND DISPLAY A BIFURCATION SCENARIO, WITH PHYSICS-BASED
MODELS PREDICTING A SLOWER TRACK SPEED AND SUBSEQUENT POLEWARD TURN
BY TAU 24. CONVERSELY, ALL AI-BASED MODELS DEPICT A FASTER TRACK
SPEED, RESULTING IN TD 16W TURNING EASTWARD BY TAU 24 AND PROGRESSING 
ACROSS THE NER PRIOR TO IT CONNECTING WITH THE STR TO THE NORTH. 
NAVGEM AND GOOGLE DEEPMIND ACCOUNT FOR THE WESTERN AND EASTERN MOST 
TRACKS, RESPECTIVELY, WITH THE ONLY NOTABLE CHANGE FROM THE PREVIOUS 
GUIDANCE PACKAGE BEING THE ECMWF ENSEMBLE MEAN DEPICTING THE POLEWARD 
TURN LATER THAN THE REMAINDER OF PHYSICS-BASED MODELS, MAKING IT 
CLOSER IN LINE WITH THE AI MODELS FOR THE FORECAST PERIOD. THE 
OFFICIAL JTWC FORECAST TRACK IS PLACED WITH LOW CONFIDENCE DUE TO THE 
CONTINUED SPREAD OF GUIDANCE, CLOSELY IN LINE WITH THE AI CONSENSUS 
AND EXPERIMENTAL GOOGLE DEEPMIND. MODEL INTENSITY GUIDANCE IS IN GOOD 
AGREEMENT WITH ALL MODELS DEPICTING A GRADUAL WEAKENING TREND OVER THE 
REMAINDER OF THE FORECAST PERIOD. THE OFFICIAL JTWC INTENSITY FORECAST 
IS ASSESSED WITH MEDIUM CONFIDENCE, IN LINE WITH THE MULTI-MODEL 
CONSENSUS OUT TO TAU 24 BEFORE DEVIATING TO DISSIPATE BY TAU 48, WHILE 
THE REMAINDER OF GUIDANCE CONTINUES TO PICK UP ON THE FLOW FROM THE 
BROADER TROUGHING.

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