Advisories

WDPN31 PGTW 140300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W (NANGKA) WARNING 
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.5N 153.4E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 260 NM NORTH OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION (TD) 16W (NANGKA) WITH A FULLY DECOUPLED AND EXPOSED LOW
LEVEL CIRCULATION CENTER (LLCC) WHICH HAS BEEN BECOMING INCREASINGLY 
ELONGATED OVER THE PAST SIX HOURS. A 132234Z METOP-B ASCAT PASS 
FURTHER VERIFIES THE ELONGATING LLCC AND DEPICTS A SWATH OF 30 KTS 
CONFINED TO THE NORTHERN SEMICIRCLE. ENVIRONMENTAL ANALYSIS REVEALS 
MARGINAL CONDITIONS WITH WARM (27-28 C) SEA SURFACE TEMPERATURES 
(SSTS) BEING OFFSET BY WEAK OUTFLOW ALOFT, HIGH (25-30 KTS) VERTICAL 
WIND SHEAR (VWS) AND DRY AIR ENTRAINMENT. THE INITIAL POSITION IS 
ASSESSED WITH HIGH CONFIDENCE BASED ON THE ASCAT DATA AND 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: EASTERN EXTENSION OF A NEAR-EQUATORIAL
RIDGE (NER) CENTERED TO THE SOUTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   CIMSS ADT: 34 KTS AT 132330Z
   CIMSS AIDT: 35 KTS AT 132330Z
   CIMSS D-MINT: 37 KTS AT 131951Z
   CIMSS D-PRINT: 28 KTS AT 132210Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK EASTWARD
   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 16W IS EXPECTED TO CONTINUE EASTWARD AT A
SLOWER TRACK SPEED FOR THE REMAINDER OF THE FORECAST PERIOD UNDER
THE SHALLOW STEERING INFLUENCE OF AN EASTWARD EXTENSION OF A NEAR-
EQUATORIAL RIDGE (NER) CENTERED TO THE SOUTHWEST. THIS EXTENSION
IS EXPECTED TO CONNECT WITH A SUBTROPICAL RIDGE (STR) CENTERED FAR
TO THE NORTHEAST BY TAU 24, FORMING A RIDGING COMPLEX SPANNING FROM
THE PHILIPPINE SEA TO THE INTERNATIONAL DATE LINE. THE SCENARIO
DEPICTED IN THE OFFICIAL JTWC FORECAST PREDICTS THIS RIDGING COMPLEX 
TO CAUSE AN EASTWARD STEERING INFLUENCE. CONVERSELY, THE ALTERNATE 
SCENARIO DEPICTED BY THE BIFURCATION OF MODEL GUIDANCE EXPECTS THE 
ELONGATED RIDGING COMPLEX TO CAUSE A POLEWARD TURN BY TAU 12, 
CONTRIBUTING TO CONTINUED UNCERTAINTY WITHIN THE FORECAST TRACK. 
REGARDING INTENSITY, TD 16W IS EXPECTED TO STEADILY DECREASE 
THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD AS IT WILL ENCOUNTER 
AN INCREASINGLY HOSTILE ENVIRONMENT OF CONTINUED DRY AIR ENTRAINMENT 
AND HIGH VERTICAL WIND SHEAR BROUGHT ON BY STRONG UPPER LEVEL 
WESTERLIES. THESE CONDITIONS WILL CONTINUE TO ELONGATE AND WEAKEN THE 
SYSTEM, WITH TD 16W ULTIMATELY FORECAST TO DISSIPATE BY TAU 36.

MODEL DISCUSSION: THE BIFURCATION IN TRACK MODEL GUIDANCE HAS SPREAD 
EVEN MORE, WITH A NEARLY 180 DEGREE SPLIT IN TRACK DIRECTION BY TAU 12 
BETWEEN THE OUTLIERS OF NAVGEM TO THE WEST AND ECMWF ENSEMBLE MEAN TO 
THE EAST. NOTABLY, MORE PHYSICS-BASED MODELS HAVE SHIFTED TO DEPICT 
THE EASTWARD TRACK IN BETTER AGREEMENT WITH THE AI-BASED MODELS. THE 
REMAINING MODELS THAT CONTINUE TO PREDICT A POLEWARD TURN ARE NAVGEM, 
UKMET ENSEMBLE MEAN, GFS, AND GEFS. JGSM, ECMWF, AND EC ENSEMBLE MEAN 
ALL NOW DEPICT AN EASTWARD TRACK, LENDING FURTHER CONFIDENCE TO THE 
FORECAST. THE OFFICIAL JTWC FORECAST TRACK IS PLACED WITH MEDIUM 
CONFIDENCE, CLOSELY IN LINE WITH THE BULK OF AI MODELS AND ALL 
PHYSICS-BASED MODELS MENTIONED ABOVE DEPICTING THE EASTWARD TRACK. 
MODEL INTENSITY GUIDANCE IS IN FAIR AGREEMENT WITH GOOGLE DEEPMIND AND 
HAFS-A DEPICTING A WEAKENING TREND AND DISSIPATING BY TAU 36 WHILE THE 
MULTI-MODEL CONSENSUS MAINTAINS TD 16W OUT TO TAU 120. THE OFFICIAL 
JTWC INTENSITY FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE, IN LINE 
WITH GOOGLE DEEPMIND AND HAFS-A TO DISSIPATE BY TAU 36 DUE TO THE
WORSENING ENVIRONMENTAL CONDITIONS.

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