Tropical Storm NANMADOL Advisory Mi, 14.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (NANMADOL) WARNING NR
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 22.7N 140.4E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 135 NM SOUTH-SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS CONTINUING
IMPROVEMENT OF LOW LEVEL BANDING WRAPPING INTO A DEEPENING LOW LEVEL
CIRCULATION CENTER (LLCC), WITH A BROADENING PLUME OF FLARING DEEP
CONVECTION CONSISTENT WITH A MONSOON DEPRESSION. A 132143Z SSMIS 91GHZ
IMAGE REVEALS A LARGE FEEDER BAND WRAPPING ALONG THE SOUTHERN
PERIPHERY INTO WHAT IS STILL AN ILL-DEFINED CENTER. NO RECENT
SCATTEROMETRY HAS BEEN AVAILABLE TO ASSIST IN LOCATING THE CENTER AND
TO CONFIRM THE CURRENT INTENSITY. THE INITIAL POSITION IS PLACED BASED
ON MULTI-AGENCY MSI-BASED FIX POSITIONS FROM PGTW, KNES, AND RJTD WITH
MEDIUM CONFIDENCE. THE INITIAL INTENSITY WAS UPGRADED TO 40 KNOTS
BASED ON DVORAK ESTIMATES OF T2.5 FROM ALL AGENCIES, AND ACCOUNTING
FOR THE OVERALL IMPROVEMENT IN THE SATELLITE DEPICTION, WITH THE
LATEST CIMSS SATCON VALUE COMING IN AT 41 KNOTS. ENVIRONMENTAL FACTORS
ARE INCREASINGLYFAVORABLE FOR FURTHER DEVELOPMENT WITH LOW (5-10
KNOTS) VERTICAL WIND SHEAR (VWS), AND WARM (29-30) SEA SURFACE
TEMPERATURES (SSTS). OUTFLOW IS STILL PRIMARILY CONSTRAINED TO
EQUATORWARD CHANNELS DUE TO POSITIONING OF THE SUBTROPICAL RIDGE TO
THE NORTH INHIBITING THE POLEWARD FLOW. CIMSS TPW PRODUCT INDICATES
CROSS-EQUATORIAL INFLOW IS PROVIDING AMPLE INFLUX OF DEEP TROPICAL
MOISTURE. BASED ON LIMITED AVAILABLE DATA, TS 16W CONTINUES TO SLOWLY
DRIFT EAST-NORTHEASTWARD UNDER A WEAK STEERING ENVIRONMENT.
INITIAL WIND RADII BASIS: AMSR2 WINDS
CURRENT STEERING MECHANISM: WEAK STEERING DUE TO COMPETING
MECHANISMS
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 44 KTS AT 132204Z
   CIMSS ADT: 39 KTS AT 132340Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: DEEP TROPICAL MOISTURE INFLOW
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: LOW
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: THE SUBTROPICAL STEERING RIDGE (STR) TO THE
NORTH IS EXPECTED TO BUILD, ALLOWING TS 16W TO FINALLY MAKE A TURN
TO WEST-NORTHWEST OVER THE NEXT 12 HOURS. THIS STR SHOULD REMAIN
THE PRIMARY STEERING MECHANISM OVER THE COURSE OF THE FORECAST,
WITH GENERALLY NORTHWESTWARD MOTION PERSISTING UNTIL TAU 72.
BETWEEN TAU 72 TO 96, A REORIENTATION OF THIS STR SHOULD DEFLECT
THE TRACK WITH A MORE NORTHERLY COMPONENT, TAKING NANMADOL VERY
CLOSE TO THE ISLANDS OF MINAMI DAITO JIMA AND AMAMI OSHIMA BEFORE
BEGINNING TO ROUND THE STR. THE PREVIOUS FORECAST CYCLE SAW SOME
ODD OUTLIER TRACKS IN THE CONSENSUS, RAISING THE POSSIBILITY OF A
MORE WESTWARD TRACK INTO THE EAST CHINA SEA. THE LATEST CYCLE HAS
THE AIDS COMING BACK INTO BETTER AGREEMENT WITH THE REST OF THE
PACKAGE, ALL INDICATING A RECURVE SCENARIO. AT TAU 96, THERE IS
ONLY 86 NM OF ACROSS TRACK SPREAD. ADDITIONALLY, THE NUMBER OF
ENSEMBLE MEMBERS WITH A WESTWARD EXTENDED TRACK ALSO WENT DOWN THIS
CYCLE. THE FORECAST INTENSITY TREND WAS MAINTAINED CLOSE TO THE
PRIOR CYCLE, REFLECTING CONTINUED SIGNS OF RAPID DEVELOPMENT IN THE
SHORT TERM. WHILE AGGRESSIVE, THE FORECAST INTENSITY TREND ALSO
CONSIDERED THE LARGE SIZE OF THIS SYSTEM, WHICH SHOULD LIMIT
POTENTIAL FOR EXPLOSIVE DEEPENING. THAT SAID, WITH AMPLE 29 TO 30
DEGREE C SSTS AND LOW VWS IN ITS PATH, THE PEAK FORECAST INTENSITY
OF 100 KNOTS AT TAU 72 IS BASED LARGELY ON MODEL GUIDANCE FROM GFS,
HWRF, AND COAMPS-TC ENSEMBLE. VERTICAL WIND SHEAR AND DECREASING
SST AT THE FINAL POSIT SHOULD RESULT IN A SLOW WEAKENING TREND AT
THE END OF THE FORECAST PERIOD.
MODEL DISCUSSION: AS NOTED, THE 18Z GFS CAME INTO BETTER AGREEMENT
WITH THE REST OF THE MULTI-MODEL CONSENSUS. LIKEWISE, THE 18Z ECMWF
TRACK (AVAILABLE THROUGH TAU 96) INDICATES THIS MODEL IS ALSO NOW
IN GENERAL AGREEMENT. BEYOND TAU 96, THE PICTURE IS STILL MURKY,
WITH DIFFERENCES IN THE TIMING AND POSITION OF RECURVATURE MORE
PRONOUNCED (SPREAD IS 218 NM). THE TRACK WAS PLACED CLOSE TO THE
PRIOR FORECAST AND SLIGHTLY WEST OF THE CONSENSUS MEAN, WEIGHTING
TOWARDS THE GFS AND EURO SOLUTIONS. WHILE THE FORECAST TAKES TS
NANMADOL TOWARDS THE KOREAN STRAIGHT, A SHARPER TURN TOWARDS KYUSHU
IS STILL A DISTINCT POSSIBILITY. THE TIMING AND LATITUDE OF
NANMADOLS TURN BACK TO THE WEST COULD AFFECT THE ULTIMATE LONG RANGE
POSITING. ONCE THE TURN IS MADE, THERE SHOULD BE BETTER CLARITY IN THE
MODELS. UNTIL THEN, THERE IS LOW CONFIDENCE IN THE EXTENDED
FORECAST TRACK.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
NNNN
NNNN