Tropical Storm NANMADOL Advisory 9月14日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (NANMADOL) WARNING NR
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 22.5N 140.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 151 NM SOUTH-SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) AND CIRA PROXY VISIBLE SATELLITE
IMAGERY DEPICTS PARTIALLY EXPOSED LOW LEVEL BANDING WRAPPING INTO
AN IMPROVING LOW LEVEL CIRCULATION CENTER (LLCC), WITH A BROAD
PLUME OF FLARING DEEP CONVECTION TRAILING TO THE SOUTHWEST. IN THE
HOURS SINCE ANALYSIS TIME, CONVECTION HAS STEADILY BEEN BUILDING
OVER THE NORTHWEST QUADRANT, FURTHER EVIDENCE THAT TS NANMADOL IS
COMING TOGETHER. A 131837Z GMI 36GHZ IMAGE REVEALS FORMATIVE
BANDING STRUCTURES ALONG THE SOUTHERN SEMI-CIRCLE WRAPPING INTO AN
LOOSELY DEFINED CENTER, WITH FRAGMENTED BANDING STRUCTURE IN THE
SUBSIDENT DRY AIR TO THE NORTH AND WEST. NO RECENT SCATTEROMETRY
HAS BEEN AVAILABLE TO ASSIST IN LOCATING THE CENTER AND TO CONFIRM
THE CURRENT INTENSITY. DUE TO THE CDO OBSCURATION AND POORLY DEFINED
MICROWAVE CENTER, THE INITIAL POSITION IS PLACED BASED ON
MULTI-AGENCY FIX POSITIONS FROM PGTW, KNES, AND RJTD WITH LOW
CONFIDENCE. THE INITIAL INTENSITY WAS UPGRADED TO 35 KNOTS BASED ON
DVORAK ESTIMATES OF T2.5 FROM ALL AGENCIES. OBJECTIVE ADT AND
SATCON ARE 43 KNOTS. ENVIRONMENTAL FACTORS ARE INCREASINGLY
FAVORABLE FOR FURTHER DEVELOPMENT WITH LOW (10-15 KTS) 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. TS 16W
CONTINUES TO SLOWLY TRACK EAST-NORTHEASTWARD UNDER A WEAK STEERING
ENVIRONMENT, ALTHOUGH THE SLOWDOWN IN THE MOST RECENT FIXES
SUGGESTS THE EXPECTED TURN BACK TO THE NORTHWEST MAY COMMENCE SOON.
INITIAL WIND RADII BASIS: ASSESSED BASED ON STRONG CONVECTION IN
SOUTHEAST QUADRANT
CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTH
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 42 KTS AT 131614Z
   CIMSS ADT: 43 KTS AT 131740Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   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 RIDGE TO THE NORTH IS EXPECTED
TO BUILD, ALLOWING TS 16W TO MAKE A TURN TO WEST-NORTHWEST OVER THE
NEXT 12 TO 24 HOURS. THIS STR SHOULD REMAIN THE PRIMARY STEERING
MECHANISM OVER THE COURSE OF THE FORECAST, WITH GENERALLY
NORTHWESTWARD MOTION PERSISTING UNTIL AFTER TAU 72. AFTER THIS TIME,
THE SYSTEM SHOULD BEGIN TO ROUND THE RIDGE, TURNING MORE NORTHWARD AS
A RESULT. THE FORECAST INTENSITY TREND WAS UPDATED TO BE MORE
AGGRESSIVE IN THE SHORT TERM IN RESPONSE TO THE IMPROVING SATELLITE
DEPICTION, AND ACCOUNTING FOR A NUMBER OF RAPID INTENSIFICATION (RI)
AIDS THAT ARE NOW INDICATING A HIGH LIKELIHOOD OF RI. THE PEAK
INTENSITY WAS SET TO 100 KNOTS AT TAU 72, 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. IT SHOULD BE
NOTED THAT THE LATEST GUIDANCE FROM GFS AND ECMWF IN PARTICULAR
ARE SUGGESTING A TRACK FURTHER WESTWARD IN THE EXTENDED RANGE.
GFS IN PARTICULAR, MAY BE INTERACTING WITH A MID-LEVEL LOW THAT
FORMS OVER EASTERN CHINA. THE FORECAST TRACK WAS SHIFTED SLIGHTLY
TO THE SOUTH AND WEST, BUT STILL ASSUMING THE RECURVE PHILOSOPHY AS
PREVIOUSLY ESTABLISHED.
MODEL DISCUSSION: GFS AND ECMWF ARE THE PRIMARY GUIDANCE TAKING THE
MORE WESTWARD TRACK IN THEIR RESPECTIVE DETERMINISTIC SOLUTIONS.
THE ENSEMBLE GUIDANCE SUGGESTS AN APPROXIMATE 15 TO 20 PERCENT
PROBABILITY OF THIS SCENARIO. A STRONG TYPHOON, AS PREDICTED BY
RELIABLE GUIDANCE, SHOULD FAVOR THE EROSION OF THE STR, RESULTING
IN THE FORECAST RECURVATURE. 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 FORECAST TRACK.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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