Advisories

WDPN31 PGTW 201500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (SAUDEL) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.8N 150.2E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 314 NM EAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 17W IS NOW INTENSIFYING. ANIMATED ENHANCED
INFRARED (EIR) SATELLITE IMAGERY DEPICTS EXPLOSIVE CENTRAL
CONVECTION, WITH CLOUD TOP TEMPERATURES AS COLD AS -86 DEGREES
CELSIUS, WRAPPING INTO THE LOW-LEVEL CIRCULATION CENTER.
SURROUNDING THIS CORE CONVECTION, OUTER FEEDER BANDS ARE SHOWING
INCREASING CURVATURE AND EXTENT. DESPITE THE PRESENCE OF MODERATE
NORTHEASTERLY SHEAR IN THE 850-400 MB LAYER, THE UPPER-LEVEL
OUTFLOW IS EXPANDING RADIALLY, INDICATING THAT THE SYSTEM IS
SUCCESSFULLY OVERCOMING THE SHEAR. A FORTUITOUS 201101Z ASCAT-B
PASS REVEALED UNFLAGGED 35-40 KT WINDS IN THE SOUTHEAST QUADRANT
AND CONFIRMED A WIND FIELD THAT IS GRADUALLY BECOMING MORE
SYMMETRIC. THE SURROUNDING ENVIRONMENT IS FAVORABLE FOR FURTHER
DEVELOPMENT, CHARACTERIZED BY VERY WARM SEA SURFACE TEMPERATURES
(SST) OF 30-31 DEGREES CELSIUS AND RICH, DEEP-LAYER MOISTURE. THE
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
WELL-DEFINED CIRCULATION CENTER IN THE ASCAT-B PASS. THE INITIAL
INTENSITY HAS BEEN RAISED TO 40 KTS, ALSO WITH HIGH CONFIDENCE,
BASED ON THE SAME SCATTEROMETER DATA. PGTW, KNES, RJTD, AND RCTP
HAVE PROVIDED SUBJECTIVE DVORAK FIXES OF T2.5, WHILE THE OBJECTIVE
ESTIMATES FROM CIMSS LAG SLIGHTLY BEHIND.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A LOW- TO
MID-LEVEL RIDGE CENTERED AT 43N 173E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 39 KTS AT 200540Z
   CIMSS ADT: 32 KTS AT 201210Z
   CIMSS AIDT: 32 KTS AT 201210Z
   CIMSS D-MINT: 31 KTS AT 200720Z
   CIMSS D-PRINT: 41 KTS AT 201140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 17W IS NOW MOVING NORTHWESTWARD AT 11 KTS,
A MOTION THAT WILL PERSIST FOR THE NEXT 36 HOURS UNDER THE STEERING
INFLUENCE OF A RIDGE POSITIONED TO ITS NORTHEAST. AFTER TAU 36, A
DEEP-LAYER RIDGE OVER THE CENTRAL NORTH PACIFIC WILL MIGRATE
WESTWARD, INDUCING A MORE WESTWARD TRACK. COMPLICATIONS ARISING
FROM THE INTERACTION OF A MONSOON DEPRESSION, DESIGNATED AS 94W,
WITH THE SUBTROPICAL RIDGE (STR) OVER HONSHU RESULT IN SIGNIFICANT
FORECAST TRACK UNCERTAINTY AT TAU 96 AND TAU 120. A SPECTRUM OF
POSSIBLE TRACKS EXIST THAT DEPEND ON THE STRENGTH OF THE STR. ON
ONE END OF THE SPECTRUM, THE MONSOON DEPRESSION REMAINS WEAK,
ALLOWING FOR A STRONGER STR. THIS WOULD LEAD TO A ZONAL TRAJECTORY
TOWARD THE SOUTHERN RYUKYU ISLANDS. THE OTHER END PRESENTS A
STRONGER 94W, WHICH CREATES A WEAKNESS IN THE STR THAT WOULD ALLOW
TS 17W TO TURN POLEWARD INTO SHIKOKU. THE JTWC FORECAST TRACK
FAVORS THE FORMER SOLUTION AND DEPICTS A MORE ZONAL TRACK. THE
CONVECTION ASSOCIATED WITH TS 17W IS EXPANDING RAPIDLY, AND THE
SYSTEM IS ON THE PRECIPICE OF A PROLONGED PERIOD OF VERY RAPID
INTENSIFICATION (RI). THE ENVIRONMENTAL CONDITIONS ONLY GET BETTER
FROM THIS POINT FORWARD, WITH OCEAN HEAT CONTENT (OHC) INCREASING
TO 125-150 KJ PER CM2 AND VERTICAL WIND SHEAR (VWS) DECREASING TO
5-10 KTS. ADDITIONALLY, AFTER TAU 12, THE SYSTEM WILL TAP INTO A
POLEWARD OUTFLOW CHANNEL CREATED BY AN UPPER-LEVEL TROUGH. AS THE 
SYSTEM BECOMES MORE SYMMETRIC AND THE INNER CORE CONSOLIDATES, THESE
FACTORS WILL FUEL VERY RAPID INTENSIFICATION TO A PEAK NEAR SUPER
TYPHOON (STY) STATUS. THE SHIPS RI INDEX GIVES A 60 PERCENT
PROBABILITY OF A 65 KT INCREASE IN WIND SPEED OVER THE NEXT 24
HOURS ALONE. ACHIEVING STY INTENSITY IS WELL WITHIN THE REALM OF
POSSIBILITY, GIVEN THE HIGHLY FAVORABLE CONDITIONS AND A MAXIMUM
POTENTIAL INTENSITY OF 135 KTS. AFTER PEAKING AROUND TAU 60-72, THE
SYSTEM WILL ENTER A LESS FAVORABLE ENVIRONMENT OF HIGHER SHEAR AND
LOWER OHC, LEADING TO SUBSEQUENT WEAKENING. EYEWALL REPLACEMENT
CYCLES MAY ALSO BEGIN NEAR PEAK INTENSITY, WHICH WOULD INTRODUCE
LESS PREDICTABLE FLUCTUATIONS IN INTENSITY AND AN EXPANDED WIND
FIELD.

MODEL DISCUSSION: WITH A CROSS-TRACK SPREAD OF LESS THAN 100 NM AT
TAU 48, THE SHORT-TERM MODEL SOLUTIONS ARE IN GOOD AGREEMENT.
HOWEVER, CONFIDENCE IN THE LONG-TERM FORECAST IS LOW, AS THE
DIVERGENCE IN THE MODEL TRACKERS INCREASES TO 260 NM AT TAU 96 AND
430 NM AT TAU 120. THE SIGNIFICANT SPREAD IS DRIVEN BY TWO MODEL
CAMPS. THE ECMWF AND THE AI MODEL SOLUTIONS HAVE SHIFTED EVEN
FURTHER WESTWARD, BRINGING THE SYSTEM DIRECTLY OVER OR SOUTH OF
OKINAWA BEYOND TAU 120. THE HAFS-A, GFS, NAVGEM, JGSM, AND GALWEM
MODELS CONTINUE TO FAVOR A MORE POLEWARD TRACK TOWARD THE NORTHERN
RYUKYU ISLANDS, KYUSHU, OR SHIKOKU. THE JTWC FORECAST TRACK IS
POSITIONED NEAR THE JTWC CONSENSUS (CONW) THROUGH TAU 48 WITH HIGH
CONFIDENCE. THEREAFTER, IT HEDGES CLOSER TO THE AI CONSENSUS WITH
LOW CONFIDENCE. IT IS POSSIBLE THAT SUBSEQUENT FORECASTS WILL NEED
TO SHIFT FURTHER SOUTHWARD IN THE LONG TERM IF THIS TREND
CONTINUES. GIVEN THE RECENT IMPROVEMENTS IN THE SATELLITE
PRESENTATION OF TS 17W, RAPID INTENSIFICATION IS IMMINENT, IF NOT
ALREADY OCCURRING. THE INTENSITY FORECAST IS NOW MORE AGGRESSIVE,
CALLING FOR A 75 KT INCREASE OVER THE NEXT 48 HOURS TO A PEAK OF
125 KTS. WHILE THIS FORECAST IS AT THE UPPER END OF THE INTENSITY
GUIDANCE, COAMPS-TC IS EVEN MORE BULLISH WITH THE RATE OF
INTENSIFICATION. THE EXPERIMENTAL GOOGLE DEEPMIND MODEL ALSO PEAKS
AT 125 KTS, WITH NEARLY 40 PERCENT OF ITS ENSEMBLE MEMBERS
ACHIEVING STY STATUS. THE HAFS-A SOLUTION PEAKS AT 130 KTS.
REFLECTING THIS HIGH-END POTENTIAL, THE INTENSITY FORECAST HAS BEEN
INCREASED OUT TO TAU 72. BEYOND THIS POINT, NEARLY ALL OF THE
RELIABLE AIDS DEPICT A WEAKENING TREND, AND JTWC REFLECTS THIS.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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