Advisories

WDPN31 PGTW 210900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (SAUDEL) WARNING NR 
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.9N 148.5E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 221 NM EAST-NORTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 17W IS UNDERGOING RAPID INTENSIFICATION (RI)
AND IS ON THE VERGE OF ATTAINING TYPHOON STATUS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A DEEP CONVECTIVE
BAND ALONG THE EASTERN PERIPHERY THAT HAS WRAPPED OVER THE
LOW-LEVEL CIRCULATION CENTER (LLCC). IN THE MOST RECENT FRAMES, A
WARM SPOT HAS APPEARED NEAR THE CENTER, SURROUNDED BY HOT TOWERS,
INDICATING THAT AN INNER CORE IS RAPIDLY CONSOLIDATING. THIS
DEVELOPMENT IS SUPPORTED BY A HIGHLY FAVORABLE ENVIRONMENT
CHARACTERIZED BY HIGH OCEAN HEAT CONTENT (OHC), RICH DEEP-LAYER
MOISTURE, AND LOW VERTICAL WIND SHEAR (VWS). THERE HAS BEEN NO
HIGH-RESOLUTION MICROWAVE IMAGERY IN THE PAST 08 HOURS TO CLARIFY
THE CORE STRUCTURE. HOWEVER, A 202334Z ASCAT-B PASS REVEALED A
SWATH OF 45-50 KT WINDS IN THE EASTERN SEMICIRCLE AND AN LLCC THAT
IS BECOMING MORE SYMMETRIC. SINCE THEN, THE SYSTEM HAS BECOME
SIGNIFICANTLY BETTER DEFINED, AND THE SUBJECTIVE AND OBJECTIVE
INTENSITY ESTIMATES HAVE RISEN. THE INITIAL POSITION IS ASSESSED
WITH HIGH CONFIDENCE BASED ON THE CENTER CLEARING IN THE MSI. THE
INITIAL INTENSITY HAS BEEN RAISED TO 60 KTS WITH HIGH CONFIDENCE
BASED ON A BLEND OF THE T3.5-4.0 AGENCY DVORAK FIXES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A SUBTROPICAL
RIDGE (STR) CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 57 KTS AT 210510Z
   CIMSS ADT: 49 KTS AT 210610Z
   CIMSS AIDT: 43 KTS AT 210610Z
   CIMSS D-MINT: 43 KTS AT 210312Z
   CIMSS D-PRINT: 60 KTS AT 210540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 17W IS MOVING NORTHWESTWARD ALONG THE
SOUTHWESTERN PERIPHERY OF A DEEP-LAYER RIDGE CENTERED OVER THE
CENTRAL NORTH PACIFIC. THIS MOTION WILL CONTINUE THROUGH TAU 24,
AFTER WHICH TIME, THE STEERING RIDGE WILL MIGRATE WESTWARD AND
INITIATE A MORE ZONAL TRACK TOWARD THE WEST. TRACK CONFIDENCE
DECREASES SIGNIFICANTLY AFTER TAU 72, ATTRIBUTED TO UNCERTAINTY IN
THE EVOLUTION OF A MONSOON DEPRESSION, DESIGNATED AS 94W, OVER THE
EAST CHINA SEA. ON ONE END OF THE SPECTRUM, A STRONGER 94W WOULD
RESULT IN A WEAK STR OVER HONSHU AND INDUCE A MORE POLEWARD TRACK.
ON THE OTHER HAND, A WEAKER 94W WOULD KEEP THE STR LARGELY
UNAFFECTED. THE STR WOULD STEER THE SYSTEM ALONG A MORE ZONAL
TRAJECTORY TOWARD THE RYUKYU ISLANDS. THIS LATTER SCENARIO IS
FAVORED BY JTWC. THE AFOREMENTIONED, HIGHLY FAVORABLE ENVIRONMENTAL
CONDITIONS WILL PERSIST THROUGH TAU 48 AND FUEL A HIGH RATE OF
INTENSIFICATION. THE FORECAST CALLS FOR TS 17W TO ACHIEVE AT LEAST
120 KTS BY TAU 48. THEREAFTER, INTENSIFICATION WILL CEASE DUE TO A
COMBINATION OF EYEWALL REPLACEMENT CYCLES (ERC) AND LOWER OHC.
INCREASING VWS AND EVEN LOWER OHC WILL INITIATE WEAKENING BEYOND
TAU 72. IT IS IMPORTANT TO NOTE THAT, WHILE THE FORECAST HOLDS THE
INTENSITY AT 120 KTS FROM TAU 48 TO TAU 72, FLUCTUATIONS MAY OCCUR
AS A RESULT OF ERC.

MODEL DISCUSSION: MODELS ARE IN EXCELLENT AGREEMENT THROUGH TAU 72
WITH A CROSS-TRACK SPREAD OF 70 NM, WHICH LENDS HIGH CONFIDENCE TO
THE SHORT-TERM JTWC FORECAST TRACK. THE UNCERTAINTY ENVELOPE AT TAU
120 NOW EXCLUDES SHIKOKU AND LARGELY KYUSHU, SPANNING THE SOUTHERN
TO THE NORTHERN RYUKYU ISLANDS. THE FORECAST TRACK IS POSITIONED
BETWEEN THE JTWC CONSENSUS (CONW) AND THE AI CONSENSUS THROUGH TAU
72 AND THEN LEANS CLOSER TO THE AI CONSENSUS FOR THE EXTENDED
PERIOD. THE RELIABLE INTENSITY AIDS DEPICT RI THROUGH TAU 36. THE
EXPERIMENTAL GOOGLE DEEPMIND IS THE MOST AGGRESSIVE, PREDICTING A
50 KT INCREASE OVER THE NEXT 24 HOURS. THE SHIPS RI INDEX ESTIMATES
A 55 PERCENT CHANCE OF A 45 KT INCREASE OVER THE NEXT 36 HOURS AND
A 58 PERCENT CHANCE OF A 65 KT INCREASE OVER THE NEXT 72 HOURS. THE
HAFS-A AND DEEPMIND SOLUTIONS DEPICT A PEAK INTENSITY OF 120 KTS.
THE JTWC INTENSITY FORECAST REFLECTS A SLIGHTLY LESS AGGRESSIVE
RATE OF DEVELOPMENT THAN DEEPMIND BUT STILL CALLS FOR THE 120 KT
PEAK. MOST OF THE MODELS GENERALLY DEPICT GRADUAL TO STEADY
WEAKENING BEYOND TAU 72, AND THE INTENSITY FORECAST FOLLOWS SUIT.

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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