Advisories

WDPN32 PGTW 100300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (PEILOU) WARNING NR 
013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.5N 148.3E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 452 NM NORTH-NORTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: EASTWARD AT 24 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 13W (PEILOU) AS A SMALL SYSTEM WITH PERSISTENT CONVECTION 
JUST NORTHEAST OF THE ASSESSED LOW LEVEL CIRCULATION CENTER (LLCC) AS 
WELL AS A STRONG CONVECTIVE BAND CURVING OFF TO THE SOUTHWEST, 
SPANNING ACROSS THE NORTHERN MARIANAS. ENVIRONMENTAL ANALYSIS REVEALS 
FAVORABLE CONDITIONS OF LOW (5-10 KTS) VERTICAL WIND SHEAR, WARM (29-
30 C) SEA SURFACE TEMPERATURES, AND AN UPPER-LEVEL TROUGH POSITIONED 
TO THE NORTHWEST OF TS 13W AIDING IN THE UPPER LEVEL OUTFLOW, 
OBSERVABLE IN MSI. THE INITIAL POSITION IS ASSESSED WITH MEDIUM 
CONFIDENCE BASED ON THE PARTIALLY EXPOSED WESTERN FLANK OF THE LLCC IN 
MSI. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON 
AGREEMENT BETWEEN AGENCY DVORAK FIXES AND CIMSS OBJECTIVE ESTIMATES 
LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: LOW-LEVEL MONSOONAL FLOW AND EASTERN
EXTENSION OF A NEAR EQUATORIAL RIDGE (NER) CENTERED TO THE
SOUTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.5 - 35 KTS
   CIMSS ADT: 43 KTS AT 092330Z
   CIMSS AIDT: 37 KTS AT 092330Z
   CIMSS D-PRINT: 31 KTS AT 092330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: UPPER-LEVEL TROUGH POSITIONED TO THE NORTHWEST

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   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 13W IS FORECAST TO CONTINUE ON AN EAST-
NORTHEASTWARD TRACK OUT TO TAU 12 BEFORE TAKING A MORE POLEWARD TURN 
AS IT REMAINS UNDER THE STEERING INFLUENCE OF THE STRONG LOW-LEVEL 
MONSOONAL FLOW AND, TO A LESSER EXTENT, THE EASTERN EXTENSION OF A 
NEAR EQUATORIAL RIDGE (NER) CENTERED TO THE SOUTHWEST, WITH BOTH 
CONTRIBUTING TO THE SAME RESULTANT TRACK. REGARDING INTENSITY, TS 13W 
IS CURRENTLY IN AN AREA OF INCREASED OUTFLOW ALOFT THANKS TO THE 
UPPER-LEVEL TROUGH POSITIONED TO THE NORTHWEST, HOWEVER THIS TROUGH IS 
EXPECTED TO PASS OVER TS 13W AND RETREAT BY TAU 36 AT WHICH POINT THE 
SYSTEM IS EXPECTED TO EXPERIENCE INCREASED NORTHWESTERLY SHEAR CAUSED 
BY STRONG UPPER LEVEL WESTERLIES AND ENSUING DRY AIR ENTRAINMENT. 
THEREFORE, TS 13W IS FORECAST TO BEGIN A WEAKENING TREND AT TAU 24 AND 
ULTIMATELY DISSIPATE BY TAU 60.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT FOR THE
REMAINDER OF THE FORECAST PERIOD WITH A CROSS TRACK SPREAD OF 140
NM AT TAU 60. MODEL TRACK SPEED HAS ALSO COME INTO BETTER AGREEMENT, 
WITH THE ONLY OUTLIER OF NAVGEM BEING EXCLUDED AS MUCH SLOWER, ALONG 
TRACK SPREAD IS 85 NM AT TAU 60. THE OFFICIAL JTWC FORECAST TRACK IS 
PLACED WITH HIGH CONFIDENCE, IN LINE WITH THE MULTI-MODEL CONSENSUS 
AND SLIGHTLY FASTER MORE IN ACCORDANCE WITH THE AI CONSENSUS. 
INTENSITY MODEL GUIDANCE HAS ALSO COME INTO BETTER AGREEMENT WITH 
DECAY-SHIPS (GFS BASED) REMAINING THE ONLY OUTLIER WITH A GRADUAL 
INTENSIFICATION TREND OUT TO TAU 96, THE REMAINDER OF GUIDANCE AGREES 
ON A GENERAL WEAKENING PHASE BEYOND TAU 24. THE OFFICIAL JTWC FORECAST 
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, CLOSELY IN LINE WITH THE 
MULTI-MODEL CONSENSUS OUT TO TAU 36 BUT THEN DIVERGING FROM THE BULK 
OF GUIDANCE EXPECTING DISSIPATION BY TAU 60, IN LINE WITH ALL GLOBAL
DETERMINISTIC MODEL FIELDS WHICH PICTURE TS 13W OPENING INTO A
TROUGH BY THAT POINT.

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