Tropical Storm LEEPI (13W)

WTPN32 PGTW 062100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL STORM 13W (LEEPI) WARNING NR 012//
RMKS/
1. TROPICAL STORM 13W (LEEPI) WARNING NR 012    
   02 ACTIVE TROPICAL CYCLONES IN NORTHWESTPAC
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
   WIND RADII VALID OVER OPEN WATER ONLY
    ---
   WARNING POSITION:
   061800Z --- NEAR 39.2N 153.4E
     MOVEMENT PAST SIX HOURS - 055 DEGREES AT 22 KTS
     POSITION ACCURATE TO WITHIN 060 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   BECOMING EXTRATROPICAL
   RADIUS OF 034 KT WINDS - 040 NM NORTHEAST QUADRANT
                            040 NM SOUTHEAST QUADRANT
                            000 NM SOUTHWEST QUADRANT
                            000 NM NORTHWEST QUADRANT
   REPEAT POSIT: 39.2N 153.4E
    ---
   FORECASTS:
   12 HRS, VALID AT:
   070600Z --- 42.0N 158.1E
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   EXTRATROPICAL
   RADIUS OF 034 KT WINDS - 000 NM NORTHEAST QUADRANT
                            060 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            000 NM NORTHWEST QUADRANT
   VECTOR TO 24 HR POSIT: 050 DEG/ 30 KTS
    ---
   24 HRS, VALID AT:
   071800Z --- 45.7N 164.5E
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   EXTRATROPICAL
    ---
REMARKS:
062100Z POSITION NEAR 39.9N 154.6E.
06SEP24. TROPICAL STORM 13W (LEEPI), LOCATED APPROXIMATELY 567 NM
EAST OF MISAWA, JAPAN, HAS TRACKED NORTHEASTWARD AT 22 KNOTS OVER
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY 
DEPICTS A SMALL AND SHALLOW LOW LEVEL CIRCULATION CENTER (LLCC), 
MOVING RAPIDLY NORTHEASTWARD UNDER STRONG UPPER-LEVEL SOUTHWESTERLY 
FLOW INDICATED BY A BROAD REGION OF CIRRUS STREAMERS. MANUAL AND 
AUTOMATED PHASE CLASSIFICATION WORKSHEETS AS WELL AS A FSU PHASE SPACE 
DIAGRAM SHOW THE SYSTEM AS A SUBTROPICAL OR HYBRID, SYSTEM, WITH 
CHARACTERISTICS OF BOTH A TROPICAL AND EXTRATROPICAL LOW. THE JTWC 
ASSESSMENT IS THAT THE SYSTEM IS UNDERGOING EXTRATROPICAL TRANSITION 
(ETT), HAVING CROSSED NORTH OF THE 26C ISOTHERM, MOVING INTO A 
BAROCLINIC ZONE AND THERMAL RIBBON, AND EMBEDDING IN PHASE WITH A 
500MB SHORTWAVE TROUGH. THE SYSTEM WILL CONTINUE TO ACCELERATE 
NORTHEASTWARD WHILE UNDERGOING ETT, WHILE MAINTAINING ITS CURRENT 
INTENSITY OF 35 KNOTS. FULL TRANSITION TO A WEAK GALE-FORCE LOW 
PRESSURE AREA IS EXPECTED WITHIN THE NEXT 12 HOURS. THIS IS THE FINAL 
WARNING ON THIS SYSTEM BY THE JOINT TYPHOON WRNCEN PEARL HARBOR HI. 
THE SYSTEM WILL BE CLOSELY MONITORED FOR SIGNS OF REGENERATION. 
MINIMUM CENTRAL PRESSURE AT 061800Z IS 1003 MB. MAXIMUM SIGNIFICANT 
WAVE HEIGHT AT 061800Z IS 16 FEET. REFER TO TYPHOON 12W (YAGI) 
WARNINGS (WTPN31 PGTW) FOR SIX-HOURLY UPDATES.
//
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WDPN32 PGTW 061500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (LEEPI)        
WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 37.9N 151.1E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 484 NM EAST-SOUTHEAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
THE SYSTEM HAS ALL BUT FALLEN APART WHEN VIEWED ON ANIMATED ENHANCED 
INFRARED (EIR) SATELLITE IMAGERY, BUT A CAREFUL ANALYSIS REVEALS A 
PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) STILL INTACT. A 
061051Z AMSU-B 89 GHZ MICROWAVE IMAGE ALSO HINTS AT SHALLOW, CURVED 
BANDS WRAPPING AROUND THE FULLY CLOSED LLCC POSITION, SUPPORTING THE 
ASSESSED POSITION WITH HIGH CONFIDENCE. AT 061200Z, EIR IMAGERY SHOWS 
A SINGLE CONVECTIVE BURST ORIGINATING IN THE SOUTHEAST QUADRANT WITH 
ASSOCIATED OUTFLOW SHEARING IN THE EQUATORWARD DIRECTION. ASIDE FROM 
THIS, GENERALLY SPARSE OUTFLOW IS NOTED DUE TO THE BULK OF THE UPPER 
LEVEL CLOUDS HAVING ALREADY DEPARTED EQUATORWARD OR DISSIPATED IN 
RECENT TAUS. A 061133Z ASCAT PARTIAL PASS IMAGE SHOWS WINDS OF 20-25 
KTS ALONG THE SOUTHWESTERN PERIPHERY, BUT RECENT SCATTEROMETRY IS NOT 
AVAILABLE NEAR THE LLCC OR ALONG THE EASTERN SIDE OF THE SYSTEM WHERE 
THE STRONGER WINDS ARE PRESUMED TO BE. THE BEST OBJECTIVE-ESTIMATED 
VALUE USING A COMBINED ADT (27 KTS) AND AIDT (38 KTS) IS 35 KTS, 
SUPPORTING THE ASSESSED INTENSITY WITH MEDIUM CONFIDENCE.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP LAYER STR TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T1.5 - 25 KTS
   CIMSS ADT: 27 KTS AT 1200Z
   CIMSS AIDT: 38 KTS AT 1200Z
   CIMSS SATCON: 42 KTS AT 1300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 30+ KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: ALTHOUGH ANIMATED EIR SATELLITE IMAGERY HAS
REVEALED A FADING APPEARANCE OF TS 13W, THE LLCC WILL CONTINUE
WRAPPING INTO ITSELF OVER THE NEXT 24 HOURS IN THE LOWER LEVELS OF
THE TROPOSPHERE DUE TO CONSERVATION OF ANGULAR MOMENTUM. THE UPPER
PORTIONS OF THE SYSTEM WILL CONTINUE TO SHEAR AWAY FROM THE LLCC AS
TS LEEPI APPROACHES THE EQUATORWARD BOUNDS OF THE JETSTREAM.
VERTICAL WIND SHEAR (VWS) VALUES WILL REMAIN AT UNFAVORABLE LEVELS
AND CONTINUE TO WORSEN, WHILE SEA SURFACE TEMPERATURES (SSTS) COOL
FROM APPROXIMATELY 27C AT TAU 0 TO 22C BY TAU 24. INTERACTION WITH
A THERMAL RIBBON IS IMMINENT, WITH EXTRATROPICAL TRANSITION (ETT)
BEGINNING NEAR TAU 12. BY TAU 24, A COLD FRONT APPROACHING FROM THE
NORTHWEST WILL COLLIDE WITH THE SYSTEM, AT WHICH POINT IT WILL
COMPLETE ETT. NO FURTHER DEVELOPMENT IS EXPECTED WITHIN THE
FORECAST PERIOD, HOWEVER, THE SYSTEM IS FORECAST TO MAINTAIN AN
INTENSITY OF 35 KTS DUE TO A COMBINATION OF FACTORS THAT INCLUDE
ITS PROXIMITY TO STRONG RIDGING TO THE EAST, LEADING TO
GRADIENT-INDUCED WINDS ALONG THE EAST SIDE, AND COMPOUNDED BY THE
ACCELERATING FORWARD SPEEDS (APPROXIMATELY 17-23 KTS).

MODEL DISCUSSION: GFS ENSEMBLE MODEL (GEFS) GUIDANCE CONTINUES TO
DEMONSTRATE A VERY TIGHT AGREEMENT AMONG MEMBERS, WITH A STRAIGHT
AND ACCELERATING NORTHEASTWARD TRACK DEPICTED. OTHER MODELS ARE
STARTING TO LOSE TRACK OF THE SYSTEM AS THE SIGNAL BECOMES
CONTAMINATED BY MID-LATITUDE INFLUENCES, BUT ALL RELIABLE NUMERICAL
MODEL GUIDANCE HAS SHOWN CONSISTENTLY VERY GOOD AGREEMENT
CONCERNING THE TRACK AND INTENSITY. THE INTENSITY CONSENSUS (ICNW)
PREDICTS A GRADUAL DECLINE, BUT NOT ENOUGH OF A WEAKENING TO DROP
BELOW THE CURRENT INTENSITY. CONFIDENCE REMAINS HIGH FOR BOTH THE
JTWC TRACK AND INTENSITY FORECASTS.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: HIGH//
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