Tropical Storm PAKHAR Advisory Mon Dec 12

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 29W (PAKHAR) WARNING NR
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 20.0N 130.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 408 NM SOUTH-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
HAVING REACHED A PEAK OF 50 KNOTS, TROPICAL STORM 29W (PAKHAR) HAS
NOW STARTED ON THE PATH TOWARDS A SLOW DEMISE. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE REMNANTS OF THE
CENTRAL DENSE OVERCAST (CDO) WITH OVERSHOOTING TOPS SEEN JUST SIX
HOURS AGO, HAS ALREADY STARTED TO DECOUPLE FROM THE LOW LEVEL
CIRCULATION CENTER (LLCC) AND RACE DOWNSTREAM TO THE NORTHEAST,
LEAVING THE LLCC LANGUISHING IN THE DUST. HOWEVER, WHILE THE GENERAL
SCENARIO IS EVIDENT FROM THE MSI, FINDING THE LLCC IS PROVING TO BE
A CHALLENGE, AS IT IS BEGINNING TO ELONGATE AND IS TILL OBSCURED BY
UPPER-LEVEL CIRRUS CLOUDS. SOME LOW-LEVEL BANDS STREAMING UP FROM
THE SOUTH ARE EVIDENT NEAR THE 130.5E, SUGGESTING THE LLCC MUST BE
WEST OF THAT LINE, WHILE LOW LEVEL STRATOCUMULUS CLOUDS ARE POURING
SOUTH-SOUTHWESTWARD INTO THE REAR OF THE SYSTEM INDICATING THE
PRESENCE OF RELATIVELY DRY AND STABLE AIR TO THE WEST. A 120458Z
AMSR2 36GHZ MICROWAVE IMAGE SHOWS AN ELONGATED AND DISORGANIZED LLC
TO THE SOUTHWEST OF THE DEEP CONVECTION. ADDITIONALLY, REANALYSIS OF
THE 120030Z ASCAT-B AMBIGUITIES RESULTED IN A SLOWER TRACK SPEED OVER
THE PAST SIX HOURS. THE INITIAL POSITION IS ASSESSED WITH LOW
CONFIDENCE DUE TO THE LACK OF A CLEAR-CUT LLCC IN THE AVAILABLE
IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE,
ROUGHLY AT THE AVERAGE OF THE AGENCY FIXES, BUT LOWER THAN THE
OBJECTIVE ADT CI, THOUGH THE ADT FINAL-T IS DOWN TO T3.1, WHICH
SUPPORTS THE INITIAL INTENSITY QUITE WELL. THE SYSTEM SITS ON THE
WESTERN END OF A SURFACE FRONT AS WELL, WHICH EXTENDS OUT TO THE EAST.
THE SYSTEM HAS REACHED THE SHARP SHEAR BOUNDARY, WITH CIMSS SHEAR
ESTIMATES NOW ABOVE 25 KNOTS FROM THE SOUTHWEST, WHICH SUPPORTS THE
DEPICTION IN THE MSI. WHILE SSTS ARE WARM ENOUGH TO SUPPORT
DEVELOPMENT, THE HIGH SHEAR AND SIGNIFICANT DRY, STABLE AIR INTRUSION
FROM THE WEST DO NOT SUPPORT ANY ADDITIONAL DEVELOPMENT.
INITIAL WIND RADII BASIS: SCATTEROMETER DATA
CURRENT STEERING MECHANISM: NORTHWEST PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE EAST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 51 KTS AT 120447Z
   CIMSS ADT: 57 KTS AT 120540Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR INTRUSION FROM THE WEST. WEAK EQUATORWARD
OUTFLOW.
ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: HIGH
   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 PRIMARY STEERING INFLUENCE CURRENTLY
REMAINS THE WEST-NORTHWEST SIDE OF THE DEEP STR CENTERED FAR TO THE
EAST. THIS IS IN THE PROCESS OF CHANGING HOWEVER, NOW THAT THE
SYSTEM IS STARTING TO DECOUPLE. HIGH-RESOLUTION HWRF POTENTIAL
VORTICITY CROSS-SECTIONS REVEAL THE LLCC ONLY EXTENDS UP TO ABOUT
THE 850MB LEVEL AND IS ALREADY COMPLETELY DECOUPLED FROM THE
MID-LEVEL VORTEX. AS SUCH, THE STEERING LEVEL IS LIKELY ALREADY
DOWN TO ABOUT THE 850MB LAYER. WITH THE PRESENCE OF THE FRONTAL
SYSTEM JUST TO THE NORTH ALONG ABOUT 20N AND THE RELATIVELY STRONG
NORTH-NORTHEAST FLOW BEHIND IT, TS 29W HAS RUN INTO A WALL AND WILL
NOT BE ABLE TO PUSH MUCH FURTHER POLEWARD BEFORE TURNING SHARPLY
EAST OVER THE NEXT 12 HOURS. AS THE SYSTEM CONTINUES TO WEAKEN, THE
STRONG NORTHEASTERLY FLOW TO THE NORTH WILL PUSH THE FRONTAL SYSTEM
FURTHER TO THE SOUTH AND THE REMNANTS OF TS 29W WILL TURN TO THE
SOUTHWEST, RUNNING ALONG AND AHEAD OF THE SOUTHERN EDGE OF THE
FRONTAL BOUNDARY. THE SYSTEM IS ULTIMATELY FORECAST TO FULLY
DISSIPATE NO LATER THAN TAU 48, THOUGH IT IS POSSIBLE THIS COULD
OCCUR SLIGHTLY EARLIER IN THE FORECAST PERIOD.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT,
WITH ALL THE MODELS EXCEPT THE COAMPS-TC AND UKMET ENSEMBLE,
AGREEING ON A TURN FIRST TO THE EAST AND THEN TO THE SOUTHWEST OVER
THE COURSE OF THE FORECAST. THERE REMAIN SOME DIFFERENCES IN THE
TIMING AND SHARPNESS OF THE TURN, WITH THE GFS CONTINUING TO SHOW
THE EARLIEST AND SHARPEST TURN WHILE THE NAVGEM IS THE SLOWEST AND
MOST GRADUAL. THE REMAINDER OF THE CONSENSUS MEMBERS LIE IN A
NARROW ENVELOPE ROUGHLY BETWEEN THE TWO OUTLIERS. THE JTWC
FORECAST TRACK LIES AMONGST THE BULK OF THE GUIDANCE IN THE TIGHTLY
PACKED ENVELOPE, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN
GOOD AGREEMENT, WITH ALL MODELS SHOWING STEADY AND RAPID WEAKENING
THROUGH THE FORECAST PERIOD, LENDING HIGH CONFIDENCE TO THE JTWC
FORECAST INTENSITY.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: HIGH//
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