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JTWC/25W/#29/09-25 12Z Prognostic Reasoning
WDPN33 PGTW 251500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (NEOGURI) WARNING NR
029//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
INITIAL POSITION: 32.4N 154.9E
INITIAL INTENSITY: 60 KTS
GEOGRAPHIC REFERENCE: 776 NM EAST OF YOKOSUKA, JAPAN
MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 11 KTS
SIGNIFICANT WAVE HEIGHT: 28 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH LOW-LEVEL CLOUDS
TIGHTLY WRAPPING INTO THE LLCC AND ASSOCIATED PERSISTENT CONVECTION
CONFINED TO THE NORTHWESTERN QUADRANT. THE OVERALL APPEARANCE OF THE
STORM HAS DEGRADED OVER THE PAST 6 HOURS, LIKELY DUE TO UPWELLING
EFFECTS AND DIGNIFICANT DRY AIR ENTRAINMENT. ENVIRONMENTAL ANALYSIS
INDICATES THE ENVIRONMENT IS MARGINALLY FAVORABLE, CHARACTERIZED BY
LOW (10-15 KTS) VERTICAL WIND SHEAR, WARM (28-29 C) SEA SURFACE
TEMPERATURES, AND STRONG POLEWARD OUTFLOW, OFFSET BY THE UPWELLING
AND DRY AIR. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON A 251128Z METOP-B ASCAT IMAGE REVEALING THE LLCC. THE
INITIAL INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED
ON THE AGENCY DVORAK FIXES LISTED BELOW. ADDITIONALLY, A 250731Z RCM-
2 SAR WINDSPEED IMAGE REVEALED A SWATH OF 65-70 KTS IN THE NORTHERN
SEMICIRCLE. CIMSS OBJECTIVE ESTIMATES ARE ANALYZED TO BE TOO LOW DUE
TO THE WEAK CONVECTIVE STRUCTURE OF THE SYSTEM.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT BETWEEN
TWO SUBTROPICAL RIDGES (STR) OF EQUAL STRENGTH POSITIONED TO THE
EAST AND WEST OF THE SYSTEM
AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T4.0 - 65 KTS
RJTD: T3.5 - 55 KTS
RCTP: T3.0 - 45 KTS
KNES: T3.5 - 55 KTS
CIMSS ADT: 35 KTS AT 251140Z
CIMSS AIDT: 41 KTS AT 251140Z
CIMSS D-PRINT: 43 KTS AT 251210Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
VWS: 10-15 KTS
SST: 28-29 CELSIUS
OUTFLOW: STRONG POLEWARD
OTHER FACTORS: UPWELLING AND DRY AIR ENTRAINMENT
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: TROPICAL STORM (TS) 25W IS FORECAST TO
CONTINUE TRACKING SOUTHWESTWARD THROUGH TAU 24, THEN BECOMING
QUASI-STATIONARY FROM TAU 24 TO TAU 36. WHILE THE STORM IS
QUASI-STATIONARY, ERRATIC MOTION NOT REFLECTED IN THE FORECAST MAY
OCCUR. AFTER TAU 36, 25W IS EXPECTED TO LOOP BACK TO THE NORTHEAST
AND
CONTINUE A NORTHEASTWARD TRACK MOTION UNTIL IT BECOMES FULLY
EXTRATROPICAL NEAR TAU 72. BEGINNING AROUND TAU 48, 25W WILL
SIGNIFICANTLY ACCELERATE AS IT ENTERS UNDER THE INFLUENCE OF THE
UPPER-LEVEL JET AND WILL BEGIN EXTRATROPICAL TRANSITION (ETT) AT THAT
TIME. REGARDING INTENSITY, 25W IS FORECAST TO SLIGHTLY WEAKEN BETWEEN
TAUS 12-24 TO 55 KTS. INTENSITY IS FORECAST TO INCREASE TO 60-70 KTS
AS 25W MOVES NORTHEASTWARD DURING ETT AND POLEWARD OUTFLOW BECOMES
MORE ROBUST IN RESPONSE TO INTERACTION WITH THE JET.
MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN STRONG
AGREEMENT THROUGH TAU 48, WITH ALL MODELS CONTINUING TO SHOW 25W
LOOPING OVER ITS PREVIOUS TRACK. AFTER TAU 48, THE GUIDANCE BEGINS
TO DEVIATE. AT TAU 72, THE ALONG-TRACK SPREAD IS APPROXIMATELY 320
NM AS JGSM AND GFS FORECAST FASTER TRACK SPEEDS THAN ECMWF AND UKMET,
WHICH LAG BEHIND. THE ALONG-TRACK SPREAD INJECTS SOME
UNCERTAINTY; HOWEVER, THE JTWC TRACK FORECAST IS STILL PLACED WITH
OVERALL MEDIUM CONFIDENCE. RELIABLE INTENSITY IS IN GOOD AGREEMENT IN
SLIGHT WEAKENING BETWEEN TAUS 12-24, BEFORE REINTENSIFYING WHILE
UNDERGOING ETT BETWEEN TAUS 48-72; HOWEVER, THERE IS SOME
DISAGREEMENT ON THE PEAK INTENSITY BEFORE 25W BECOMES FULLY
EXTRATROPICAL. AS A RESULT, THE JTWC INTENSITY FORECAST IS PLACED
WITH OVERALL MEDIUM CONFIDENCE.
FORECAST CONFIDENCE:
TRACK 00-72 HR: MEDIUM
INTENSITY 00-72 HR: MEDIUM//
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