WDPN31 PGTW 032100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.0N 145.0E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 464 NM SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 04W (MUN) PRESENTS AS A VERY COMPACT SYSTEM,
BECOMING INCREASINGLY ISOLATED FROM ITS ENVIRONMENT IN ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY. DEEP CONVECTIVE ACTIVITY
HAS BLOOMED OVERNIGHT, ORGANIZED INTO A SMALL CDO FEATURE AND
REACHED ITS PEAK IN TERMS OF COLDEST CLOUD TOP TEMPERATURES AT
AROUND 031700Z, FOLLOWED BY RAPID WARMING IN THE SUBSEQUENT HOURS.
A 031628Z AMSR2 COLOR-ENHANCED 89GHZ IMAGE DEPICTS WELL-ORGANIZED
LOW-LEVEL BANDING FEATURES WRAPPING INTO SHARPLY OUTLINED LOW LEVEL
CIRCULATION CENTER (LLCC). CONVECTIVELY HOWEVER, THE SYSTEM IS
HIGHLY ASYMMETRIC, WITH SIGNIFICANT CONVECTIVE ACTIVITY ISOLATED TO
THE NORTH AND EASTERN PORTIONS OF THE CIRCULATION, PRIMARILY DUE TO
THE INFLUENCE OF PERSISTENT MID-LEVEL DRY AIR ACROSS THE
SOUTHWESTERN PORTION OF THE CIRCULATION. A 031901Z SSMIS 91GHZ
IMAGE CONFIRMS THE STRUCTURAL ASYMMETRIES, AND AN ARCHER ANALYSIS
OF SAID MICROWAVE IMAGE SUPPORTS THE INITIAL POSITION WITH HIGH
CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE, ASSESSED SIGNIFICANTLY HIGHER THAN ALL OF THE OBJECTIVE
INTENSITY ESTIMATES, WHICH ARE LIKELY UNDER-ESTIMATING THE
INTENSITY (BASED ON EARLIER SAR AND ASCAT DATA) DUE TO THE SMALL
SIZE OF THE SYSTEM AND SLIGHTLY HIGHER THAN THE MOST AGGRESSIVE
SUBJECTIVE DVORAK CI ESTIMATES. THE ENVIRONMENT IS MARGINALLY
FAVORABLE, CHARACTERIZED BY WARM SSTS, AND LOW SHEAR. HOWEVER, THE
PRESENCE OF AN UPPER-LEVEL CYCLONIC ROTATION OVER TOP OF THE
SYSTEM, AS REVEALED IN ANIMATED WATER VAPOR IMAGERY AS WELL AS
CIMSS AMV AND CIRA DMW PRODUCTS IS SQUASHING UPPER-LEVEL OUTFLOW
FOR THE TIME BEING. FURTHERMORE, THE SYSTEM CONTINUES TO STRUGGLE WITH 
THE LINGERING EFFECTS OF DRY MID-LEVEL AIR PERSISTING ACROSS HALF OF 
THE CIRCULATION.

INITIAL WIND RADII BASIS: PERSISTENCE

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYERED
SUBTROPICAL RIDGE (STR) COMPLEX EXTENDING FROM THE CENTRAL
PHILIPPINES, EASTWARD TO THE CENTRAL MARIANAS, AND THEN
NORTHEASTWARD TO NEAR 30N 160E. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 47 KTS AT 031600Z
   CIMSS ADT: 39 KTS AT 031800Z
   CIMSS AIDT: 41 KTS AT 031800Z
   CIMSS D-MINT: 37 KTS AT 031630Z
   CIMSS D-PRINT: 39 KTS AT 031830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: CYCLONIC CIRCULATION OVER TOP OF THE CIRCULATION
AS WELL AS DRY MID-LEVEL AIR OVER THE SOUTHWESTERN PORTION OF THE
SYSTEM. 

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: OVER THE PAST SIX HOURS, TS 04W HAS SLOWED
DOWN A GOOD BIT, WHILE WOBBLING SLOWLY AS IT MOVES INTO A SLIGHTLY
WEAKER STEERING FLOW. THE RIDGE COMPLEX TO THE EAST IS STARTING TO
BREAK OFF INTO DISTINCT CENTERS OF ANTICYCLONIC FLOW, WITH THE MAIN
AREA OF INTEREST FOCUSED OVER THE NORTHERN MARIANAS. AS THIS
SUBTROPICAL RIDGE (STR) CENTER BUILDS, THE ENTIRE RIDGING PATTERN
FLATTENS OUT AS THE NORTHERN EXTENSION ERODES FROM THE NORTH. THIS
WILL ALLOW TS 04W TO SLOWLY SHIFT ONTO A MORE EAST-NORTHEASTWARD
TRACK FROM ABOUT TAU 12 THROUGH TAU 48. SIGNIFICANT WARM AIR
ADVECTION ACROSS A DEEP LAYER OF THE ATMOSPHERE DUE TO A DEEP
SOUTHWESTERLY SURGE FLOW WILL BUILD A BUBBLE-RIDGE TO THE EAST OF
TS 04W BY TAU 60, FORCING THE SYSTEM ONTO A MORE NORTHWARD TRACK FROM
THIS POINT THROUGH THE END OF THE FORECAST PERIOD. IF THE RIDGE
GETS STRONG ENOUGH, AS INDICATED IN SOME MODELS (GFS), IT COULD
BUILD WESTWARD AND RESULT IN A BIT MORE OF A NORTHWESTWARD TRACK
BETWEEN TAU 72 AND TAU 96. REGARDLESS, BY THE END OF THE FORECAST,
THE TRACK WILL SHIFT MORE TOWARDS THE NORTH-NORTHEAST ONCE MORE AS
THE REMNANT SYSTEM BEGINS TO BE PULLED INTO A BREAK IN THE RIDGE
AND INTO A MID-LATITUDE TROF PASSING TO THE NORTH. IN TERMS OF
INTENSITY, THE ISOLATION OF THE SYSTEM FROM ANY SIGNIFICANT SOURCE
OF OUTFLOW ALOFT, AND THE CONTINUED INFLUENCE OF DRY AIR, WILL
HINDER INTENSIFICATION IN THE NEAR TERM. UPPER-LEVEL OUTFLOW IS SET
TO IMPROVE AFTER TAU 18 WITH THE APPROACH OF A WEAK UPPER-LEVEL
TROF PROVIDING A BOOST OF DIVERGENT POLEWARD OUTFLOW. AT THE SAME
TIME, THE BULK OF MODEL DATA SUPPORTS A MOISTENING OF THE
CIRCULATION, AND THE COMBINED EFFECTS WILL ALLOW FOR A SHORT PERIOD
OF INTENSIFICATION THROUGH TAU 48. THE SYSTEM IS EXPECTED TO CROSS
THE 26C AROUND TAU 60, AND WILL BEGIN THE WEAKENING STAGE AT THIS
POINT. A STRONG UPPER-LEVEL TROF WILL SLAM INTO THE SYSTEM AROUND
TAU 72, USHERING IN A SEVERE INCREASE IN SHEAR AND DRY AIR,
EFFECTIVELY DECAPITATING THE SYSTEM AND MARKING THE BEGINNING OF
SUBTROPICAL TRANSITION (STT). THE SYSTEM WILL CONTINUE TRACKING
POLEWARD WHILE STEADILY WEAKENING AND COMPLETING STT BY THE END OF
THE FORECAST PERIOD. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT
ON THE OVERALL TRACK SCENARIO, WITH LITTLE IN THE WAY OF CROSS- OR
ALONG-TRACK SPREAD IN THE SHORT-TERM FORECAST PERIOD (48 HOURS).
GFS AND GEFS CONTINUE TO BE THE RIGHTMOST OUTLIERS, TAKING THE
SYSTEM ON A FLATTER TRAJECTORY TO THE EAST THAN THE OTHER MEMBERS
OF THE CONSENSUS, WHICH ARE A CONFINED TO A TIGHTLY PACKED ENVELOPE
THROUGH TAU 48. THE JTWC FORECAST IS POSITIONED NEAR THE CONSENSUS
MEAN WITH HIGH CONFIDENCE IN THE INITIAL 48 HOURS OF THE FORECAST.
IN THE LONGER-RANGE FORECAST, GUIDANCE BEGINS TO DIVERGE
SIGNIFICANTLY. THE NAVGEM, IN LINE WITH ITS KNOWN BIASES, RACES THE
SYSTEM OFF TO THE NORTHEAST SUCH THAT BY TAU 120, IT IS POSITIONED
SOUTHWEST OF ADAK, THE GALWEM FINDS ITSELF NEAR THE KURIL ISLANDS
AND THE GFS IS SITUATED SOUTHEAST OF HONSHU. THE REMAINDER OF THE
GUIDANCE, IN PARTICULAR THE ECWMF, EC-AIFS, AND GEFS, ARE GROUPED
ROUGHLY IN THE MIDDLE BETWEEN THESE OUTLIERS, AND TRACKING AT A
MUCH SLOWER SPEED. OVERALL TRACK SPREAD INCREASES TO 1260NM BY TAU
120. THE JTWC FORECAST IS PLACED ROUGHLY BETWEEN THE ECMWF AND AIFS
TRACKERS WITH LOW CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD
AGREEMENT ON THE INTENSITY TREND WITH A 15-20 KNOT SPREAD IN
POSSIBLE PEAK INTENSITIES BETWEEN 60-80 KNOTS. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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