WDPN31 PGTW 270900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W (JANGMI) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.6N 137.5E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 36 NM WEST OF YAP
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD
LOW-LEVEL CIRCULATION (LLC) POSITIONED JUST WEST OF YAP. DEEP 
CONVECTION IS DEVELOPING ACROSS THE WESTERN AND SOUTHERN FLANKS OF 
THE CIRCULATION BUT REMAINS DISORGANIZED AND HAS YET TO DEVELOP INTO 
DISCRETE BANDING FEATURES. EARLIER SCATTEROMETER DATA DEPICTED A VERY 
BROAD REGION OF MINIMUM WINDS, WHICH ENCOMPASSED YAP, AS REFLECTED IN 
THE YAP SURFACE OBSERVATIONS, WHICH HAVE REMAINED GENERALLY LIGHT AND
VARIABLE OVER THE PAST 12 HOURS. PRESSURE READINGS AT YAP SHOW
STEADY PRESSURE FALLS OVER THE PAST 12 HOURS, BUT THE MOST RECENT
OBSERVATIONS INDICATE PRESSURES STABILIZING AT AROUND 1004MB. THE 
BROAD NATURE OF THE WIND MINIMA MAKES DEFINING A DISCRETE LOW LEVEL
CIRCULATION CENTER (LLCC) CHALLENGING; THEREFORE, THE INITIAL 
POSITION IS ASSESSED WITH LOW CONFIDENCE. THE INITIAL INTENSITY IS 
ASSESSED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF SUBJECTIVE DVORAK
CURRENT INTENSITY ESTIMATES, SUPPORTED BY PRIOR SCATTEROMETER
DATA INDICATING MAXIMUM WINDS IN THE 25 KNOT RANGE, PRIMARILY
CONFINED TO THE SOUTH-SOUTHEASTERN QUADRANT. ENVIRONMENTAL
CONDITIONS ARE FAVORABLE FOR INTENSIFICATION, CHARACTERIZED BY LOW 
DEEP-LAYER VERTICAL WIND SHEAR (VWS), WARM SEA SURFACE TEMPERATURES 
(SSTS), AND MODERATE POLEWARD AND EQUATORWARD OUTFLOW ALOFT. THE
0000Z YAP SOUNDING INDICATES A FULLY SATURATED ATMOSPHERE THROUGH
200MB, LIGHT WESTERLIES THROUGH 500MB, AND 15-20 KNOT EASTERLIES UP 
TO 200MB.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: WESTERN FLANK OF A WEAK, LOW TO
MID-LEVEL RIDGE POSITIONED SOUTH OF GUAM. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.0 - 25 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T1.0 - 25 KTS
   CIMSS D-PRINT: 23 KTS AT 270600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: VORTEX ASYMMETRY AND BROAD NATURE OF THE LOW
LEVEL CIRCULATION. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 06W (JANGMI) IS
DRIFTING NORTH-NORTHWESTWARD ALONG THE WESTERN FLANK OF A SHALLOW,
MESOSCALE RIDGE POSITIONED SOUTH OF GUAM. OVER THE NEXT 24 HOURS,
AS TD 06W STEADILY INTENSIFIES, THE SUBTROPICAL RIDGE (STR) TO THE 
EAST IS FORECAST TO BUILD AND EXTEND NORTHWARD OVER THE MARIANAS 
CHAIN. FROM TAU 36, THE RIDGE TO THE EAST CONTINUES TO BUILD AND 
REORIENTS TO A NORTHWEST-SOUTHEAST AXIS, WHILE THE STR OVER EASTERN 
CHINA RECEDES WESTWARD, ALLOWING TD 06W TO TRACE A NORTHWESTWARD 
TRACK THROUGH TAU 72. BY TAU 72, THE STR TO THE EAST BEGINS A SLOW 
PROGRESSION EASTWARD, WHILE THE STR OVER CHINA CONTINUES TO DRIFT 
WESTWARD, OPENING UP A WEAKNESS OR COL REGION IN THE RIDGE PATTERN, 
CENTERED IN THE VICINITY OF OKINAWA. AFTER TAU 72, TD 06W WILL BEGIN 
A SLOW RECURVATURE AROUND THE STR TO THE EAST AND TOWARDS THE COL 
REGION DESCRIBED ABOVE. THE SYSTEM IS FORECAST TO REACH THE RIDGE 
AXIS AT TAU 120, SLOWING SLIGHTLY AS IT APPROACHES THE AXIS. 
REGARDING INTENSITY, DUE TO THE BROAD NATURE OF THE CIRCULATION AND 
THE LACK OF A VERTICALLY ALIGNED VORTEX, TD 06W WILL BE SLOW TO 
INTENSIFY FOR THE FIRST 24 HOURS OF THE FORECAST, INTENSIFYING AT THE 
CLIMATOLOGICAL RATE OF ONE T-NUMBER PER DAY. THE MAJORITY OF THE 
MESOSCALE GUIDANCE SUGGESTS TD 06W WILL ACHIEVE VORTEX ALIGNMENT 
AROUND TAU 24, WHILE SIMULTANEOUSLY TRACKING OVER EXTREMELY WARM 
WATERS WITH HIGH OCEAN HEAT CONTENT (OHC) AND EXPERIENCING AN 
INCREASE IN UPPER-LEVEL OUTFLOW. THIS COMBINATION OF FACTORS WILL 
ENABLE THE SYSTEM TO INTENSIFY AT A NEAR-RAPID RATE FROM TAU 24 TO 
TAU 48, AND A PERIOD OF RAPID INTENSIFICATION (RI) IS EXPLICITLY 
FORECAST BETWEEN TAU 48 AND TAU 72. THE PEAK INTENSITY OF AT LEAST 90 
KNOTS IS FORECAST TO OCCUR AT TAU 96. AFTER TAU 96, THE SYSTEM WILL 
MOVE OVER A TONGUE OF COOL (LESS THAN 26 C) WATERS 
PRESENT EAST OF OKINAWA. COMBINED WITH AN UPTICK IN DEEP-LAYER 
VERTICAL WIND SHEAR, THE RESULT WILL BE A STEADY WEAKENING OF TD 06W 
THROUGH THE REMAINDER OF THE FORECAST PERIOD.

MODEL DISCUSSION: DETERMINISTIC, ENSEMBLE, AND ARTIFICIAL
INTELLIGENCE (AI) TRACK GUIDANCE ARE IN GOOD AGREEMENT ON THE OVERALL 
TRACK SCENARIO. THE CONSENSUS PACKAGE DEPICTS THREE GROUPINGS OF 
MODELS; A WESTERN GROUP COMPRISING THE GALWEM AND UKMET ENSEMBLE MEAN 
IS POSITIONED WELL WEST (165 NM) OF THE MAIN GROUP, TRACKING THE 
SYSTEM TOWARDS ISHIGAKIJIMA. THE MAIN GROUPING CONSISTS OF THE ECMWF, 
ECEPS, GFS, GEFS, MULTIPLE AI MODELS, AND THE CONSENSUS MEAN. AN 
EASTERN GROUP CONSISTS OF THE JGSM, JENS, AND THE GOOGLEDEEP MIND 
EXPERIMENTAL AI MODEL, LOCATED ABOUT 100NM EAST OF THE MAIN GROUP. 
CROSS-TRACK SPREAD BETWEEN THE TWO OUTLIER GROUPS IS 205NM AT TAU 72, 
INCREASING TO 430NM AT TAU 120. HOWEVER, THE INTERIOR CORE GROUP IS 
MUCH MORE TIGHTLY PACKED, WITH A CROSS-TRACK SPREAD OF 50NM AT TAU 72 
AND 90NM AT TAU 120. THE JTWC FORECAST IS PLACED JUST EAST OF THE 
CONSENSUS MEAN, HEDGED SLIGHTLY TOWARDS THE GFS TRACK, WHICH IS ON 
THE EASTERN EDGE OF THE CORE GROUP ENVELOPE. CONFIDENCE IS HIGH 
THROUGH TAU 72 AND MEDIUM THEREAFTER. THE JTWC TRACK FORECAST IS ALSO 
CONSISTENT WITH THE EXPERIMENTAL MULTI-MODEL SUPER-ENSEMBLE MEAN 
THROUGH THE FORECAST PERIOD. INTENSITY GUIDANCE IS ALSO IN OVERALL 
AGREEMENT, WITH A SLOW BUT STEADY INTENSIFICATION TREND INITIALLY, 
FOLLOWED BY A PERIOD OF FASTER INTENSIFICATION AFTER TAU 36. HOWEVER, 
THERE IS A 30-KNOT RANGE IN THE PEAK INTENSITY BETWEEN HAFS-A ON THE 
LOW SIDE (65 KTS) AND HWRF, CTCX, AND THE GOOGLEDEEP MIND AI MODEL 
ON THE UPPER END (95 KTS), WHILE THE REMAINDER OF THE GUIDANCE LIES
BETWEEN THOSE VALUES. THE JTWC FORECAST IS PLACED NEAR THE SHIPS
(GFS) THROUGH TAU 24, THEN CLOSELY TRACES THE HWRF, CTCX, AND AI
TRACKERS THEREAFTER.  

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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