Advisories

WDPN31 PGTW 231500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 30W (THIRTY) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.9N 166.2E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 162 NM NORTHWEST OF KWAJALEIN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
RAPIDLY CONSOLIDATING TROPICAL DEPRESSION (TD), CHARACTERIZED BY
A FORMATIVE BAND OF DEEP CONVECTION ALONG THE WESTERN SEMICIRCLE 
WRAPPING INTO AN OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC). ALOFT, 
A 200 MB ANTICYCLONIC POINT SOURCE IS ANALYZED IN BOTH AUTOMATED 
ATMOSPHERIC MOTION VECTOR (AMV) DATA AND JTWC SUBJECTIVE UPPER-AIR 
ANALYSIS. ADDITIONALLY, A LATE-SEASON TROPICAL UPPER-TROPOSPHERIC
TROUGH (TUTT) EXTENDS SOUTHWARD TO A POSITION NORTHWEST OF TD 30W,
PLACING THE SYSTEM IN A FAVORABLE DIVERGENT QUADRANT RELATIVE TO THE 
TUTT. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE, AS THE 
LLCC IS OBSCURED BENEATH BLOSSOMING CENTRAL CONVECTION AND LACKS 
RECENT HIGH-RESOLUTION MICROWAVE OR SCATTEROMETER PASSES. THE INITIAL
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON CONCURRENT 
T2.0 (30 KTS) DVORAK CURRENT INTENSITY ESTIMATES FROM PGTW AND PHFO, 
SUPPORTED BY IMPROVED CONVECTIVE ORGANIZATION. ENVIRONMENTAL
CONDITIONS ARE HIGHLY FAVORABLE FOR INTENSIFICATION, CHARACTERIZED BY
MODERATE TO STRONG DUAL-CHANNEL OUTFLOW ENHANCED BY THE OVERHEAD 
POINT SOURCE, LOW VERTICAL WIND SHEAR (VWS), WARM SEA SURFACE 
TEMPERATURES (SSTS), AND HIGH OCEANIC HEAT CONTENT (OHC).

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

CURRENT STEERING MECHANISM: NORTHERN SIDE OF A BELT OF ENHANCED
SOUTHWESTERLIES TO THE SOUTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   PHFO: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TD 30W IS CURRENTLY QUASI-STATIONARY WITH A 
SLIGHT EASTWARD DRIFT IN A WEAK AMBIENT STEERING ENVIRONMENT, 
GOVERNED PRIMARILY BY ENHANCED LOW-LEVEL SOUTHWESTERLIES NEAR THE 
EQUATOR. OVER THE NEXT 24 HOURS, AS THE SYSTEM INTENSIFIES AND THE 
VORTEX DEEPENS, IT WILL COME UNDER THE STEERING INFLUENCE OF
A MID- TO DEEP-LAYER NEAR-EQUATORIAL RIDGE (NER) ANCHORED NEAR THE 
EQUATOR AND TRACK NORTHWARD. BY TAU 36, AN AMPLIFYING MID-LATITUDE 
TROUGH WILL DIG NORTH OF TD 30W WHILE THE NER TO THE EAST 
SIMULTANEOUSLY BUILDS, STEERING THE SYSTEM POLEWARD. BY TAU 72, THE 
MID-LATITUDE TROUGH WILL LIFT NORTHEASTWARD AS AN EXPANSIVE 
SUBTROPICAL RIDGE (STR) BUILDS IN FROM THE WEST AND THE NER 
RETROGRADES WESTWARD SOUTH OF TD 30W. THIS SYNOPTIC EVOLUTION PLACES 
THE SYSTEM WITHIN A COL REGION BETWEEN THE TWO RIDGE COMPLEXES, 
INDUCING QUASI-STATIONARY MOTION BETWEEN TAU 72 AND TAU 96. AFTER TAU 
96, THE STR WILL CONTINUE BUILDING RAPIDLY EASTWARD NORTH OF THE 
VORTEX, DEFLECTING THE SYSTEM WESTWARD BY TAU 120. SIGNIFICANT 
BIFURCATION EXISTS WITHIN THE GLOBAL MODEL SUITE, PARTICULARLY 
BETWEEN THE GFS AND ECMWF, REGARDING THE EVOLUTION OF THE NORTHERN 
STR. THE GFS MAINTAINS A MORE ELONGATED, NORTHEAST-SOUTHWEST ORIENTED 
RIDGE, YIELDING A NORTHEASTWARD RECURVATURE FOR TD 30W. CONVERSELY, 
THE ECMWF AND AI MODELS DEPICT A MORE COMPACT ZONAL RIDGE BUILDING 
EASTWARD, DRIVING TD 30W ONTO A WESTWARD TRAJECTORY BY THE END OF THE 
FORECAST PERIOD. REGARDING INTENSITY, TD 30W RESIDES IN A NEAR-
OPTIMAL ENVIRONMENT. OVER THE NEXT 24 HOURS, THE TUTT TO THE 
NORTHWEST IS EXPECTED TO CUT OFF INTO A DISCRETE TUTT CELL, PLACING 
TD 30W IN A PRIME UPPER-LEVEL DIFFLUENT REGIME AND SUPPORTING NEAR-
RAPID INTENSIFICATION THROUGH TAU 24. RAPID INTENSIFICATION (RI) IS
EXPLICITLY FORECAST FROM TAU 24 TO TAU 48 BEFORE THE TUTT CELL 
PROPAGATES WESTWARD. FROM TAU 72 TO TAU 96, THE BASE OF THE MID-
LATITUDE TROUGH TO THE NORTH WILL ENCROACH UPON TD 30W, INDUCING 
UPPER-LEVEL CONVERGENCE AND TEMPORARILY ARRESTING INTENSIFICATION. 
AFTER TAU 96, TD 30W WILL SEPARATE FROM THE UPPER-LEVEL TROUGH AND 
RESUME STEADY INTENSIFICATION THROUGH TAU 120. 

MODEL DISCUSSION: TRACK GUIDANCE IS HIGHLY UNCERTAIN, EXHIBITING
SIGNIFICANT CROSS- AND ALONG-TRACK SPREAD. THE GUIDANCE SUITE IS 
ROUGHLY SPLIT BETWEEN SOLUTIONS FAVORING A WESTWARD TRAJECTORY AFTER 
TAU 96 AND THOSE DEPICTING NORTHEASTWARD RECURVATURE. MODELS 
SUPPORTING A WESTWARD TRACK INCLUDE ALL AI-BASED MODELS, GALWEM, AND 
ECMWF, WHEREAS GFS, ECEPS, GEFS, JGSM, UKMET, AND MOGREPS FAVOR A
NORTHEASTWARD TRACK. THE AI MODELS ARE TIGHTLY CLUSTERED ALONG A
NORTH-NORTHWESTWARD TRAJECTORY FROM TAU 12 ONWARD AND ANCHOR THE
WESTERN EDGE OF THE GUIDANCE ENVELOPE. THE ECMWF LIES JUST INSIDE THE
AI CLUSTER, WHILE THE JGSM AND GFS MARK THE EASTERN OUTLIERS. THE
JTWC TRACK FORECAST IS POSITIONED NEAR THE DETERMINISTIC ECMWF 
SOLUTION THROUGH THE FORECAST PERIOD WITH LOW CONFIDENCE. INTENSITY 
GUIDANCE IS IN GOOD AGREEMENT ON THE OVERALL INTENSIFICATION TREND. 
HOWEVER, COAMPS-TC (BOTH THE GFS- AND NAVGEM-DRIVEN RUNS) DEPICTS A 
SIGNIFICANTLY WEAKER SYSTEM, CAPPING INTENSITY BELOW 75 KTS THROUGH 
TAU 120. HAFS-A AND HWRF PEAK THE SYSTEM AROUND TAU 72 AT 115 KTS 
BEFORE WEAKENING IT; HOWEVER, BOTH TRACK AMONG THE EASTERNMOST 
OUTLIERS, PLACING TD 30W IN A LESS FAVORABLE POSITION RELATIVE TO THE 
TUTT CELL AND CLOSER TO THE ENCROACHING MID-LATITUDE TROUGH AROUND 
TAU 72. THE JTWC INTENSITY FORECAST CLOSELY TRACKS THE GOOGLE 
DEEPMIND (GDM) SOLUTION THROUGH THE FORECAST PERIOD. 

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