Advisories

WDPN32 PGTW 141500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 29W (TWENTYNINE) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.6N 161.2E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 989 NM EAST-SOUTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) EXHIBITING
WEAK, TRANSIENT CONVECTIVE BURSTS PROXIMATE TO THE ASSESSED CENTER,
WHICH RAPIDLY SHEAR AND DISSIPATE WESTWARD. OVER THE PAST 12 HOURS,
THE LLCC EXECUTED A COUNTER-CLOCKWISE LOOP AFTER DECOUPLING FROM A
MID-LEVEL CONVECTIVE MESOVORTEX. THE REMNANT DEEP CONVECTION PERSISTS 
BUT IS DISPLACED APPROXIMATELY 100 NM WEST OF THE LLCC. A 141024Z 
ASCAT-B PASS REVEALED THAT THE WIND FIELD REMAINS STRUCTURALLY
ASYMMETRIC, ALTHOUGH SIGNIFICANTLY MORE COMPACT COMPARED TO 24 HOURS 
AGO. THE CIRCULATION IS POORLY DEFINED TO THE NORTH-NORTHWEST; 
HOWEVER, A SWATH OF 25-30 KNOT WINDS IS EVIDENT ACROSS THE SOUTHERN 
SEMICIRCLE, WITH 20-25 KNOT WINDS BEGINNING TO WRAP ALONG THE EASTERN 
FLANK. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON 
THE EXPOSED LLCC RESOLVED IN EIR. THE INITIAL INTENSITY IS ASSESSED 
WITH HIGH CONFIDENCE, SUPPORTED BY THE CONCURRENT ASCAT DATA. 
ENVIRONMENTAL CONDITIONS ARE GENERALLY FAVORABLE; SSTS ARE VERY WARM,
OCEAN HEAT CONTENT (OHC) IS SUFFICIENT TO SUPPORT INTENSIFICATION, 
DEEP-LAYER VERTICAL WIND SHEAR (VWS) IS LOW (ALTHOUGH MID-LEVEL SHEAR
IS ESTIMATED TO BE STRONGER), AND UPPER-LEVEL OUTFLOW IS MODESTLY 
FAVORABLE, PROVIDING STEADY WESTWARD OUTFLOW.

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

CURRENT STEERING MECHANISM: SOUTHERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED FAR TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG WESTWARD
   OTHER FACTORS: MODERATE TO STRONG MID-LEVEL EASTERLY SHEAR. DRY
MID-LEVEL AIR TO THE NORTHEAST. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 29W IS FORECAST TO CONTINUE ITS
COUNTER-CLOCKWISE LOOPING MOTION OVER THE NEXT 12 HOURS, BEFORE
ESTABLISHING A WEST-NORTHWESTWARD HEADING. BY TAU 24, THE TRAJECTORY
WILL BECOME LOCKED, AND 29W WILL TRACK ON A STEADY 280-285 DEGREE 
HEADING ALONG THE EQUATORWARD PERIPHERY OF THE EXPANSIVE STR CENTERED 
TO THE NORTH. TRACK SPEEDS WILL BE SLOW IN THE EARLY PORTION OF THE 
FORECAST AS THE SYSTEM COMPLETES ITS LOOP. BY TAU 24, 29W WILL 
ACCELERATE TO 13 KNOTS AND MAINTAIN THAT TRANSLATION SPEED THROUGH AT 
LEAST TAU 96, BEFORE DECELERATING SLIGHTLY BY THE END OF THE FORECAST 
PERIOD. THE KEY QUESTION WITH THIS FORECAST IS THE INTENSITY; 
SPECIFICALLY, THE POTENTIAL FOR RAPID INTENSIFICATION (RI) AND THE 
TIMING OF THIS EVENT RELATIVE TO THE MARIANAS ISLANDS. IN THE SHORT-
TERM, THE SYSTEM IS UNLIKELY TO INTENSIFY SIGNIFICANTLY DUE TO 
PERSISTENT MODERATE NORTHEASTERLY SHEAR AND THE PRESENCE OF DRY MID-
LEVEL AIR TO THE NORTHEAST. FOR THESE REASONS, THE FORECAST CALLS FOR 
ONLY 10 KNOTS OF INTENSIFICATION OVER THE NEXT 24 HOURS. CONDITIONS 
IMPROVE MARKEDLY NEAR TAU 36, WHEN THE DRY AIR IS MIXED OUT, VWS 
RELAXES, AND ALL NUMERICAL GUIDANCE POINTS TO THE SYSTEM ATTAINING A 
VERTICALLY ALIGNED, SYMMETRICAL VORTEX. ASSUMING 29W ACHIEVES
SYMMETRIZATION BY TAU 48, THE FORECAST SPECIFICALLY CALLS FOR RI
BETWEEN TAU 48 AND TAU 72, AND ANOTHER ROUND OF RI FROM TAU 72 TO
TAU 96, AS THE SYSTEM APPROACHES AND PASSES THROUGH THE MARIANAS
ISLAND CHAIN. 29W IS EXPECTED TO CONTINUE INTENSIFYING, ALBEIT AT A
SLOWER RATE, THROUGH TAU 120, REACHING A PEAK OF AT LEAST 125 KNOTS
BY THE END OF THE FORECAST. SOME OF THE MORE AGGRESSIVE MODELS SHOW
THE SYSTEM ACHIEVING VORTEX SYMMETRIZATION AND STARTING RI EARLIER,
RESULTING IN A SYSTEM THAT IS APPROACHING SUPER TYPHOON STRENGTH AS
IT REACHES CPA TO GUAM. GIVEN THE EXTENSIVE CORE CONSTRUCTION
REQUIRED, THIS OUTCOME REMAINS A HIGHER-END SCENARIO AT THIS TIME.  

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
OVERALL GOOD AGREEMENT, DEPICTING A WEST-NORTHWESTWARD TRACK THROUGH 
THE ENTIRE FORECAST PERIOD, THOUGH THERE IS A MODEST AMOUNT OF 
UNCERTAINTY BEING INTRODUCED INTO THE LONG-RANGE FORECAST POINTS
AFTER TAU 72. CROSS-TRACK SPREAD IN THE JTWC CONSENSUS IS 130 NM,
BETWEEN NAVGEM (NVGM) AND JGSM ON THE NORTHERN EDGE, AND THE TIGHTLY
CLUSTERED AI CONSENSUS, GOOGLE DEEPMIND, AND THE OTHER AI MODELS ON
THE SOUTHERN FLANK. ALONG-TRACK SPREAD IS THE PREVALENT UNCERTAINTY 
DRIVER, AS THE AI SUITES SYSTEMATICALLY OUTPACE THE DYNAMICAL AND 
ENSEMBLE MEMBERS (PARTICULARLY GEFS MEAN AND JGSM, WHICH LAG THE AI 
MEAN BY 200 NM AT TAU 72). BY TAU 120, CROSS-TRACK SPREAD INCREASES 
TO APPROXIMATELY 210 NM BETWEEN THE AI GROUPING ON THE SOUTHERN EDGE 
AND NAVGEM/GEFS ON THE NORTHERN PERIPHERY. ALONG-TRACK SPEED ERROR AT 
DAY 5 EXPANDS TO 380 NM. ENSEMBLE GUIDANCE IS IN STRONG AGREEMENT 
OVERALL, WITH ONLY THE GEFS DEPICTING A MEAN TRACK NORTH OF SAIPAN. 
THE REMAINDER OF THE SUITE (ECEPS, CMC, ICON, UKMET, AIFS, AND 
DEEPMIND) ALL COINCIDE ON A DIRECT IMPACT TO GUAM OR PASS THROUGH THE 
GUAM-ROTA CHANNEL. THE EXPERIMENTAL SUPER ENSEMBLE IS POSITIONED JUST 
NORTH OF GUAM, EXHIBITING SOLID RUN-TO-RUN STABILITY OVER THE PAST 24 
HOURS. THE JTWC FORECAST TRACK STRONGLY FAVORS THE AI CONSENSUS 
(AICN) MEAN THROUGH THE PROJECTION ENVELOPE WITH HIGH CONFIDENCE. 
INTENSITY GUIDANCE CONCURS ON THE GENERAL INTENSIFICATION TREND, BUT 
EXHIBITS PRONOUNCED DISPERSION REGARDING PEAK INTENSITY AND THE RI 
INITIATION TIMELINE AFTER TAU 48. BY TAU 48, THE STATISTICAL SHIPS 
GUIDANCE (NVGM AND GFS) DIVERGES FROM THE MESOSCALE AND AI MODELS, 
DEPICTING A MUCH SLOWER RATE OF INTENSIFICATION AND A PEAK OF ONLY 
70-85 KNOTS BY TAU 120. THE COAMPS-TC (BOTH NVGM AND GFS) INITIATES 
RI AT TAU 48, ATTAINING PEAK INTENSITIES OF 120-125 KNOTS BY TAU 120. 
THE HAFS-A AND DEEPMIND ARE THE MOST AGGRESSIVE MODELS, PROJECTING RI 
ONSET NEAR TAU 36 AND PEAK AT 130-135 KNOTS BY TAU 96. COAMPS-TC RI 
PROBABILITIES EXCEED 80 PERCENT IN THE 48-72 HOUR AND 72-108 HOUR 
WINDOWS, WHILE DEEPMIND INDICATES NEAR 100 PERCENT PROBABILITIES. THE 
JTWC INTENSITY FORECAST IS PLACED CLOSE TO CTCX GUIDANCE THROUGH THE 
PERIOD, WITH MEDIUM CONFIDENCE THROUGH TAU 72 AND LOW CONFIDENCE 
THEREAFTER.    

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