Advisories

WDPN32 PGTW 300300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 26W (TWENTYSIX) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.6N 151.9E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 422 NM EAST-NORTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION (TD) 26W WITH AN ELONGATED LOW-LEVEL CIRCULATION CENTER
(LLCC) AND PERSISTENT, DEEP CONVECTION WRAPPING ALONG THE WESTERN
AND SOUTHERN PERIPHERY. THE SYSTEM HAS STEADILY BECOME BETTER
DEFINED DURING THE PAST DAY, WITH THE MID-LEVEL CIRCULATION
BECOMING LESS TILTED RELATIVE TO THE LLCC. A 292149Z GMI PASS
REVEALED A CONSOLIDATING LOW-LEVEL STRUCTURE, WITH RAINBANDS
WRAPPING INTO THE DEVELOPING CORE. THE ENVIRONMENT APPEARS TO BE
FAVORABLE FOR FURTHER DEVELOPMENT, CHARACTERIZED BY VERY WARM SEA
SURFACE TEMPERATURES (SST) OF 29-30 DEGREES CELSIUS AND VERY HIGH
OCEAN HEAT CONTENT (OHC) OF 120-140 KJ PER CM2, ABUNDANT DEEP-LAYER
MOISTURE, AND LOW TO MODERATE WESTERLY VERTICAL WIND SHEAR (VWS).
THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON A
COMBINATION OF THE CURVED BANDING IN THE MSI AND THE NASCENT CORE
STRUCTURE IN THE GMI DATA. THE INITIAL INTENSITY HAS BEEN SET AT 25
KTS WITH MEDIUM CONFIDENCE, SUPPORTED BY THE T1.5 CLASSIFICATION
FROM PGTW AND THE IMPROVING CONVECTIVE STRUCTURE.

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

CURRENT STEERING MECHANISM: SOUTHERN FLANK OF A LOWER-LEVEL
SUBTROPICAL RIDGE (STR) TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   CIMSS D-PRINT: 33 KTS AT 300000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TD 26W WILL TRACK WEST-NORTHWESTWARD ALONG THE
SOUTHERN PERIPHERY OF THE STR THROUGH TAU 48. AROUND TAU 48, TS 25W
WILL MERGE INTO A PROGRESSIVE TROUGH EAST OF HOKKAIDO, WHICH WILL
ERODE THE STR. THIS EVOLUTION WILL RESULT IN A MARKED WEAKENING OF
THE PRIMARY STEERING INFLUENCE. FROM TAU 36 TO TAU 48, THE FORECAST
BRINGS THE GALE-FORCE WIND RADII TO SAIPAN AND TINIAN. THE SYSTEM'S
FORWARD MOTION WILL DECREASE FROM 7-9 KTS TO 2-3 KTS BETWEEN TAU 48
AND TAU 60. AFTER TAU 60, THE DEEP-LAYER RIDGE WILL REBUILD AND
STEER THE SYSTEM POLEWARD. FOR THE FIRST FOUR DAYS, TD 26W WILL
MOVE THROUGH A FAVORABLE ENVIRONMENT OF LOW VWS, VERY WARM SST AND
VERY HIGH OHC, AND RICH DEEP-LAYER MOISTURE. INITIAL
INTENSIFICATION WILL BE SLOW DUE TO THE SYSTEM'S ELONGATED AND
DISORGANIZED STRUCTURE. ONCE AN INNER CORE BECOMES ESTABLISHED,
STEADY TO RAPID INTENSIFICATION IS LIKELY. OHC NEAR 150 KJ PER CM2
AS THE SYSTEM REACHES ITS LOWEST FORWARD SPEED WILL MITIGATE THE
DETRIMENTAL EFFECTS OF UPWELLING. BETWEEN TAU 96 AND TAU 120,
INCREASING SHEAR AND LOWER OHC WILL LIMIT FURTHER INTENSIFICATION.

MODEL DISCUSSION: SIGNIFICANT DISAGREEMENT EXISTS AMONG THE TRACK
GUIDANCE, PARTICULARLY REGARDING THE TIMING OF THE POLEWARD TURN,
DUE TO UNCERTAINTY IN THE EVOLUTION OF THE PROGRESSIVE TROUGH AS IT
INTERACTS WITH TS 25W. NAVGEM, THE UKMET ENSEMBLE MEAN, AND GALWEM
ARE THE SOONEST TO RECURVE THE SYSTEM, WHILE THE AI MODELS DELAY
THE POLEWARD TURN BY 24-36 HOURS. GFS TRACKS THE CIRCULATION
FURTHEST WEST AND KEEPS IT QUASI-STATIONARY THROUGH TAU 120. AS A
RESULT, THE JTWC CONSENSUS (CONW) DEPICTS THE POLEWARD TURN ABOUT
150 NM EAST OF THE AI CONSENSUS. THE JTWC FORECAST TRACK IS PLACED
WITH LOW CONFIDENCE, CLOSEST TO BUT SLIGHTLY EAST OF THE AI
CONSENSUS. THE LARGE TRACK SPREAD RESULTS IN SUBSTANTIAL
DIFFERENCES IN THE TIMING AND MAGNITUDE OF INTENSIFICATION AMONG
THE INTENSITY AIDS. NEARLY ALL INTENSITY GUIDANCE INDICATES
SIGNIFICANT INTENSIFICATION, WITH GFS PEAKING AT 110 KTS AND
DEEPMIND PEAKING NEAR 125 KTS. THE SHIPS RAPID INTENSIFICATION
INDEX ESTIMATES A 61 PERCENT CHANCE OF A 65-KT INCREASE IN THE NEXT
72 HOURS. THE JTWC INTENSITY FORECAST IS SET ON THE HIGH END OF THE
GUIDANCE ENVELOPE, WITH THE TIMING OF INTENSIFICATION ALIGNED WITH
DEEPMIND.

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