Advisories

WDPN31 PGTW 152100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 24W (TWENTYFOUR) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.8N 148.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 176 NM EAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION 24W MOVING VERY SLOWLY WITH A FULLY OBSCURED LOW-LEVEL
CIRCULATION CENTER (LLCC) THAT IS NOW TUCKED UNDERNEATH THE
NORTHEASTERN PORTION OF DEEP CONVECTION. THE OVERALL CIRCULATION
REMAINS QUITE BROAD AND ELONGATED IN THE SOUTHWEST-NORTHEAST AXIS.
A 151528Z GMI 89 GHZ MICROWAVE IMAGE REVEALED CURVED CONVECTIVE
BANDING CONFINED TO THE SOUTHWESTERN QUADRANT WHILE THE 37 GHZ
VERSION OF THE SAME PASS SHOWED A WEAK LOW EMISSIVITY REGION NEAR
THE ASSESSED CENTER. THE INITIAL POSITION IS PLACED WITH LOW
CONFIDENCE BASED ON THE ANIMATED EIR IMAGERY AND THE GMI PASS DUE
TO THE BROAD NATURE OF THE CIRCULATION. THE INITIAL INTENSITY OF 30
KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE HIGH END OF THE
AGENCY DVORAK AND CIMSS INTENSITY ESTIMATES LISTED BELOW. 
ENVIRONMENTAL ANALYSIS INDICATES THAT 24W IS IN A MARGINALLY
FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE OUTFLOW ALOFT, LOW
(5-10 KTS) VERTICAL WIND SHEAR, DRY AIR ENTRAINMENT FROM THE NORTH,
AND WARM (29-30 C) SEA SURFACE TEMPERATURES.

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

CURRENT STEERING MECHANISM: WEAK STEERING PATTERN WITH RIDGING TO
BOTH THE NORTH AND EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T1.5 - 25 KTS
   CIMSS SATCON: 28 KTS AT 151800Z
   CIMSS ADT: 29 KTS AT 151800Z
   CIMSS AIDT: 26 KTS AT 151800Z
   CIMSS D-MINT: 29 KTS AT 151617Z
   CIMSS D-PRINT: 28 KTS AT 151800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: DRY AIR TO THE NORTH

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS FORECAST IS FURTHER EAST AND
TRACKS POLEWARD MORE QUICKLY AFTER TAU 72 COMPARED TO THE PREVIOUS
FORECAST.

FORECAST DISCUSSION: 24W IS FORECAST TO BEGIN TRACKING NORTHWARD 
WITHIN THE NEXT 6-12 HOURS AS AN INCOMING SHORTWAVE TROUGH PROPAGATES 
EASTWARD AND BREAKS DOWN THE WESTERN PERIPHERY OF THE SUBTROPICAL 
RIDGE (STR) THAT IS CURRENTLY CENTERED TO THE NORTH-NORTHEAST OF 24W. 
A GENERALLY NORTHWARD TRACK IS THEN FORECAST TO PERSIST THROUGH TAU 
24, PRIMARILY DRIVEN BY THE NORTHERN EXTENSION OF A NEAR EQUATORIAL 
RIDGE POSITIONED TO THE SOUTHEAST. NEAR TAU 24, THE SYSTEM WILL BEGIN 
TO INTERACT WITH THE SOUTHWESTERN PERIPHERY OF THE STR, WHICH WILL 
DIRECT THE VORTEX NORTHWESTWARD THROUGH TAU 96. AFTER TAU 96, 24W IS 
EXPECTED TO ROUND THE WESTERN EXTENT OF THE STR AND BEGIN TO 
ACCELERATE NORTHEASTWARD. 24W IS CURRENTLY FORECAST TO STAY EAST OF 
HONSHU, HOWEVER, THERE IS STILL SOME UNCERTAINTY IN THE TIMING AND 
TRAJECTORY OF THE NORTHEASTWARD TURN AFTER TAU 96. IF 24W STAYS ON A 
NORTHWESTWARD TRACK FOR LONGER THAN ANTICIPATED, IT COULD SKIRT THE 
COAST AND IMPACT AREAS NEAR THE KANTO PLAIN. IN TERMS OF INTENSITY, 
24W IS FORECAST TO STEADILY INTENSIFY THROUGH TAU 60 AS THE VORTEX 
CONSOLIDATES AND POLEWARD OUTFLOW GREATLY IMPROVES. AFTER TAU 60, THE 
SYSTEM WILL BATTLE WITH DRY AIR ENTRAINMENT FROM THE WEST, CAUSING THE 
SYSTEM TO HALT THE INTENSIFICATION TREND. IF 24W IS ABLE TO 
CONSOLIDATE AND FORM A MORE SYMMETRIC CORE, THEN FURTHER 
NTENSIFICATION COULD BE POSSIBLE AS SHEAR IS EXPECTED TO REMAIN 
RELATIVELY LOW. AFTER TAU 96, FURTHER INTENSIFICATION IS ALSO POSSIBLE 
DUE TO THE SYSTEM TAPPING INTO A ROBUST POLEWARD OUTFLOW CHANNEL 
PROVIDED BY A STRONG JET STREAK OVER NORTHERN JAPAN. NOTABLY, THE 
HAFS-A MODEL SHOWS THE SYSTEM STRUGGLING TO CONSOLIDATE AND IS 
THEREFORE NEVER ABLE TO FULLY STAVE OFF THE DRY AIR. AS IT STANDS, 
24W IS FORECAST TO MAINTAIN LOW TYPHOON-STRENGTH THROUGH THE 
REMAINDER OF THE FORECAST PERIOD.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH 
TAU 72 WITH THE EXCEPTIONS OF JGSM AND NAVGEM, WHICH ARE MUCH FURTHER 
EQUATORWARD THAN THE REMAINDER OF GUIDANCE. DISCOUNTING THE TWO 
OUTLIERS, THE CROSS-TRACK SPREAD AT TAU 72 IS MEASURED TO BE ABOUT 
150 NM. AFTER TAU 72, MODELS BEGIN TO DIVERGE DUE TO DIFFERENCES IN 
THE TIMING AND SPEED OF THE TRACK AROUND THE RIDGE AXIS. THE 
EXPERIMENTAL GOOGLE DEEPMIND ENSEMBLE MEAN AND EC-AIFS ARE THE 
FURTHEST EAST AND QUICKER AROUND THE RIDGE WHILE THE DETERMINISTIC GFS 
AND ECMWF TRACKERS ARE WESTWARD AND SLOWER. THE JTWC TRACK FORECAST IS 
PLACED NEAR THE MODIFIED CONSENSUS THROUGH TAU 72 AND THEN CLOSER TO 
THE AI-BASED MODELS DUE TO THEIR STRONG PERFORMANCE IN THE RECURVING 
TRACK TYPE. INTENSITY GUIDANCE GENERALLY AGREES ON INTENSIFICATION 
THROUGH TAU 60 FOLLOWED BY A STEADY INTENSITY THROUGH TAU 120. 
INTERESTINGLY, GOOGLE DEEPMIND IS AMONG THE MOST AGGRESSIVE MODELS, 
DEPICTING A PEAK INTENSITY OF AROUND 80 KTS AT TAU 72. THE JTWC 
INTENSITY FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS THROUGHOUT 
THE FORECAST PERIOD WITH MEDIUM CONFIDENCE.

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