Advisories

WDPN32 PGTW 030900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 26W (CHOI-WAN) WARNING NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.4N 145.9E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 252 NM NORTH OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON 26W
(CHOI-WAN) WITH A CLOUD-FILLED EYE AND A MORE DISORGANIZED
CONVECTIVE STRUCTURE COMPARED TO 6 HOURS AGO. THE MSI ALSO SHOWS
SOME DRY AIR BEING PULLED INTO THE CORE OF 26W ALONG THE WESTERN
PERIPHERY, WHICH COULD BE THE CAUSE FOR THE HALTED DEVELOPMENT. A
030228Z AMSR3 37 GHZ MICROWAVE IMAGE REVEALED AN ELLIPTIC MICROWAVE
EYE FEATURE WITH A SLIGHT WEAKNESS IN THE WESTERN SEMICIRCLE. THE
89 GHZ VERSION OF THE SAME PASS SHOWED THE STRONGEST CONVECTION
CONFINED TO THE SOUTHEASTERN QUADRANT OF THE SYSTEM. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE ANIMATED MSI
AND EXTRAPOLATION FROM THE AMSR3 MICROWAVE IMAGE SUITE. THE INITIAL
INTENSITY OF 80 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A
COMBINATION OF THE AGENCY DVORAK FIXES OF T5.0 AND THE LOWER CIMSS
INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE FROM THE 022345Z METOP-B
ASCAT PASS WITH MINOR ADJUSTMENTS BASED ON THE OBJECTIVE BEST TRACK

CURRENT STEERING MECHANISM: THE WESTERN EXTENSION OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T5.0 - 90 KTS
   CIMSS SATCON: 77 KTS AT 030600Z
   CIMSS ADT: 59 KTS AT 030600Z
   CIMSS AIDT: 63 KTS AT 030600Z
   CIMSS D-PRINT: 76 KTS AT 030600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: SLIGHT DRY AIR ENTRAINMENT ALONG THE WESTERN
PERIPHERY

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: THE STEERING MECHANISM FOR 26W HAS SHIFTED
FROM THE NEAR EQUATORIAL RIDGE TO THE SUBTROPICAL RIDGE TO THE
NORTHEAST. THIS HAS CAUSED THE TRAJECTORY TO BECOME SLIGHTLY
MORE NORTHWARD OVER PAST 6 HOURS. 26W IS FORECAST TO TURN FURTHER 
NORTHWARD AS IT TRACKS ALONG THE WESTERN PERIPHERY OF THE STR
THROUGH TAU 72. AFTER TAU 72, THE SYSTEM WILL ACCELERATE
NORTHEASTWARD AS IT ROUNDS THE RIDGE AXIS AND BEGINS TO INTERACT
WITH THE STRONG UPPER-LEVEL FLOW. EXTRATROPICAL TRANSITION IS
EXPECTED TO BE COMPLETE AROUND TAU 96, SOUTH OF THE KAMCHATKA
PENINSULA, ONCE THE SYSTEM BECOMES EMBEDDED UNDERNEATH THE JET. IN
TERMS OF INTENSITY, 26W IS FORECAST TO INTENSIFY OVER THE NEXT 24
HOURS TO A PEAK INTENSITY OF AROUND 105 KTS AS THE ENVIRONMENT
REMAINS FAVORABLE WITH LOW SHEAR, VERY WARM SST, AND ROBUST
OUTFLOW. THE PRIMARY LIMITING FACTOR WILL BE THE DRY AIR TO THE
WEST. AROUND TAU 36, OCEAN HEAT CONTENT WILL START TO DROP AND
EQUATORWARD OUTFLOW WILL BECOME RESTRICTED, CAUSING 26W TO WEAKEN
THROUGH TAU 72. FOLLOWING TAU 72, THE SYSTEM WILL TAP INTO AN
EXTREME POLEWARD OUTFLOW CHANNEL, SUPPORTED BY A VERY STRONG JET
MAX TO THE NORTH. THIS WILL OFFSET THE COOL SST AND HIGH
SOUTHWESTERLY VERTICAL WIND SHEAR, ALLOWING FOR 26W TO LIKELY
MAINTAIN TYPHOON INTENSITY THROUGH THE INITIAL STAGES OF
FRONTOGENESIS.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN MODERATE AGREEMENT
THROUGH TAU 72 WITH MOST OF THE UNCERTAINTY REVOLVING AROUND THE
SPEED OF ADVANCE AROUND THE RIDGE. WHILE CROSS-TRACK SPREAD IS ONLY
AROUND 100 NM AT TAU 72, ALONG-TRACK SPREAD IS ABOUT 250 NM. GFS
AND NAVGEM ARE THE SLOWEST TRACKERS WHILE EC-AIFS AND THE GOOGLE
DEEPMIND ARE THE FASTEST. AT TAU 96, THE ALONG-TRACK SPREAD
SIGNIFICANTLY INCREASES TO OVER 600 NM. THE JTWC TRACK FORECAST IS
PLACED SLIGHTLY FASTER THAN THE CONSENSUS THROUGH TAU 72 WITH
MEDIUM CONFIDENCE. THE JTWC FORECAST THEN HEDGES CLOSER TO THE
GOOGLE DEEPMIND ENSEMBLE MEAN THROUGH TAU 96 WITH LOW CONFIDENCE.
INTENSITY GUIDANCE GENERALLY AGREES ON INTENSIFICATION THROUGH TAU
24-36 FOLLOWED BY STEADY WEAKENING. MULTIPLE RAPID INTENSIFICATION
(RI) AIDS HAVE TRIGGERED THIS MODEL RUN, AND SUGGEST A PEAK
INTENSITY OF 115-125 KTS. THE MESOSCALE MODELS ON THE OTHER HAND,
SHOW A PEAK CLOSER TO 95-105 KTS. AS A RESULT, THE JTWC INTENSITY
FORECAST IS PLACED ON THE HIGH END OF THE MESOSCALE GUIDANCE
THROUGH TAU 36 AND THEN NEAR THE CONSENSUS THROUGH TAU 96 WITH
OVERALL 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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