Advisories

WDPN32 PGTW 030300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 26W (CHOI-WAN) WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.6N 145.3E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 206 NM NORTH OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 31 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY)
26W (CHOI-WAN) ATTEMPTING TO FORM A RAGGED EYE AS IT CONTINUES TO
INTENSIFY. CONVECTIVE BANDING REMAINS EXPANSIVE ON THE EASTERN AND
SOUTHERN FLANKS, WITH NEWER BANDS BEGINNING TO WRAP ON THE
PREVIOUSLY EXPOSED WESTERN FLANK. A 022345Z METOP-B ASCAT PASS
REVEALED AN EXTENSIVE SWATH OF GALE-FORCE WINDS CONTINUING TO
ENCOMPASS ROTA, TINIAN, AND SAIPAN, SUPPORTED BY SURFACE
OBSERVATIONS OF 35-50 KTS ACROSS THE ISLANDS. ADDITIONALLY, A 022115Z 
GPM MICROWAVE PASS REVEALED THE VORTEX HAS BECOME VERTICALLY ALIGNED, 
WITH A FULLY CLOSED LOWER-LEVEL MICROWAVE EYE FEATURE IN THE 37 GHZ 
IMAGE DIRECTLY UNDERNEATH THE NEARLY CLOSED MICROWAVE EYE IN THE 89 
GHZ IMAGE. ENVIRONMENTAL CONDITIONS ARE ASSESSED TO BE HIGHLY 
FAVORABLE WITH LOW (5-10 KTS) VERTICAL WIND SHEAR (VWS), HIGH (130 KJ 
PER CM SQUARED) OCEAN HEAT CONTENT (OHC), AND STRONG POLEWARD AND 
EQUATORWARD OUTFLOW ALOFT. THE INITIAL POSITION IS ASSESSED WITH HIGH 
CONFIDENCE BASED ON THE ASCAT DATA. THE INITIAL INTENSITY IS ASSESSED 
WITH MEDIUM CONFIDENCE, ABOVE AGENCY DVORAK FIXES AND CIMSS ESTIMATES 
DUE TO THE RAPID INTENSIFICATION OF TY 26W.

INITIAL WIND RADII BASIS: 022345Z METOP-B ASCAT DATA

CURRENT STEERING MECHANISM: COMBINATION OF A NORTHERN EXTENSION OF
A NEAR-EQUATORIAL RIDGE CENTERED TO THE SOUTHEAST AND A SUBTROPICAL
RIDGE CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T4.5 - 77 KTS
   CIMSS ADT: 57 KTS AT 022340Z
   CIMSS AIDT: 55 KTS AT 022340Z
   CIMSS D-PRINT: 78 KTS AT 022300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: 34 KT WIND RADII MORE EXPANSIVE THAN
PREVIOUSLY FORECAST BASED ON THE 022345Z ASCAT DATA.

FORECAST DISCUSSION: TY 26W IS FORECAST TO CONTINUE NORTH-
NORTHEASTWARD FOR THE NEXT 24 HOURS, STEERED BY THE NORTHERN
EXTENSION OF A NEAR-EQUATORIAL RIDGE (NER) CENTERED TO THE
SOUTHEAST AS THE EASTWARD PASSAGE OF A SHORTWAVE TROUGH TO THE NORTH 
IS CURRENTLY WEAKENING THE WESTWARD EXTENSION OF A SUBTROPICAL RIDGE
(STR) CENTERED TO THE NORTHEAST. BY TAU 24, THIS STR IS EXPECTED TO
REORIENT AND BECOME THE PRIMARY STEERING MECHANISM, CAUSING A
NORTH-NORTHWESTWARD TURN. 26W IS EXPECTED TO ROUND THE STR AXIS
BETWEEN TAUS 60 AND 72, ACCELERATING NORTHEASTWARD FOR THE
REMAINDER OF THE FORECAST PERIOD. BEGINNING AT TAU 72, THE ONSET OF
EXTRATROPICAL TRANSITION (ETT) IS EXPECTED AS 26W ENTERS AN AREA OF
COOLER SSTS AND APPROACHES THE BAROCLINIC ZONE, ULTIMATELY
COMPLETING ETT BY TAU 96. REGARDING INTENSITY, 26W IS EXPECTED TO
CONTINUE INTENSIFYING OUT TO A PEAK OF 115 KTS BY TAU 36 AS IT WILL
REMAIN IN FAVORABLE ENVIRONMENTAL CONDITIONS. AFTER THIS POINT, A
STEADY WEAKENING TREND IS EXPECTED AS 26W ENTERS AN AREA OF LOWER
(LESS THAN 75 KJ PER CM SQUARED) OHC AND LOSES ITS EQUATORWARD
OUTFLOW CHANNEL. VWS AND RESULTANT DRY AIR ENTRAINMENT WILL INCREASE 
BY TAUS 72 TO 96 WITH THE ONSET OF ETT AND INDUCE FURTHER WEAKENING, 
HOWEVER 26W IS EXPECTED TO MAINTAIN A STRONG AND EXPANSIVE WIND FIELD 
AT THE TIME IT COMPLETES ETT.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT ON THE
OVERALL STEERING INFLUENCE BETWEEN THE NER AND STR AND SUBSEQUENT 
TRACK, BUT DISAGREES ON TRACK SPEED BEGINNING AT TAU 60, WITH JGSM, 
GALWEM, AND THE BULK OF AI-BASED GUIDANCE ACCELERATING 26W MUCH FASTER 
WITH THE BEGINNING OF ETT WHILE GFS, GEFS MEAN, AND NAVGEM REMAIN THE 
SLOWEST OUTLIERS, LEADING TO AN ALONG-TRACK SPREAD OF 680 NM BY TAU 
96. THE JTWC FORECAST IS THUS PLACED WITH MEDIUM CONFIDENCE OUT TO TAU 
72, CLOSELY IN BETWEEN THE MULTI-MODEL AND AI CONSENSUS AND LOW
CONFIDENCE THEREAFTER, HEDGING CLOSER TO THE TRACK SPEED DEPICTED
BY AI GUIDANCE. REGARDING INTENSITY, MODELS ARE IN GOOD AGREEMENT
ON AN INTENSIFICATION AND PEAK BETWEEN TAUS 36 AND 48 FOLLOWED BY
GENERAL WEAKENING THEREAFTER, WITH THE EXCEPTIONS OF GFS AND NAVGEM
BASED COAMPS-TC, WHICH MAINTAIN A STEADIER INTENSITY FOR THE
DURATION OF THE FORECAST PERIOD ON THE LOW END OF THE GUIDANCE 
PACKAGE. THE OFFICIAL JTWC INTENSITY FORECAST IS ASSESSED WITH MEDIUM 
CONFIDENCE OUT TO TAU 72, IN GOOD AGREEMENT WITH THE MULTI-MODEL AND 
GOOGLE DEEPMIND AND ASSESSED WITH LOW CONFIDENCE THEREAFTER DUE TO THE 
UNCERTAINTY REGARDING WEAKENING DURING ETT.

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