Advisories

WDPN31 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 039//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.3N 141.7E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 152 NM SOUTH OF IWO TO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY)
30W (IN-FA) WITH AN UPPER LEVEL CIRCULATION CENTER (ULCC) BECOMING
SLIGHTLY SHEARED TO THE EAST FROM THE LOW LEVEL CIRCULATION CENTER
(LLCC) AS MODERATE (20 KTS) NORTHWESTERLY MID-LEVEL VERTICAL WIND 
SHEAR (VWS) CONTINUES TO ENTRAIN DRY AIR INTO THE WESTERN FLANK OF THE 
SYSTEM. A 012144Z F-16 MICROWAVE SUITE REVEALS THE UPPER LEVEL 
CONVECTION ERODED ON THE WESTERN FLANK WHILE THE LOWER LEVEL MAINTAINS 
A COMPACT MICROWAVE EYE FEATURE OFFSET TO THE WEST. A 012324Z METOP-B 
ASCAT PASS DEPICTED ONLY THE NORTHERN SEMICIRCLE OF THE WIND FIELD 
MAINTAINING OVER 50 KTS, WHILE THE SOUTHWESTERN QUADRANT HAS THE 
WEAKEST WIND SPEEDS. ENVIRONMENTAL CONDITIONS ARE ASSESSED AS 
MARGINALLY UNFAVORABLE, WITH ROBUST POLEWARD OUTFLOW ALOFT AND LOW (5-
10 KTS) DEEP-LAYER VWS BEING OFFSET BY THE AFOREMENTIONED ENHANCED 
MID-LAYER VWS, DRY AIR ENTRAINMENT, AND CONTINUED UPWELLING OF COOLER 
(25-26 C) SEA SURFACE TEMPERATURES (SSTS). THE INITIAL POSITION IS 
PLACED WITH HIGH CONFIDENCE BASED ON THE COMBINED SATELLITE IMAGERY. 
THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE 
SPREAD OF AGENCY DVORAK FIXES AND CIMSS OBJECTIVE ESTIMATES.

INITIAL WIND RADII BASIS: 012324Z METOP-B ASCAT DATA

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT BETWEEN TWO
SUBTROPICAL RIDGES CENTERED TO THE EAST AND WEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T4.0 - 65 KTS
   CIMSS SATCON: 69 KTS AT 012144Z
   CIMSS ADT: 69 KTS AT 012330Z
   CIMSS AIDT: 66 KTS AT 012330Z
   CIMSS D-MINT: 68 KTS AT 020030Z
   CIMSS D-PRINT: 60 KTS AT 020030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 5-10 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: OCEANIC UPWELLING OF COOLER SSTS; ENHANCED
MID-LEVEL VWS

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: TY 30W HAS BEGUN A SLIGHT NORTHWESTWARD TURN AND 
INCREASE IN TRACK SPEED AS THE STEERING RIDGE COMPLEX COMPRISED OF TWO 
SUBTROPICAL RIDGES (STRS) CENTERED TO THE EAST AND WEST SHIFT 
WESTWARD, MAINTAINING 30W WITHIN THE COL BETWEEN THE TWO AND THE
EASTERN STR SLOWLY BUILDS. BY TAU 24, A PASSING MID-LATITUDE TROUGH TO 
THE NORTH WILL WEAKEN THE WESTERN STR, CAUSING 30W TO TURN POLEWARD AS 
THE EASTERN STR BECOMES THE PRIMARY STEERING INFLUENCE. 30W IS 
EXPECTED TO BE POLEWARD OF THE STR AXIS BY TAU 60 AND ACCELERATE 
NORTHEASTWARD THEREAFTER. EXTRATROPICAL TRANSITION (ETT) IS EXPECTED 
TO BEGIN AT TAU 72 AS 30W APPROACHES THE BAROCLINIC ZONE AND CROSSES 
THE 26 C ISOTHERM, COMPLETING ETT BY TAU 96. REGARDING INTENSITY, 30W 
IS EXPECTED TO MAINTAIN INTENSITY OUT TOTAU 36 AS TRACK SPEED 
INCREASES, ALLOWING 30W TO MOVE OVER WARMER (27-28 C) SSTS AND ESCAPE 
ITS COOL WAKE. MODERATE INTENSIFICATION IS FORECAST FROM TAU 36 TO TAU 
60 AS 30W NEARS THE AXIS OF THE EASTERN STR AND OUTFLOW ALOFT IS 
ENHANCED, FOLLOWED BY STEADY WEAKENING THEREAFTER AS IT CROSSES THE 26 
C ISOTHERM AND VWS SHARPLY INCREASES, FURTHER ENTRAINING DRY AIR. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE REMAINS IN FAIR AGREEMENT OUT 
TO TAU 72 WITH A CROSS-TRACK SPREAD OF 120 NM. BEYOND THIS POINT, 
TRACK SPEED CONTINUES TO BE THE LARGER AREA OF DISAGREEMENT, WITH AN 
ALONG-TRACK SPREAD OF 730 NM AT TAU 96 BETWEEN THE SLOWEST, UKMET 
ENSEMBLE, AND THE FASTEST, THE AI ECMWF DETERMINISTIC. THE OFFICIAL 
JTWC FORECAST TRACK IS THUS PLACED WITH MEDIUM CONFIDENCE OUT TO TAU 
72 AND LOW CONFIDENCE THEREAFTER, IN GOOD AGREEMENT WITH THE AI 
CONSENSUS UNTIL TAU 96, AT WHICH POINT IT LAGS BEHIND, FAVORING THE 
SLIGHTLY SLOWER TRACK SPEEDS OF COAMPS-TC, HAFS-A, AND GFS. MODEL 
INTENSITY GUIDANCE HAS COME INTO SLIGHTLY BETTER AGREEMENT, WITH ALL 
MODELS DEPICTING A PLATEAU OR SMALL 5 KT FLUCTUATIONS OUT TO TAU 36. 
AFTER THIS, HAFS-A, COAMPS-TC, DECAY-SHIPS, AND HWRF DEPICT RE-
INTENSIFICATION WHILE GOOGLE DEEPMIND AND GFS HAVE STEADIER WEAKENING 
THROUGHOUT. THE OFFICIAL JTWC FORECAST INTENSITY IS THUS ASSESSED WITH 
MEDIUM CONFIDENCE OUT TO TAU 72 AND LOW CONFIDENCE THEREAFTER, IN LINE 
WITH THE MULTI-MODEL CONSENSUS. THERE IS A POSSIBILITY FOR SMALL
FLUCTUATIONS IN INTENSITY OUT TO TAU 36, BUT IS NOT REPRESENTED IN
THE FORECAST.

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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