Advisories

WDPN31 PGTW 050300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 051//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.1N 140.0E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 131 NM WEST-NORTHWEST OF CHICHI JIMA
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 31 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS THE LOW
LEVEL CIRCULATION CENTER (LLCC) OF TYPHOON (TY) 30W (IN-FA)
BECOMING INCREASINGLY EXPOSED AS THE CENTRAL CONVECTION CONTINUES
TO BE SHEARED TO THE EAST. A 042121Z MWI MICROWAVE SUITE REVEALED
THAT THE MICROWAVE EYE FEATURE IN THE 37 GHZ IMAGE HAS
STRENGTHENED, ONCE AGAIN FULLY CLOSED AND RELATIVELY ALIGNED WITH
THE CENTER IN THE 89 GHZ IMAGE. A 042032Z RCM-2 PASS SUPPORTS THIS
MARGINALLY IMPROVED CONVECTIVE STRUCTURE WITH A BAND OF ENHANCED
WINDS EXPANDING FROM THE NORTHERN SEMICIRCLE AND EXPANSIVE
GALE-FORCE WINDS TO THE SOUTHEAST. ENVIRONMENTAL CONDITIONS ARE
ASSESSED AS UNFAVORABLE WITH HIGH (35-40 KTS) VERTICAL WIND SHEAR
CAUSING DRY AIR ENTRAINMENT, COOL (25-26 C) SEA SURFACE
TEMPERATURES (SSTS), AND MODERATE OUTFLOW ALOFT, SUPPRESSED BY AN
UPPER-LEVEL TROUGH POSITIONED OVER 30W. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC.
REGARDING INTENSITY, THE SAR DATA SUGGESTS AN INTENSITY OF ROUGHLY
90 KTS WHILE AGENCY DVORAK AND CIMSS OBJECTIVE ESTIMATES CONTINUE
TO DROP WELL BELOW TYPHOON STRENGTH. CONSIDERING THE KNOWN WEAKNESS
OF THE DVORAK METHOD WITH SYSTEMS LACKING CENTRAL CONVECTION AS
WELL AS A PREVIOUSLY OBSERVED HIGH BIAS OF RCM SAR DATA AS COMPARED
WITH OTHER WIND SPEED DATA AND OBSERVATIONS, THE INITIAL INTENSITY
IS ASSESSED WITH LOW CONFIDENCE, AVERAGED BETWEEN THE VARIOUS
INPUTS.

INITIAL WIND RADII BASIS: 042032Z RCM-2 SAR DATA

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE
SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RCTP: T4.0 - 65 KTS
   CIMSS ADT: 57 KTS AT 042030Z
   CIMSS AIDT: 63 KTS AT 042030Z
   CIMSS D-MINT: 46 KTS AT 050103Z
   CIMSS D-PRINT: 47 KTS AT 050100Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30+ KTS
   SST: 25-26 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST HAS BEEN TRUNCATED TO 24
HOURS

FORECAST DISCUSSION: 30W HAS BEGUN ITS NORTHEASTWARD TURN AS IT IS
NOW POLEWARD OF THE AXIS OF THE SUBTROPICAL RIDGE (STR) CENTERED TO
THE SOUTHEAST AND ACCELERATES IN TRACK SPEED. THE SYSTEM IS
EXPECTED TO CONTINUE DOING SO FOR THE REMAINDER OF THE FORECAST
PERIOD. 30W IS FORECAST TO BEGIN  EXTRATROPICAL TRANSITION (ETT) BY
TAU 12 AND COMPLETE BY TAU 24 AS IT BECOMES EMBEDDED UNDERNEATH THE
UPPER-LEVEL JET AND LOSES TROPICAL CHARACTERISTICS. REGARDING
INTENSITY, 30W IS EXPECTED TO STEADILY WEAKEN AS IT CROSSES THE 26
C ISOTHERM IMMINENTLY AND VWS RISES TO OVER 50 KTS BY TAU 24,
ENTRAINING FURTHER DRY, COOL AIR INTO THE CORE. HOWEVER, THE WIND
FIELD OF 30W IS EXPECTED TO CONTINUE EXPANDING AND 30W IS FORECAST
TO COMPLETE ETT WHILE MAINTAINING TYPHOON STRENGTH.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT WITH
THE EXCEPTION OF GALWEM AS A POLEWARD OUTLIER. EXCLUDING GALWEM,
CROSS-TRACK SPREAD IS 50 NM AND ALONG-TRACK SPREAD IS 100 NM AT TAU
24. THE OFFICIAL JTWC FORECAST TRACK IS THUS ASSESSED WITH HIGH
CONFIDENCE, IN GOOD AGREEMENT WITH THE TRACK OF THE MULTI-MODEL
CONSENSUS AND HEDGING BETWEEN ITS TRACK SPEED AND THE SLIGHTLY
FASTER AI CONSENSUS TRACK SPEED. INTENSITY MODEL GUIDANCE CONTINUES
TO BE A BIT MORE SPREAD, WITH HAFS-A AND COAMPS-TC PREDICTING
INTENSIFICATION OUT TO TAU 12, WHILE THE REMAINDER OF MODELS DEPICT
SHARPER WEAKENING. GFS SHOWS RE-INTENSIFICATION AFTER TAU 12, WHILE
GOOGLE DEEPMIND, HWRF, AND DECAY-SHIPS ALL PREDICT STEADY WEAKENING
THROUGHOUT. WHILE NOT DEPICTED IN THE FORECAST, THERE IS A
POSSIBILITY FOR SOME RE-INTENSIFICATION AS IT UNDERGOES ETT AS THE
SYSTEM ENTERS AN AREA OF STRONG TEMPERATURE ADVECTION. THE OFFICIAL
JTWC INTENSITY FORECAST IS THUS ASSESSED WITH MEDIUM CONFIDENCE, IN
GOOD AGREEMENT WITH THE MULTI-MODEL CONSENSUS.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: MEDIUM//
NNNN