Advisories

WDPN32 PGTW 041500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (TWENTYTHREE) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.4N 137.8E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 240 NM SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 18 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A SMALL
CONVECTIVE MASS OVER AN OBSCURED LOW-LEVEL CIRCULATION CENTER. AN
EARLIER 040030Z ASCAT-C PASS REVEALED A COMPACT CIRCULATION WITH
20-25 KT WINDS NEAR THE CENTER. 12 HOURS LATER, A PARTIAL ASCAT
PASS REVEALED 35-40 KT WINDS ALONG THE EASTERN PERIPHERY,
INDICATING THAT THE COMPACT LLCC HAS RAPIDLY SPUN UP. THEREFORE,
THIS SYSTEM HAS BEEN DESIGNATED A 40-KT TROPICAL STORM. THE
ENVIRONMENT IS MARGINAL, CHARACTERIZED BY VERY WARM SEA SURFACE
TEMPERATURES (SST) OFFSET BY MODERATE VERTICAL WIND SHEAR. THE
COMPACT CORE IS EMBEDDED IN DEEP-LAYER SOUTHERLY FLOW. THE INITIAL
POSITION WAS ASSESSED WITH LOW CONFIDENCE. THE INITIAL INTENSITY
HAS BEEN SET AT 40 KTS WITH HIGH CONFIDENCE BASED ON THE ASCAT
DATA, WHICH IS SIGNIFICANTLY HIGHER THAN THE SUBJECTIVE DVORAK
ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TS 23W WILL CONTINUE ON A NORTH-NORTHWESTWARD
TRAJECTORY ALONG THE WESTERN FLANK OF A STR TO THE EAST. A TURN
TOWARD THE WEST IS INDICATED IN THE FORECAST AS THE SHALLOW SYSTEM
REACHES THE NORTHERN EXTENT OF CYCLONIC CAULDRON OF THE MONSOON
TROUGH, WHERE THE LOW-LEVEL FLOW IS EASTERLY. THE ENVIRONMENT AHEAD
OF TS 23W WILL NOT IMPROVE DUE TO PERSISTENT SHEAR AND INTERACTION
WITH THE LARGER CIRCULATION OF TS 22W. THEREFORE, THE FORECAST
CALLS FOR THE MINIATURE VORTEX TO SUCCUMB TO THE UNFAVORABLE
CONDITIONS, WITH A GRADUAL WEAKENING TREND AFTER TAU 12.

MODEL DISCUSSION: THE TRACKER GUIDANCE IS TIGHTLY PACKED THROUGH
TAU 36. AFTER THAT TIME, SOME MODELS LOSE THE CIRCULATION BECAUSE
IT OPENS UP INTO A TROUGH. EVENTUALLY, THE BROADER VORTEX OF TS 22W
WILL CATCH UP TO TS 23W AND TEAR IT APART. THE INTENSITY AIDS
LARGELY DEPICT A FLAT OR DOWNWARD TREND THROUGH THE PERIOD. THE
JTWC INTENSITY FORECAST DECREASES TOWARD GFS AT THE LATTER TAUS AND
PREDICTS DISSIPATION NO LATER THAN TAU 60.

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