Advisories

WDPN31 PGTW 240900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (IN-FA) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.1N 165.7E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 150 NM NORTHWEST OF KWAJALEIN
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 30W IS INTENSIFYING. ANIMATED ENHANCED INFRARED
(EIR) SATELLITE IMAGERY DEPICTS DEEP CONVECTIVE BURSTS ALONG THE
WESTERN AND EASTERN SIDES OF THE CIRCULATION, WITH CONVECTION
WRAPPING TOWARD THE OBSCURED LOW-LEVEL CIRCULATION CENTER. CURVED
BANDING FEATURES AND UPPER-LEVEL OUTFLOW ARE EXPANDING OUTWARD. A
232132Z ASCAT-B PASS REVEALED A COMPACT CIRCULATION WITH 40-50 KT
WINDS NEAR THE CENTER. THE ENVIRONMENT IS FAVORABLE FOR
INTENSIFICATION, CHARACTERIZED BY VERY WARM SEA SURFACE
TEMPERATURES (SST) OF 29-30 DEGREES CELSIUS, LOW VERTICAL WIND
SHEAR (VWS), AND MODERATE RADIAL OUTFLOW ALOFT. THE INITIAL
POSITION IS PLACED WITH LOW CONFIDENCE BASED ON THE APPARENT
MID-LEVEL CIRCULATION CENTER IN SHORTWAVE-INFRARED IMAGERY BETWEEN
TWO CONVECTIVE MASSES. AGENCY FIXES ARE WIDELY SPREAD ACROSS A
60-NM AREA, AND THE ASCAT PASS IS APPROXIMATELY 11 HOURS OLD. THE
INITIAL INTENSITY IS ASSESSED AT 50 KTS WITH LOW CONFIDENCE, BASED
PRIMARILY ON THE HIGHEST CREDIBLE ASCAT-B WINDS AND SUPPORTED BY
THE IMPROVED CONVECTIVE SIGNATURE SINCE THE SCATTEROMETER PASS.
THIS ASSESSMENT IS ABOVE THE AVAILABLE SUBJECTIVE AND AUTOMATED
INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   PHFO: T3.0 - 45 KTS
   CIMSS SATCON: 39 KTS AT 240214Z
   CIMSS ADT: 41 KTS AT 240540Z
   CIMSS AIDT: 35 KTS AT 240540Z
   CIMSS D-MINT: 44 KTS AT 240251Z
   CIMSS D-PRINT: 42 KTS AT 240540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 30W IS MEANDERING EQUATORWARD IN A WEAK AND
COMPETING STEERING ENVIRONMENT BETWEEN A NEAR-EQUATORIAL RIDGE
(NER) TO THE SOUTHEAST AND A SUBTROPICAL RIDGE (STR) TO THE
NORTHWEST. OVER THE NEXT 12 HOURS, A TROUGH EJECTING OFF THE
EASTERN COAST OF HONSHU WILL SHIFT THE STR SOUTHWARD AND WESTWARD
WHILE THE NER BUILDS. THE RESULTANT STEERING PATTERN WILL DRIVE TS
30W NORTH-NORTHWESTWARD THROUGH TAU 48. AFTER TAU 48, A DEEP TROUGH
APPROACHING HONSHU WILL CAUSE THE STR TO REORIENT AND CONSOLIDATE
DUE NORTH OF THE SYSTEM, RESULTING IN AN ABRUPT WESTWARD TURN. IF
THE EASTWARD SHIFT OF THE STR OCCURS MORE SLOWLY THAN FORECAST, TS
30W MAY FIRST TURN NORTHEASTWARD, DELAYING THE WESTWARD TURN BY
12-24 HOURS. CONDITIONS WILL REMAIN HIGHLY CONDUCIVE FOR
SIGNIFICANT INTENSIFICATION THROUGH TAU 36 AS TS 30W TRAVERSES VERY
WARM SST WITHIN A LOW-SHEAR ENVIRONMENT. THE FORECAST CALLS FOR
RAPID INTENSIFICATION (RI) TO 90 KTS BY TAU 36. AFTERWARD, A
PASSING UPPER-LEVEL TROUGH MAY TEMPORARILY DISRUPT THE POLEWARD
OUTFLOW CHANNEL. ADDITIONALLY, UPWELLING OF COOLER WATERS WHILE THE
SYSTEM SLOWLY TURNS WESTWARD MAY TAKE EFFECT. THEREAFTER,
UPPER-LEVEL DIVERGENCE WILL INCREASE AGAIN, ALLOWING THE SYSTEM TO
INTENSIFY MORE STEADILY.

MODEL DISCUSSION: THE SPREAD AMONG TRACK GUIDANCE INCREASED
SLIGHTLY THIS CYCLE, PARTICULARLY WITH RESPECT TO THE TIMING OF THE
TURN BETWEEN TAU 36 AND TAU 72. GFS, THE GEFS ENSEMBLE MEAN,
HAFS-A, AND JGSM DEPICT AN INITIAL NORTHEASTWARD TURN NEAR TAU 36
BEFORE A SHARP WESTWARD TURN. IN CONTRAST, THE AI-BASED GUIDANCE
GENERALLY FAVORS A SHARPER WESTWARD TURN BEGINNING NEAR TAU 48. THE
JTWC FORECAST TRACK IS SIMILAR TO THE PREVIOUS FORECAST AND IS
PLACED NEAR THE AI-GUIDANCE MEAN, WHICH LIES SLIGHTLY SOUTH OF THE
MULTI-MODEL CONSENSUS (CONW). SEVERAL RAPID INTENSIFICATION AIDS
ARE TRIGGERED, AND NEARLY ALL GUIDANCE MEMBERS DEPICT SIGNIFICANT
INTENSIFICATION THROUGH TAU 36. THE JTWC INTENSITY FORECAST BRINGS
THE SYSTEM TO 90 KTS BY TAU 36, ALTHOUGH SOME GUIDANCE REACHES 105
KTS. HAFS-A INTENSIFIES THE SYSTEM TO 115 KTS BY TAU 60. THE JTWC
INTENSITY FORECAST IS PLACED NEAR THE MIDDLE OF THE GUIDANCE
ENVELOPE THROUGH TAU 48, THEN TRENDS TOWARD THE UPPER PORTION OF
THE ENVELOPE THEREAFTER, LEANING TOWARD COAMPS-TC AND DEEPMIND.
ABOUT 40 PERCENT OF DEEPMIND ENSEMBLE MEMBERS BRING THE SYSTEM TO
SUPER TYPHOON INTENSITY BY TAU 96.

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