Advisories

WDPN33 PGTW 050300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 27W (KOGUMA) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.5N 168.0E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 109 NM NORTH OF KWAJALEIN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A MOSTLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) AND PERSISTENT
CONVECTION LIMITED TO THE NORTHWEST QUADRANT UNDER THE PRESSURE OF
APPARENT SOUTHERLY VERTICAL WIND SHEAR (VWS). A 042124Z ASCAT-B
PASS CAPTURED THE CENTER OF THE LLCC AND REVEALED 25-30 KT WINDS IN
THE NORTHWESTERN QUADRANT. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE EXPOSED LLCC IN ANIMATED MSI. THE INITIAL
INTENSITY OF 30 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
SCATTEROMETER WINDS. THE ENVIRONMENT IS CHARACTERIZED AS MARGINALLY
FAVORABLE, WITH WARM SEA SURFACE TEMPERATURES, LOW TO MODERATE VWS,
WEAK RADIAL OUTFLOW ALOFT, AND PLENTY OF MOISTURE AVAILABILITY.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: THE NORTHWESTERN FLANK OF A NEAR
EQUATORIAL RIDGE (NER) CENTERED TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T2.0 - 30 KTS
   CIMSS D-PRINT: 34 KTS AT 0500Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 27W (KOGUMA) HAS
CONSOLIDATED OVER THE PAST 6 HOURS NORTH OF KWAJAELAIN AND HAS
TRACKED SLOWLY IN A PRIMARILY NORTHWARD DIRECTION OVER THE PAST 24
HOURS. THE SYSTEM IS FORECAST TO TRACK NORTHWARD OVER THE NEXT 12
HOURS UNDER THE STEERING INFLUENCE OF THE NER TO THE SOUTHEAST.
AFTER TAU 12, A MUCH MORE PROMINENT SUBTROPICAL RIDGE TO THE
NORTHEAST WILL BEGIN TO EXERT A STEERING INFLUENCE ON 27W, BECOMING
THE DOMINANT STEERING MECHANISM FOR THE REMAINDER OF THE FORECAST
PERIOD. UNDER THIS INFLUENCE, TD 27W IS FORECAST TO TURN
NORTHWESTWARD IN A COUNTER-CLOCKWISE ARC FROM TAU 12-60, THEN
ESTABLISH A NORTHWESTWARD TRAJECTORY FOR THE REMAINDER OF THE
FORECAST PERIOD. IN TERMS OF INTENSITY, THE SYSTEM IS EXPECTED TO
CONSOLIDATE SLOWLY IN A MARGINALLY FAVORABLE ENVIRONMENT WITH ONLY
MODEST INTENSIFICATION THROUGH TAU 60. THE RATE OF INTENSIFICATION
IS EXPECTED TO INCREASE AFTER TAU 60 ONCE THE VORTEX FULLY
DEVELOPS, BECOMES MORE VERTICALLY ALIGNED, AND TAPS INTO A POLEWARD
OUTFLOW CHANNEL.

MODEL DISCUSSION: MODEL TRACK GUIDANCE, WITH THE EXCEPTION OF
NAVGEM, IS IN GOOD AGREEMENT ABOUT THE OVERALL TRAJECTORY, HAVING A
200 NM CROSS-TRACK SPREAD AT TAU 120. THERE IS GREATER DISPARITY IN
THE TRACK SPEED, WITH AN ALONG-TRACK SPREAD OF 370 NM AT TAU 120.
GFS IS THE SLOWEST SOLUTION WHILE THE UKMET ENSEMBLE IS THE
FASTEST. DESPITE THE SPREAD, THE TWO MODELS OFFSET EACH OTHER IN THE
MULTI-MODEL CONSENSUS, WHICH LANDS AMONG THE BULK OF REMAINING
GUIDANCE. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE
AFOREMENTIONED CONSENSUS THROUGHOUT THE FORECAST PERIOD. WITH THE
EXCEPTION OF GFS-BASED COAMPS-TC AS A SIGNIFICANT HIGH INTENSITY
OUTLIER, THE INTENSITY GUIDANCE IS IN GOOD AGREEMENT ABOUT THE
INTENSIFICATION TREND THROUGHOUT THE FORECAST PERIOD. THE JTWC
INTENSITY FORECAST FOLLOWS THE MEAN OF THE REMAINING GUIDANCE,
SLIGHTLY BELOW THE CONSENSUS DUE TO THE ANOMALOUSLY HIGH COAMPS-TC
CONTRIBUTION. 

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