WDPS31 PGTW 050300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING NR 
024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.6S 156.4E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 181 NM EAST OF BRISBANE, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 18P (ALFRED) WITH AN EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC) AND CONVECTIVE BANDING BEGINNING TO FORM ALONG THE
SOUTHWESTERN QUADRANT. THE CORE OF THE VORTEX SEEMS TO BE MOISTENING, 
EVIDENT BY THE FORMATION OF CONVECTION CLOSER TO THE CENTER. 
ENVIRONMENTAL ANALYSIS INDICATES THAT 18P IS IN A MARGINAL ENVIRONMENT 
CHARACTERIZED BY MODERATE POLEWARD OUTFLOW ALOFT, HIGH (25-30 KTS) 
VERTICAL WIND SHEAR, DRY AIR WITHIN THE NORTHERN SEMICIRCLE, AND 
BORDERLINE (25-26 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS 
PLACED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN ANIMATED MSI. 
THE INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE 
BASED ON PERSISTENCE FROM A 041849Z SMAP WIND SPEED IMAGE REVEALING 
MAXIMUM WINDS OF 55 KTS (AFTER CONVERSION TO A 1-MINUTE AVERAGE) 
WITHIN THE SOUTHERN PERIPHERY.

INITIAL WIND RADII BASIS: SMAP DATA 

CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF NARROW RIDGING
EXTENDING FROM OVER AUSTRALIA TO SOUTH OF THE VORTEX.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   ABRF: T2.0 - 30 KTS
   CIMSS SATCON: 38 KTS AT 042200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: EXTENSIVE DRY AIR WITHIN THE NORTHERN SEMICIRCLE

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: TC 18P IS FORECAST TO CONTINUE TRACKING
GENERALLY WESTWARD THROUGHOUT THE FORECAST PERIOD AS IT TRACKS
TOWARD THE EASTERN COAST OF AUSTRALIA. TRACK SPEEDS ARE EXPECTED TO
BE SLOW DURING ITS APPROACH DUE TO THE NEAR EQUATORIAL RIDGE
POSITIONED TO THE NORTH CAUSING COMPETING STEERING. LANDFALL IS
FORECAST TO OCCUR JUST BEFORE TAU 48, NEARLY DIRECTLY OVER
BRISBANE. REGARDING INTENSITY, 18P IS FORECAST TO MAINTAIN INTENSITY
UP UNTIL LANDFALL AS SHEAR REMAINS HIGH, SEA SURFACE TEMPERATURES
REMAIN COOL, AND OUTFLOW REMAINS MODERATE. HOWEVER, THE VORTEX MAY
MOISTEN UP FURTHER BEFORE LANDFALL, WHICH COULD CAUSE MILD
INTENSIFICATION. AS THE SYSTEM TRACKS FURTHER INLAND, TERRAIN
INTERACTION WILL CAUSE THE SYSTEM TO DISSIPATE AROUND TAU 72. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN VERY GOOD
AGREEMENT CONCERNING THE TRACK OF 18P, ESPECIALLY UP UNTIL THE TIME
OF LANDFALL, WITH A MERE 20 NM CROSS-TRACK SPREAD AT THAT TIME.
MODELS BEGIN TO SLIGHTLY DIVERGE AFTER TAU 48, DUE TO DIFFERENCES
IN REACTION TO TERRAIN EFFECTS. GFS AND ITS ENSEMBLE MEAN TAKE THE
VORTEX NORTHWESTWARD WHILE THE REMAINDER OF GUIDANCE KEEPS IT
MOVING WESTWARD. THE JTWC IS PLACED WITH HIGH CONFIDENCE, CLOSE TO
THE MUTI-MODEL CONSENSUS. INTENSITY GUIDANCE IS IN GOOD AGREEMENT
AS WELL, WITH A CONSTANT INTENSITY OF AROUND 55-60 KTS THROUGH TAU
36 WITH WEAKENING THEREAFTER. AS A RESULT, THE JTWC INTENSITY
FORECAST IS ALSO PLACED WITH HIGH CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: HIGH//
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