WDPN32 PGTW 070300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (FIFTEEN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.8N 154.5E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 610 NM EAST-SOUTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS FLARING
CONVECTION WRAPPING AROUND A LOW-LEVEL CIRCULATION CENTER (LLCC)
THAT IS GRADUALLY BECOMING BETTER ORGANIZED. THE CONVECTION HAS
BECOME PERSISTENT ENOUGH TO INDICATE THAT A TROPICAL DEPRESSION HAS
FORMED, WHICH IS CORROBORATED WITH SCATTEROMETRY DATA. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON A 062306Z AMSU-B
89GHZ MICROWAVE IMAGE, INDICATING THAT THE LLCC IS DISPLACED
SLIGHTLY TO THE SOUTH OF THE DEEPEST FLARING CONVECTION. THE
INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON
SCATTEROMETRY DATA.

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

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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) 15W HAS FORMED AND IS
TRACKING TOWARD THE WEST-NORTHWEST, STEERED BY A SUBTROPICAL RIDGE
(STR) TO THE NORTHWEST. SATELLITE ANALYSES AND SCATTEROMETRY DATA
INDICATE THAT THE LLCC IS STILL SOMEWHAT ELONGATED, WITH THE
DEEPEST CONVECTION DISPLACED SLIGHTLY POLEWARD OF THE LLCC. THE
SYSTEM IS CURRENTLY IN A FAVORABLE ENVIRONMENT FOR INTENSIFICATION,
WITH WARM SEA SURFACE TEMPERATURES (30 TO 31 DEGREES CELSIUS), WEAK
VERTICAL WIND SHEAR (5 TO 10 KNOTS), AND MODERATE RADIAL OUTFLOW.
HOWEVER, NEAR-TERM INTENSIFICATION WILL BE SLOW UNTIL THE LLCC
CONSOLIDATES AND BECOMES VERTICALLY STACKED WITH THE FLARING
CONVECTION, THUS ALLOWING THE WARM CORE TO DEEPEN. THE OFFICIAL
FORECAST CALLS FOR GRADUAL INTENSIFICATION THROUGH TAU 48 TO AN
INTENSITY OF APPROXIMATELY 55 KNOTS. AFTER THAT, THE MORE ORGANIZED
INNER CORE STRUCTURE OF THE SYSTEM SHOULD ALLOW FOR MORE RAPID
DEEPENING. BEYOND TAU 48, THE STEERING STR IS FORECAST TO
SLIDE EASTWARD, WITH A MIDLATITUDE TROUGH PASSING THROUGH JAPAN
INDUCING A SLIGHT BREAK IN THE RIDGE AXIS, WHICH WILL ALLOW TD 15W
TO TURN MORE NORTHWESTWARD. DURING THIS TIME, THE SYNOPTIC SETUP
WILL FAVOR AN ENHANCEMENT OF UPPER-TROPOSPHERIC OUTFLOW, AND TD 15W
IS LIKELY TO EXPERIENCE RAPID INTENSIFICATION. WITH LOW VERTICAL
WIND SHEAR, INCREASING OUTFLOW, AND ABUNDANT WARM WATER, THE
OFFICIAL FORECAST CALLS FOR TD 15W TO REACH SUPER TYPHOON INTENSITY
BY TAU 120.

MODEL DISCUSSION: GLOBAL NUMERICAL MODELS ARE IN GENERAL AGREEMENT
WITH TD 15W TRACKING TOWARD THE WEST-NORTHWEST THROUGH TAU 48
FOLLOWED BY A TURN TOWARD THE NORTHWEST THROUGH THE REST OF THE
FORECAST PERIOD. THE DETERMINISTIC ECMWF AND GFS ARE THE
WESTERNMOST OUTLIERS, TAKING THE CORE OF THE SYSTEM OVER OR NEAR
THE ISLAND OF GUAM. HOWEVER, THE REST OF THE GUIDANCE ENVELOPE,
INCLUDING THE ENSEMBLE GUIDANCE, TAKE TD 15W TO THE EAST OF GUAM.
GIVEN THE PERSISTENCE OF THE LAST TWO GFS RUNS THAT NOTABLY SHIFTED
WESTWARD STARTING AT 12Z, COMBINED WITH THE STEADY WEST-NORTHWESTWARD 
MOTION OF TD 15W OVER THE LAST 12 HOURS, THE PERSISTENT STR TO THE 
NORTH OF THE MARIANAS ISLANDS, AND THE ROBUST UPPER-LEVEL EQUATORWARD 
FLOW EVIDENT IN THE WATER VAPOR SATELLITE IMAGERY ALONG THE EASTERN
FLANK OF THE STEERING STR, THE MORE POLEWARD TRACK APPEARS UNLIKELY. 
AS SUCH, THE OFFICIAL TRACK FORECAST IS PLACED TO THE LEFT OF 
CONSENSUS, FAVORING THE WESTERN PORTION OF THE GUIDANCE ENVELOPE. THE 
INTENSITY GUIDANCE IS RATHER AGGRESSIVE FOR A NEW TD, WITH ALL RAPID 
INTENSIFICATION INDICATORS ACTIVATED. THE INITIAL INTENSITY FORECAST 
THROUGH TAU 48 IS RATHER CONSERVATIVE AS THE SYSTEM ORGANIZES. 
HOWEVER, GIVEN THE AFOREMENTIONED FAVORABLE ENVIRONMENTAL CONDITIONS, 
RAPID INTENSIFICATION IS LIKELY THEREAFTER, AND THE OFFICIAL INTENSITY 
FORECAST TRACKS CLOSELY ALONG WITH HWRF AND COAMPS-TC, BOTH OF WHICH 
ACTUALLY EXCEED THE OFFICIAL JTWC FORECAST OF 130 KNOTS BY TAU 120. 
THE HAFS GUIDANCE IS ON THE LOWER END OF THE INTENSITY GUIDANCE 
ENVELOPE, SUGGESTING THAT TYPHOON INTENSITY WILL NOT BE REACHED UNTIL 
AFTER TAU 96. HOWEVER, THE SHIPS GUIDANCE IS MORE AGGRESSIVE THAN 
CONSENSUS AND LENDS CREDENCE TO THE HWRF AND COAMPS-TC SOLUTIONS. THE 
TRACK FORECAST CONFIDENCE IS MEDIUM THROUGHOUT, AND THE INTENSITY 
FORECAST CONFIDENCE IS MEDIUM THROUGH TAU 72 AND LOW BEYOND, GIVEN THE 
UNCERTAINTIES ASSOCIATED WITH THE BEGINNING OF THE PERIOD OF RAPID 
INTENSIFICATION.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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