Tropical Storm KIROGI Advisory Sat Aug 04

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (THIRTEEN)
WARNING NR 01//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 13W (THIRTEEN), LOCATED APPROXIMATELY 385 NM
NORTHWEST OF WAKE ISLAND, HAS TRACKED WESTWARD AT 09 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS
CENTRAL CONVECTION HAS BEEN STEADILY DEVELOPING OVER A WELL
ORGANIZED LOW LEVEL CIRCULATION CENTER (LLCC) FOR THE PAST SIX
HOURS. THE CURRENT INTENSITY OF 25 KNOTS IS BASED ON DVORAK
ESTIMATES FROM PGTW AND RJTD AND IS SUPPORTED BY A RECENT OSCAT PASS
SHOWING BETWEEN 25 TO 30 KNOTS NEAR THE CENTER OF THE LLCC. OVER THE
PAST SIX HOURS THE TRACK OF THE LLCC HAS TURNED TO THE WEST AND
INCREASED SPEED. PRIOR TO THIS THE TRACK HAS BEEN SLOWLY TRACKING
EASTWARD IN A WEAK STEERING ENVIRONMENT. UPPER LEVEL ANALYSIS
INDICATES A STRONG POLEWARD OUTFLOW CHANNEL IS BEING SUPPORTED BY A
TROPICAL UPPER TROPOSPHERIC TROUGH CELL LOCATED TO THE EAST OF THE
LLCC. ADDITIONALLY, ANIMATED WATER VAPOR IMAGERY AND TOTAL
PRECIPITABLE WATER SHOWS A DRY RIBBON IS BUILDING ALONG THE WESTERN
PERIPHERY AROUND THE SOUTHERN PERIPHERY, EXTENDING TO THE
NORTHEASTERN QUADRANT. THIS DRY AIR HAS ALMOST FULLY ENCOMPASSED THE
SYSTEM. VERTICAL WIND SHEAR (VWS) OVER THE AREA IS LOW (05 TO 10
KNOTS). SEA SURFACE TEMPERATURES (SSTS) ARE FAVORABLE (28 TO 29
CELSIUS) ALLOWING CONTINUED DEVELOPMENT.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST
PHILOSOPHY.
   B. TD 13W IS FORECAST TO TURN NORTHWARD AS A DIGGING TROUGH
LOCATED TO THE NORTH WEAKENS THE SUBTROPICAL RIDGE (STR) LOCATED TO
THE NORTHEAST OF TD 13W. A BUILDING NEAR EQUATORIAL RIDGE (NER) TO
THE SOUTHEAST OF TD 13W IS EXPECTED TO BUILD HELPING TO TRACK THE
SYSTEM TO THE NORTH THROUGH TAU 72. MARGINAL UPPER LEVEL ENVIRONMENT
AND SLOWLY DECREASING SSTS WILL KEEP TD 13W FROM DEVELOPING
SIGNIFICANTLY OVER THE NEXT 72 HOURS. THERE IS LOW CONFIDENCE IN THE
CURRENT TRACK FORECAST AS THIS IS THE INITIAL FORECAST.
   C. BEYOND TAU 72, DECREASING SSTS AND THE APPROACH OF A SECONDARY
TROUGH IN THE MID-LATITUDES WILL BEGIN TO ABSORB TD 13W, AND WILL
ALSO MODIFY THE STR, WHICH BECOMES THE DOMINANT STEERING MECHANISM
AFTER TAU 72, INTO A MORE NORTHWEST-SOUTHEAST ORIENTATION. THIS
ORIENTATION WILL CAUSE TD 13W TO TRACK NORTHWESTWARD TOWARDS THE
TROUGH. EXTRATROPICAL TRANSITION IS EXPECTED TO BEGIN AROUND TAU 96.
DUE TO THE HIGH LEVEL OF UNCERTAINTY WITHIN THE TRACK AND INTENSITY
FORECAST, CONFIDENCE IS LOW.//
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