WDPN31 PGTW 220300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 26W (TWENTYSIX)
WARNING NR 01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION (TD) 26W (TWENTYSIX), LOCATED APPROXIMATELY
770 NM EAST OF IWO TO, JAPAN, HAS TRACKED NORTHWESTWARD AT 13 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) SHOWS THE MAIN CONVECTION IS SHEARED TO THE SOUTHWEST,
PARTIALLY EXPOSING A BROAD AND ELONGATED LOW LEVEL CIRCULATION. THE
INITIAL POSITION IS BASED ON THE MSI ANIMATION WITH LOW CONFIDENCE.
THE INITIAL INTENSITY OF 25 KNOTS IS BASED ON AN OVERALL ASSESSMENT
OF DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD. UPPER LEVEL ANALYSIS
INDICATES THE SYSTEM IS IN AN AREA OF MODERATE (15-20 KNOT) VERTICAL
WIND SHEAR (VWS) THAT IS OFFSET BY GOOD EQUATORWARD OUTFLOW. THE
CYCLONE IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A LOW- TO
MID-LAYERED SUBTROPICAL RIDGE (STR) TO THE EAST-NORTHEAST.
3. FORECAST REASONING.
A. THIS IS THE INITIAL PROGNOSTIC REASONING BULLETIN AND SETS THE
FORECAST PHILOSOPHY ON THIS SYSTEM.
B. TD 26W IS EXPECTED TO TRACK NORTH AND BEGIN ROUNDING THE
WESTERN EDGE OF THE STEERING STR OVER THE NEXT 12 HOURS. AFTERWARDS,
IT WILL ACCELERATE NORTHEASTWARD AS IT GETS EMBEDDED IN THE
MID-LATITUDE WESTERLIES. INCREASED POLEWARD OUTFLOW WILL OFFSET
INCREASING VWS AND SUSTAIN THE SYSTEM AT TD INTENSITY THROUGHOUT THE
FORECAST PERIOD. BY TAU 12, THE CYCLONE WILL BEGIN EXTRA-TROPICAL
TRANSITION (ETT) AS IT ENTERS THE COLD BAROCLINIC ZONE, BECOMING A
COLD CORE LOW BY TAU 48. THERE IS, HOWEVER, A DISTINCT POSSIBILITY
THAT THE SYSTEM WILL DISSIPATE PRIOR TO ETT DUE TO HIGH VWS. THE
AVAILABLE NUMERIC GUIDANCE IS IN GOOD AGREEMENT. HOWEVER, GIVEN THE
BROAD AND WEAK LOW LEVEL STRUCTURE AND THE UNCERTAINTY IN THE
FORECAST INTENSITY, THERE IS AN OVERALL LOW CONFIDENCE IN THE INITIAL
JTWC FORECAST.//