WDPN31 PGTW 060900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 19W (NINETEEN)
WARNING NR 05//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION 19W (GUCHOL), LOCATED APPROXIMATELY 277 NM
SOUTH-SOUTHWEST OF TAIPEI, TAIWAN, HAS TRACKED NORTH-
NORTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTI-
SPECTRAL SATELLITE AND A 060712Z SSMIS 91GHZ MICROWAVE IMAGE
DEPICTS A FULLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH
FLARING CONVECTION DISPLACED OVER 50 NM TO THE WEST-SOUTHWEST. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE. THE INITIAL
INTENSITY IS SET AT 25 KNOTS BASED ON A 060203Z ASCAT PASS SHOWING
25 KNOT WINDS WRAPPING AROUND THE LLCC. DESPITE WARM SEA SURFACE
TEMPERATURES OF 28 TO 29 DEGREES CELSIUS, THE ENVIRONMENT
SURROUNDING TD 19W IS DOMINATED BY MODERATE EASTERLY VERTICAL WIND
SHEAR (20 TO 25 KNOTS). TD 19W CONTINUES TO TRACK TOWARD THE
NORTHWEST TOWARD A WEAKNESS IN THE STEERING SUBTROPICAL RIDGE DUE
TO A LONGWAVE TROUGH APPROACHING EASTERN CHINA.
3. FORECAST REASONING.
A. NO CHANGE TO THE FORECAST TRACK PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
B. TD 19W IS FORECAST TO CONTINUE TRACKING NORTH-NORTHWESTWARD
THROUGHOUT THE FORECAST PERIOD, UNDER THE INFLUENCE OF THE WESTERN
PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) FAR TO THE
NORTHEAST. HOWEVER, THE TRACK FORECAST IS COMPLICATED BY THE
SHEARED STRUCTURE OF THE SYSTEM. GIVEN THAT DEEP CONVECTION HAS
SHEARED COMPLETELY AWAY FROM THE LLCC, THE CENTER IS CURRENTLY
BEING ADVECTED IN A MORE NORTHWARD DIRECTION TOWARD TAIWAN.
HOWEVER, ASSUMING DEEP CONVECTION WILL REDEVELOP NEAR THE LLCC
OVERNIGHT AT DIURNAL MAXIMUM LIKE IT DID YESTERDAY, TD 19W SHOULD
RESUME A MORE NORTH-NORTHWESTWARD TRACK TOWARD A WEAKNESS IN THE
RIDGE AXIS IMPOSED BY A LONGWAVE TROUGH APPROACHING EASTERN CHINA.
TO ACCOUNT FOR THESE TWO SCENARIOS, THE OFFICIAL JTWC TRACK
FORECAST LIES WELL TO THE EAST OF THE GLOBAL MODEL GUIDANCE BUT TO
THE WEST OF THE MESOSCALE MODELS (HWRF AND COAMPS-TC). GIVEN THAT
THE CONTINUED PRESENCE OF VERTICAL WIND SHEAR, TD 19W IS EXPECTED
TO REMAIN WEAK THROUGH LANDFALL, WITH DISSIPATION OVER EASTERN
CHINA AROUND TAU 48. DUE TO THE HIGH UNCERTAINTY IN THE MESOSCALE
CONVECTIVE EVOLUTION OF TD 19W IN A HIGH-SHEAR ENVIRONMENT, THERE
IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK.//
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