WDPN34 PGTW 160300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 27W (USAGI) WARNING 
NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.5N 120.3E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 169 NM SOUTH-SOUTHWEST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION 27W (USAGI) WITH A PARTIALLY EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) AND SPARSE CONVECTION THAT IS BEING
SHEARED OFF TO THE NORTHEAST. ENVIRONMENTAL ANALYSIS INDICATES THAT
27W IS IN AN UNFAVORABLE ENVIRONMENT CHARACTERIZED BY WEAK POLEWARD
OUTFLOW ALOFT, MODERATE TO HIGH (20-25 KTS) VERTICAL WIND SHEAR,
WARMISH (26-27 C) SEA SURFACE TEMPERATURES, AND TERRAIN
INTERACTION. THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE
BASED ON THE RAGGED APPEARANCE IN THE ANIMATED MSI. THE INITIAL
INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

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

CURRENT STEERING MECHANISM: LOW TO MID-LEVEL SUBTROPICAL RIDGE
(STR) POSITIONED TO THE EAST, WITH A WEAK EXTENSION TO THE NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS
   DEMS: T3.0 - 45 KTS
   CIMSS DPRINT: 28 KTS AT 160000Z
   CIMSS DMINT: 37 KTS AT 152230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT TO THE WEST AND TERRAIN
INTERACTION WITH SOUTHWESTERN TAIWAN.

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: 27W IS FORECAST TO TRACK NORTHEASTWARD AS IT
MOVES INLAND IN TAIWAN AND CONTINUES TO WEAKEN. INCREASING TERRAIN
INTERACTION, HIGH VERTICAL WIND SHEAR, AND DRY AIR WILL ALL CONTRIBUTE 
TO DEGRADING THE VORTEX. DISSIPATION OVER LAND IN TAIWAN NEAR TAU 24 
IS CURRENTLY FORECASTED, HOWEVER, THERE IS LARGE UNCERTAINTY IN THE 
ACTUAL TRACK 27W TAKES.    

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN EXTREMELY POOR
AGREEMENT, ESPECIALLY AFTER TAU 12 AS MODELS FAN OUT NEARLY IN
EVERY DIRECTION DUE TO THE DISSIPATING VORTEX. THE JTWC TRACK
FORECAST IS PLACED WITH VERY LOW CONFIDENCE AS A RESULT. INTENSITY 
GUIDANCE IS IN BETTER AGREEMENT, SUGGESTING CONTINUED WEAKENING AS 
MODELS QUICKLY LOSE THE VORTEX. THE JTWC INTENSITY FORECAST IS PLACED 
WITH MEDIUM CONFIDENCE DUE TO THIS.

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