WDPN31 PGTW 180900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (MITAG) WARNING 
NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.9N 117.4E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 230 NM SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LOW-LEVEL
CIRCULATION CENTER (LLCC) PARTIALLY OBSCURED BY PERSISTENT
CONVECTION ASSOCIATED WITH A MIDLEVEL CIRCULATION OFFSET TO THE
EAST. TROPICAL DEPRESSION (TD) 23W HAS UNEXPECTEDLY TRACKED
WESTWARD OVER THE PAST 6 HOURS; HOWEVER, ANIMATED MSI INDICATES 23W
HAS RESUMED ITS NORTHWESTWARD TRACK. ENVIRONMENTAL ANALYSIS
INDICATES 23W IS IN A MARGINALLY FAVORABLE ENVIRONMENT,
CHARACTERIZED BY LOW VERTICAL WIND SHEAR (5-10 KTS), MODERATE
OUTFLOW ALOFT, AND VERY WARM SEA SURFACE TEMPERATURES (29-30 C),
OFFSET BY DRY AIR ENTRAINMENT FROM THE WEST. THE INITIAL POSITION
IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE PARTIALLY EXPOSED
NATURE OF THE LLCC AND UNEXPECTED TRACK MOTION. THE INITIAL
INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
AGENCY AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

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

CURRENT STEERING MECHANISM: AN ELONGATED SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   DEMS: T2.0 - 30 KTS
   CIMSS SATCON: 44 KTS AT 180507Z
   CIMSS ADT: 43 KTS AT 180540Z
   CIMSS AIDT: 38 KTS AT 180540Z
   CIMSS D-MINT: 25 KTS AT 180530Z
   CIMSS D-PRINT: 26 KTS AT 180610Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE WEST

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TD 23W IS FORECAST TO CONTINUE ITS
NORTHWESTWARD TRACK AS IT IS STEERED BY THE ELONGATED SOUTHWESTERN
PERIPHERY OF THE STR TO THE NORTHEAST. LANDFALL IS EXPECTED TO
OCCUR BETWEEN TAUS 24-36 JUST EAST OF HONG KONG. AFTER WHICH, 23W
IS FORECAST TO TRACK NEARLY DUE WEST AS THE SYSTEM APPROACHES THE
SOUTHERN EXTENT OF THE STR. A PERIOD OF SLIGHT INTENSIFICATION WILL
OCCUR LEADING UP TO LANDFALL. 23W WILL BECOME MORE VERTICALLY
ALIGNED WITH A MOISTENED VORTEX BEFORE LANDFALL, LENDING TO THE
SLIGHT INTENSIFICATION WITH THE STORM PEAKING AT 35 KTS. THE
SOUTHWESTERN QUADRANT IS EXPECTED TO REMAIN WEAKER IN RELATION TO
THE OTHER QUADRANTS. DISSIPATION IS FORECAST TO OCCUR NO LATER THAN
TAU 72 OVER SOUTHERN CHINA.

MODEL DISCUSSION: THE BULK OF JTWC TRACK CONSENSUS MODELS REMAIN IN
GOOD AGREEMENT ON THE NORTHWEST STORM MOTION THROUGH LANDFALL, WITH
JGSM THE OUTLIER, KEEPING 23W FARTHER SOUTH UNTIL TAU 36. AS A
RESULT, THE CROSS-TRACK SPREAD IS 85NM AT TAU 36 AND 105NM AT TAU
72. THE JTWC TRACK FORECAST IS PLACED WITH MEDIUM CONFIDENCE IN
CONCURRENCE WITH THE BULK OF CONSENSUS MEMBERS. INTENSITY GUIDANCE
IS ALSO IN GOOD AGREEMENT WITH 23W PEAKING AT 35 KTS FOLLOWED BY A
PERSISTENT WEAKENING TREND UNTIL DISSIPATION. THEREFORE, THE JTWC
INTENSITY FORECAST IS PLACED WITH HIGH CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: HIGH//
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