WDPN31 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 14W (KOINU) WARNING 
NR 042//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.0N 111.3E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 180 NM WEST-SOUTHWEST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED PROXY VISIBLE SATELLITE IMAGERY DEPICTS A COMPLETELY
DECOUPLED AND WEAK CIRCULATION, DEVOID OF ANY SIGNIFICANT
CONVECTION. THE PROXY VISIBLE SHOWS A FLARE UP OF CONVECTION SOUTH
OF HONG KONG, BUT THIS IS LIKELY A RESULT OF LOW-LEVEL CONVERGENCE
BETWEEN WEAK SOUTHERLY FLOW AND THE LEADING EDGE OF A SURGE OF
NORTHEASTERLY FLOW PUSHING SOUTH ALONG THE CHINESE COAST. THE
REMNANT LOW-LEVEL VORTEX, EVIDENT IN THE LOW-LEVEL STRATOCUMULUS
FIELD, IS RACING WEST-SOUTHWESTWARD ALONG THE LEADING EDGE OF THE
PREVIOUSLY MENTIONED COLD-SURGE FLOW AND RAPIDLY WEAKENING. THE
INITIAL POSITION IS ASSESSED WITH LOW CONFIDENCE DUE TO THE WEAK
DEPICTION IN BOTH THE PROXY VISIBLE AND THE RADAR DATA. THE INITIAL
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, SET MUCH LOWER THAN
THE DVORAK BASED CURRENT INTENSITY ESTIMATES AND HEDGED TOWARDS THE
FINAL-T NUMBERS, WHICH ARE SET AT T1.5 FROM ALL AGENCIES, AS WELL
AS THE DPRINT ESTIMATE OF 27 KNOTS. WHILE SHEAR IS LOW AND SSTS
WARM, THE DRY MID-LEVEL AIR AND A LACK OF OUTFLOW ALOFT, IS
INHIBITING THE SYSTEM.

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

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A LOW-LEVEL
ANTICYCLONE OVER CHINA AND THE LEADING EDGE OF A STRONG
NORTHEASTERLY SURGE EVENT.  

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T3.0 - 45 KTS
   DEMS: T2.5 - 35 KTS
   CIMSS ADT: 31 KTS AT 091800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK RADIAL

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: TROPICAL DEPRESSION (TD) 14W (KOINU) HAS
UNDERGONE A PERIOD OF EXTREMELY RAPID WEAKENING AS IT HAS STARTING
TRACKING RAPIDLY WEST-SOUTHWESTWARD ALONG THE SOUTHERN COAST OF
CHINA. THE LEADING EDGE OF A STRONG NORTHEASTERLY SURGE, HAVING NOW
REACHED SOUTHWEST OF HONG KONG, WILL CONTINUE TO PUSH TD 14W
SOUTHWESTWARD, OVER OR NEAR ZHANJIANG, AND THEN INTO THE GULF OF
TONKIN. DUE TO A PERSISTENT LACK OF UPPER-LEVEL OUTFLOW AND THE
INFLUENCE OF LOW- TO MID-LEVEL DRY AIR, THE SYSTEM IS EXPECTED TO
CONTINUE WEAKENING, ULTIMATELY DISSIPATING OVER THE GULF OF TONKIN,
NO LATER THAN TAU 36 AND POTENTIALLY MUCH EARLIER. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT
THAT THE SYSTEM WILL TRACK OVER THE LEIZHOU PENINSULA AND THENCE
INTO THE GULF OF TONKIN. HOWEVER, THE MODELS ARE STRUGGLING WITH
THE VERY RAPID WEAKENING AND SEVERAL LOSE THE VORTEX WITHIN THE
FIRST 12 HOURS OF THE MODEL RUN, WHILE THE OTHERS SPREAD OUT TO
ENCOMPASS THE ENTIRE GULF OF TONKIN. THE JTWC TRACK LIES IN THE
CENTER OF THE MODEL ENVELOPE, AND NORTH OF THE CONSENSUS MEAN, WITH
MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE
SYSTEM WILL CONTINUING WEAKENING, AND DISSIPATE BETWEEN TAU 24 AND
TAU 36. 

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