WDPN31 PGTW 180900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W (SIXTEEN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.6N 113.6E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 284 NM SOUTH OF HONG KONG
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS PERSISTENT
DEEP CONVECTION PLACED OVER AN ELONGATED CIRCULATING REGION
SPANNING FROM THE SOUTHWEST TO THE NORTHEAST THAT HAS RAPIDLY
ORGANIZED AND CONSOLIDATED OVER THE LAST SIX HOURS AS SHEAR HAS
LESSENED TO A MODERATE 10-15KTS WITH A SHARP GRADIENT OF HIGH SHEAR
TO THE NORTH OF THE CIRCULATION. LOW-LEVEL CLOUD BANDING IS
APPARENT WRAPPING IN TO THE PARTIALLY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC). WATER VAPOR IMAGERY DEPICTS STRONG POLEWARD OUTFLOW
INTO A DIFFLUENT UPPER-LEVEL NORTHEASTERLY FLOW. INTENSITY DATA HAS
BEEN SPARSE, BUT TWO LOCAL SHIP OBSERVATIONS REPORT SUSTAINED WIND
SPEEDS ABOVE 25KTS WITHIN THE BROAD CIRCULATION. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED
CIRCULATION WRAPPING INTO A CLEAR-CUT LLCC. THE INITIAL INTENSITY
OF 25 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AFOREMENTIONED SHIP OBSERVATIONS ABOVE WARNING CRITERIA AND THE
AGENCY FIXES LISTED BELOW.

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

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.0 - 25 KTS
   RJTD: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. 

FORECAST DISCUSSION: TWO INVESTS WERE PRESENT IN THE SOUTH CHINA
SEA EARLIER, 98W AND 99W, AND THE TWO ASSOCIATED VORTICITY MAXIMA
WERE EXPECTED TO CONSOLIDATE AND DEVELOP IN THE WESTERN POSITION
LABELED 98W CLOSER TO VIETNAM. SINCE THEN, SHEAR HAS BECOME HIGH
BETWEEN 25-30KTS IN THE POSITION PREVIOUSLY KNOWN AS 98W AND THE
CIRCULATION HAS TRACKED OVER LAND. THE SHEAR IN THE EASTERN PORTION
OF THE SOUTH CHINA SEA HAS LESSENED SIGNIFICANTLY ALLOWING FOR THE
SYSTEM TO CONSOLIDATE, HOWEVER THE ENVIRONMENT IS CONSIDERED
MARGINALLY FAVORABLE DUE TO THE TIGHT GRADIENT LEADING TO HIGH
SHEAR NORTH OF THE CIRCULATION. TROPICAL DEPRESSION 16W IS FORECAST
TO TRACK WEAKLY SOUTHWESTWARD WHILE CONTRACTING INTO A TIGHTER AND
MORE SYMMETRIC CIRCULATION FOR THE NEXT 24 HOURS BEFORE CURVING TO
THE NORTHWEST WHILE DRIVEN BY THE STR TO THE NORTH. WHILE THE
SYSTEM CONTRACTS, IT EXPECTED TO INTENSIFY TO 35KTS WHILE IN A
REGION OF LOW TO MODERATE SHEAR, FAVORABLE DIVERGENCE IN THE
UPPER-LEVEL ENVIRONMENT. AS THE SYSTEM APPROACHES LAND, TALL
MOUNTAIN RANGES WILL INTERFERE WITH THE CIRCULATION RESULTING IN
WEAKENING JUST PRIOR TO LANDFALL THAT WILL CONTINUE DUE TO
TOPOGRAPHIC INTERACTION.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
REGARDING TRACK BUT VARIES DEPENDING ON EXACTLY WHERE THE LOW-LEVEL
CIRCULATION CENTER DEVELOPS. GFS FORMS THE SYSTEM FARTHER TO THE
WEST, WHILE ECMWF FORMS THE SYSTEM FARTHER TO THE EAST. BOTH MODELS
AGREE REGARDING INTENSITY WITH A PEAK AROUND 35KTS WITHIN 24 HOURS.

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