WDPN31 PGTW 102100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 01W (ONE) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.2N 114.3E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 350 NM EAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: EASTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A SMALL
AND FULLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC), WITH
LOCALIZED FLARING CONVECTION FIRING UP NEAR THE ASSESSED CENTER
OVER THE PAST HOUR OR SO. A 101808Z GMI 89GHZ MICROWAVE IMAGE
REVEALS DEEP CONVECTION DISPLACED FAR TO THE WEST-SOUTHWEST OF THE
LLCC, AND A SMALL AREA OF RECENTLY DEVELOPED CONVECTION CLOSE TO
THE LLCC. THE MICROWAVE IMAGE ALSO REVEALS RELATIVELY DRY AIR ALONG
THE NORTHERN PERIPHERY OF THE CIRCULATION. THE INITIAL POSITION IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN THE
ANIMATED EIR. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE, BASED ON THE AVERAGE OF THE AVAILABLE OBJECTIVE AND
SUBJECTIVE INTENSITY FIXES OUTLINED BELOW. THE ENVIRONMENT IS
GENERALLY FAVORABLE FOR INTENSIFICATION, WITH LOW TO MODERATE
EASTERLY SHEAR, WARM SSTS AND MODERATE WESTWARD OUTFLOW ALOFT.

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

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED FAR TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS
   CIMSS ADT: 29 KTS AT 101730Z
   CIMSS AIDT: 28 KTS AT 101730Z
   CIMSS DPRINT: 28 KTS AT 101730Z
   CIMSS DMINT: 24 KTS AT 101808Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: OVER THE PAST 12 HOURS, TROPICAL DEPRESSION
(TD) 01W (ONE) HAS REMAINED QUASI-STATIONARY IN THE CENTRAL SOUTH
CHINA SEA (SCS) ENSCONCED WITHIN THE MONSOON TROF. HOWEVER, AS THE
SYSTEM INTENSIFIES, IT IS EXPECTED TO COME UNDER THE STEERING
INFLUENCE OF THE DEEP-LAYER STR TO THE NORTHEAST AND PUSH OUT TO
THE WEST-NORTHWEST OVER THE NEXT 12 HOURS. THE SYSTEM WILL STEADILY
TURN NORTHWESTWARD TOWARDS HAINAN THROUGH TAU 48, AS IT ROUNDS THE
SOUTHWESTERN PORTION OF THE STEERING RIDGE. LANDFALL ALONG THE
CENTRAL COAST OF HAINAN IS EXPECTED AROUND 0000Z ON THE 13TH AFTER
WHICH THE SYSTEM WILL TRACK NORTHWARD ACROSS THE ISLAND AS IT
REACHES THE RIDGE AXIS. BY TAU 72, THE SYSTEM WILL HAVE CROSSED
HAINAN AND BE MOVING INTO SOUTHERN CHINA. TRACK SPEEDS WILL PICK UP
SHARPLY AFTER THE SYSTEM ROUNDS THE RIDGE AXIS AND BEGINS TO TRACK
NORTHEASTWARD, AHEAD OF AN APPROACHING TROF MOVING IN FROM THE
WEST. IN TERMS OF INTENSITY, THE DUE TO PERSISTENT EASTERLY FLOW
ALOFT, INTENSIFICATION WILL BE SLOW INITIALLY, WITH TD 01W EXPECTED
TO REACH TS STRENGTH WITHIN THE NEXT 12 HOURS. A MORE RAPID PACE OF
INTENSIFICATION IS ANTICIPATED AFTER TAU 24, AS AN UPPER-LEVEL
ANTICYCLONE IS FORECAST TO DEVELOP OVER TOP OF THE SYSTEM,
DRAMATICALLY IMPROVING UPPER-LEVEL OUTFLOW. THE SYSTEM IS FORECAST
TO REACH TYPHOON STRENGTH BY TAU 48, AND MAY REACH PEAK INTENSITY
JUST PRIOR TO LANDFALL ON HAINAN. AFTER MAKING LANDFALL, THE SYSTEM
WILL RAPIDLY WEAKEN DUE TO TERRAIN INTERACTION AND INCREASING
SHEAR. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN RELATIVELY
GOOD AGREEMENT, AT LEAST THROUGH THE INITIAL 72 HOURS OF THE
FORECAST. THE GFS INTERPOLATED TRACKER TAKES THE CENTER OF THE
SYSTEM THE FURTHEST WEST, OVER THE WESTERN COAST OF HAINAN, WHILE
THE ECMWF AND JGSM TRACKERS BRING THE CENTER OVER THE EASTERN TIP
OF HAINAN, AND THE REMAINDER OF THE CONSENSUS MEMBERS LYING BETWEEN
THE TWO OUTLIERS. THE JTWC TRACK LIES JUST WEST OF THE CONSENSUS
MEAN, HEDGED TOWARDS THE ECMWF AIFS FORECAST TRACK. CONFIDENCE IS
MEDIUM THROUGH TAU 72. BEYOND TAU 72, THE MODEL GUIDANCE DIVERGES
QUICKLY AND SHARPLY, ESPECIALLY IN THE ALONG-TRACK DIRECTION. THE
MAJORITY OF THE CONSENSUS MEMBERS (ALL BUT THE GFS AND GEFS) ARE
POSITIONED FURTHER NORTHEAST AT TAU 72 THAN THE GFS, AND ARE THUS
CAUGHT UP IN THE STRONG SOUTHWESTERLY GRADIENT FLOW AHEAD OF THE
TROF MOVING IN FROM THE WEST. THE TRACKERS REFLECT THIS, WITH THE
MAJORITY OF MEMBERS SHOWING A TAU 120 POSITION NEAR SHANGHAI WHILE
THE GFS REMAINS OVER THE GULF OF TONKIN, RESULTING IN A 1000NM
ALONG-TRACK SPREAD. ENSEMBLE GUIDANCE INDICATES HIGH UNCERTAINTY
AFTER TAU 72 AS WELL, WITH A LARGE ALONG-TRACK SPREAD BETWEEN THE
ECENS AND GEFS SOLUTIONS. THE JTWC FORECAST IS SITUATED NEAR THE
GEFS MEAN TRACK POINT AT TAU 120, BUT CONFIDENCE IS EXTREMELY LOW
DUE TO THE LARGE UNCERTAINTY IN BOTH THE DETERMINISTIC AND ENSEMBLE
GUIDANCE. INTENSITY GUIDANCE IS IN POOR AGREEMENT, WITH A LARGE
SPREAD IN POSSIBLE SOLUTIONS. THE HAFS-A PEAKS THE SYSTEM AT 70
KNOTS, THE COAMPS-TC AT 65, THE HWRF AT 55 AND THE DECAY-SHIPS
(BOTH GFS AND NAVGEM) MUCH LOWER, NEAR 35-45 KNOTS RESPECTIVELY.
ADDITIONALLY, THE RIDE RAPID INTENSIFICATION (RI) AID IS TRIGGERED,
INDICATING A POSSIBLE PEAK OF 100 KNOTS JUST PRIOR TO LANDFALL.
WHILE THIS IS CONSIDERED UNLIKELY AT PRESENT, SIGNIFICANT
INTENSIFICATION REMAINS POSSIBLE. THE JTWC FORECAST IS CONSISTENT
WITH THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD, WITH MEDIUM
CONFIDENCE.  

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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