WDPN31 PGTW 210300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (WIPHA) WARNING NR 
011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.5N 109.4E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 198 NM EAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: WESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) INDICATES TROPICAL
STORM (TS) 09W IS STILL RELATIVELY WELL ORGANIZED, WITH
WELL-DEFINED CONVECTIVE BANDS WRAPPING INTO AN OBSCURED LOW LEVEL
CIRCULATION CENTER (LLCC). ANIMATED RADAR IMAGERY SHOWS THE LLCC
SITUATED EAST OF BEIHAI, CHINA AT THE 0000Z HOUR, AND THE SURFACE
OBSERVATION FROM BEIHAI SHOWED WINDS FROM THE NORTHWEST AT 17
KNOTS, SUPPORTING THE INITIAL POSITION TO THE EAST OF THE STATION.
A 202318Z SSMIS 91GHZ MICROWAVE IMAGE REVEALED A STRONGLY TILTED
VORTEX, WITH THE UPPER-LEVEL ROTATION DISPLACED WELL TO THE WEST OF
THE LLCC DUE TO THE PERSISTENT MODERATE NORTHEASTERLY SHEAR. THE
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
RADAR AND SURFACE OBSERVATION DATA. THE INITIAL INTENSITY IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE CIMSS D-PRINT AND
D-MINT ESTIMATES NOTED ABOVE. THE ENVIRONMENT IS MARGINALLY
FAVORABLE, WITH VERY WARM SSTS AND STRONG OUTFLOW OFFSET BY
MODERATE NORTHEASTERLY SHEAR AND A STRONGLY TILTED VORTEX.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A NARROW RIDGE
SITUATED OVER CENTRAL CHINA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T2.5 - 35 KTS
   CIMSS D-MINT: 42 KTS AT 202318Z
   CIMSS D-PRINT: 44 KTS AT 210030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: LAND PROXIMITY. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 09W HAS CONTINUED TO SLOW DOWN BUT HAS ALSO
RATHER STUBBORNLY TRACKED ON A MORE WESTWARD TRACK, VICE TURNING
MORE SOUTHWESTWARD, SUCH THAT THE TRACK FORECAST HAS SHIFTED
NORTHWARD BY ABOUT 30NM WITH THIS FORECAST. THERE IS NO CHANGE TO
THE OVERALL TRACK PHILOSOPHY, AS THE SYSTEM WILL BE STEERED BY THE
RIDGE TO THE NORTH THROUGHOUT THE FORECAST PERIOD. THE SYSTEM DOES
APPEAR TO BE SLOWING DOWN AS THE RIDGE TO THE NORTH APPEARS TO BE
BREAKING DOWN A BIT, THEREBY WEAKENING THE STEERING GRADIENT.
HOWEVER, THE FLATTER TRAJECTORY MEANS THE SYSTEM WILL HAVE LESS
TIME OVER THE GULF OF TONKIN, BEFORE MAKING LANDFALL IN VIETNAM.
LANDFALL IS EXPECTED TO OCCUR NEAR TAU 24 IN THE VICINITY OF
HAIPHONG, OR THE OFFSHORE ISLANDS (CAT BA OR BAI TU). AFTER MAKING
LANDFALL, THE SYSTEM WILL TRACK TOWARDS THE WEST INTO THE NORTHERN
PART OF LAOS. IN TERMS OF INTENSITY; THE EXCESSIVE VORTEX TILT
EVIDENT IN THE MICROWAVE AND RADAR DATA, AS WELL AS THE SHORTENED
TIME THE SYSTEM WILL SPEND OVER WATER, WILL LIMIT ITS
INTENSIFICATION POTENTIAL. THE SYSTEM WILL BE BACK OVER WATER
IMMINENTLY AND ONCE THE ENTIRETY OF THE WIND FIELD MOVES OFFSHORE,
DEEP CONVECTION IS EXPECTED TO REFORM AROUND THE CENTER. THE
PERSISTENT SHEAR WILL BE DIFFICULT TO OVERCOME TO ANY SIGNIFICANT
DEGREE, BUT EVEN STILL, THE SYSTEM IS FORECAST TO INTENSIFY ABOUT
10 KNOTS PRIOR TO MAKING LANDFALL IN VIETNAM, REACHING A PEAK OF AT
LEAST 55 KNOTS JUST PRIOR TO MOVING ASHORE. AFTER LANDFALL, THE
SYSTEM WILL STEADILY WEAKEN AND ULTIMATELY DISSIPATE OVER NORTHERN
LAOS NO LATER THAN TAU 72.   

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
STRONG AGREEMENT THROUGH THE FORECAST PERIOD. CROSS-TRACK SPREAD IS
MINIMAL THROUGH LANDFALL AND ONLY SLIGHTLY INCREASES THEREAFTER.
GFS-GEFS HAVE BEGUN TO SLOW DOWN A BIT AND COME MORE IN LINE WITH
THE ECMWF-ECEPS SOLUTIONS IN TERMS OF TRACK SPEED, DECREASING
ALONG-TRACK SPREAD WITH THIS RUN. THE JTWC FORECAST IS POSITIONED
CLOSE TO THE MULTI-MODEL CONSENSUS MEAN WITH HIGH CONFIDENCE.
INTENSITY GUIDANCE IS MIXED, WITH THE MAJORITY OF THE RELIABLE
GUIDANCE SHOWING SLIGHT INTENSIFICATION OR STEADY-STATE INTENSITY
THROUGH TAU 12, FOLLOWED BY RAPID WEAKENING. THE EXCEPTION IS THE
HWRF WHICH SHOWS INTENSIFICATION UP TO 55 KNOTS BY TAU 24. THE JTWC
FORECAST IS POSITIONED CLOSE TO THE HWRF SOLUTION THROUGH THE
FORECAST PERIOD WITH MEDIUM CONFIDENCE.  

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