WDPN32 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 09W (SAOLA) WARNING NR 037//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.0N 113.4E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 48 NM WEST-SOUTHWEST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
PARTIALLY EXPOSED LLCC AS 09W STARTLES THE SOUTHERN COAST OF CHINA.
A RECENT 011630Z SCATTEROMETRY PASS ALONG WITH SEVERAL SURFACE
OBSERVATION NEAR HONG KONG INDICATE THE SYSTEM IS PARTIALLY
OVERLAND AND TRACKING PARALLEL WITH THE COASTLINE. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON EIR IMAGERY,
SURFACE OBSERVATIONS AND SCATTEROMETRY DATA. THE INITIAL INTENSITY
OF 100 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A MAJORITY
OF DVORAK INTENSITY ESTIMATES AS WELL AS AUTOMATED ESTIMATES
INDICATING 95-100KTS THOUGH PARTIAL LANDFALL IS HIGHLY COMPLEX AND
HARD TO PREDICT, THUS MEDIUM CONFIDENCE.

INITIAL WIND RADII BASIS: PERSISTENCE

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T5.0 - 90 KTS
   KNES: T5.5 - 102 KTS
   CIMSS ADT: 90 KTS AT 011730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: PARTIAL LANDFALL OVER SOUTHERN CHINA 

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: TY 09W (SAOLA) IS FORECAST TO CONTINUE
TRACKING GENERALLY WEST-SOUTHWESTWARD AND PARALLEL WITH THE
SOUTHERN COAST OF CHINA TOWARDS THE GULF OF TONKIN. OVER THE NEXT
36 HOURS, INCREASING VERTICAL WIND SHEAR AND LAND INTERACTION ARE
FORECAST TO QUICKLY WEAKEN 09W TO AROUND 40KTS. AS THE SYSTEM
CROSSES THE LUICHOW PENINSULA, DRY AIR ENTRAINMENT JOINS THE
GROWING LIST OF NEGATIVE FACTORS WEAKENING THE SYSTEM. NEAR TAU 48,
THE SYSTEM WILL BRIEFLY BE OVER WARM OPEN WATERS, BUT THIS WILL NOT
BE ENOUGH TO CHANGE HOW THIS STORY ENDS. NEAR TAU 72, AS THE STR TO
THE NORTH BUILDS, THE SYSTEM WILL BE FORCED EQUATORWARD AND OVER
LAND ONCE AGAIN. BY TAU 72, THE SYSTEM WILL BE NEARING DISSIPATION
AND IT WILL EVENTUALLY ACHIEVE THAT GOAL BY TAU 96.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIR AGREEMENT THROUGH
TAU 24, AFTER WHICH MEMBERS QUICKLY SEPARATE INTO TWO GROUPS. THE
FIRST GROUP, COAMPS-TC (GFS VERSION) AND ECMWF, CARRY THE SYSTEM
NORTH OF HAINAN AND ACROSS THE GULF TOWARDS VIETNAM. THE SECOND AND
LARGEST GROUP CONSISTING OF THE REAMING MEMBERS, GENERALLY FOLLOWS
THE JTWC TRACK FORECAST. FOR THESE REASONS THE JTWC TRACK FORECAST
IS PLACED INITIALLY WITH MEDIUM CONFIDENCE AND WITH LOW CONFIDENCE
THERE AFTER. RELIABLE MODEL INTENSITY GUIDANCE IS IN GOOD AGREEMENT
WITH ALL MEMBERS INDICATING SHARP WEAKENING THROUGH TAU 24, AFTER
WHICH A MORE GRADUAL WEAKENING TREND THROUGH THE FORECAST PERIOD.
FOR THIS REASON THE JTWC INTENSITY FORECAST IS PLACED WITH OVERALL
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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