WDPN32 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 09W (SAOLA) WARNING NR 038//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.9N 112.7E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 87 NM WEST-SOUTHWEST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 37 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A WELL
DEFINED TYPHOON STRENGTH CIRCULATION TRACKING ALONG THE SOUTHERN
COAST OF CHINA. A 012250Z SSMIS 91GHZ MICROWAVE IMAGE REVEALS THAT
09W IS A SHADOW OF ITS FORMER SELF, WITH FRAGMENTED DEEP CONVECTIVE
CLOUD LINES LIMITED TO THE NORTHERN SEMICIRCLE AND A BROAD,
ILL-DEFINED CIRCULATION CENTER. SURFACE OBSERVATION FROM YANGJIANG
CHINA, REVEAL RECENTLY PLUMMETING SURFACE PRESSURES AND INCREASING
NORTH-NORTHWESTERLY WINDS, ALL OF WHICH ARE SIGNS THAT THE SYSTEM
IS APPROACHING FROM THE EAST. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON MSI AND SSMIS IMAGERY. THE INITIAL
INTENSITY OF 85 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
AGENCY DVORAK INTENSITY ESTIMATES INDICATING T4.5-T5.0, THOUGH THE
PARTIALLY OVERLAND NATURE OF THE CIRCULATION MAY CONTAMINATE THOSE
ESTIMATES. DESPITE GOOD SUPPORT FROM DVORAK ESTIMATES, 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: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T4.5 - 77 KTS
   KNES: T5.0 - 90 KTS

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
24 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 TAUS
36-48, THE SYSTEM WILL BRIEFLY BE OVER WARM 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.
THERE IS INCREASING INDICATION IN BOTH DETERMINISTIC AND ENSEMBLE
GUIDANCE THAT THE STR IN THE LATER TAUS DOES NOT IN FACT
MATRICULATE TO THE NORTHWEST OF THE CIRCULATION. THE POTENTIAL LACK
OF A BLOCKING RIDGE WOULD RESULT IN A CONTINUED WEST-SOUTHWESTWARD
COURSE NORTH OF HAINAN AND ACROSS THE GULF TOWARDS VIETNAM. FOR THE
TIME BEING, THE JTWC FORECAST TRACK FOLLOWS CLOSELY TO THE
MULTI-MODEL CONSENSUS WHICH IS SUPPORTED BY THE PREPONDERANCE OF
EVIDENCE. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIR AGREEMENT THROUGH
TAU 24, AFTER WHICH MEMBERS QUICKLY BIFURCATE. THE FIRST GROUP,
COAMPS-TC (BOTH VERSIONS) AND ECMWF AND ITS ENSEMBLE, CARRY THE
SYSTEM NORTH OF HAINAN AND ACROSS THE GULF TOWARDS VIETNAM. THE
SECOND GROUP CONSISTING OF THE REAMING MEMBERS, GENERALLY FOLLOWS
THE JTWC TRACK FORECAST INTO HAINAN UNTIL DISSIPATION. FOR THESE
REASONS THE JTWC TRACK FORECAST IS PLACED WITH OVERALL LOW
CONFIDENCE. 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 INITIALLY
WITH HIGH CONFIDENCE AND WITH MEDIUM CONFIDENCE THERE AFTER.

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