WDPN31 PGTW 070300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (YAGI) WARNING NR 023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.3N 108.2E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 136 NM EAST-SOUTHEAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 50 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
HAVING MOVED OUT OVER THE OPEN WATERS OF THE GULF OF TONKIN ABOUT
EIGHT HOURS AGO, TYPHOON (TY) 12W (YAGI) HAS STEADILY REORGANIZED
AND RAPIDLY INTENSIFIED AS IT TRACKS TOWARDS AN HISTORICAL LANDFALL
IN NORTHERN VIETNAM. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
DEPICTS A WELL-DEFINED CIRCULATION CENTER WITH VERY STRONG
CONVECTION, AS INDICATED BY A LARGE BAND OF -80C OR COLDER CLOUD
TOPS LAID ACROSS THE SOUTHERN PORTION OF THE CIRCULATION. ANIMATED
RADAR DATA INDICATES A WELL-DEFINED INNER EYEWALL FEATURE WHICH HAS
STEADILY DECREASED IN SIZE SINCE COMPLETING AN EYEWALL REPLACEMENT
CYCLE (EWRC). A 062340Z SSMIS 91GHZ MICROWAVE IMAGE SHOWED THE
STRONGEST EYEWALL CONVECTION IS IN THE SOUTHERN HEMISPHERE, WHILE
THE EYEWALL IS OPEN TO THE NORTHEAST, WHICH ALIGNS WELL WITH THE
LATEST CIMSS DEEP-LAYER SHEAR ANALYSIS, INDICATING 12 KNOTS OF
EAST-NORTHEASTERLY SHEAR. FINALLY, A 062242Z RCM-2 SAR PASS REVEALS
A STRONG EYEWALL IN ALL QUADRANTS IN THE LOWER LEVELS, WITH A
MAXIMUM WIND FIX OF 116 KNOTS. THE INITIAL POSITION IS ASSESSED
WITH HIGH CONFIDENCE BASED ON BOTH THE AFOREMENTIONED SAR AND
MICROWAVE PASSES. THE INITIAL INTENSITY IS ASSESSED WITH HIGH
CONFIDENCE BASED PRIMARILY ON THE SAR PASS, BUT ALSO IS IN LINE
WITH THE ADJUSTED ADT VALUES OF T6.1. THE ENVIRONMENT REMAINS
FAVORABLE FOR A TOUCH MORE INTENSIFICATION PRIOR TO LANDFALL, WITH
VERY WARM SSTS, HIGH OHC, LOW VWS AND GOOD RADIAL OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) OVER CHINA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T5.0 - 90 KTS
   KNES: T5.5 - 102 KTS
   DEMS: T5.5 - 102 KTS
   CIMSS SATCON: 112 KTS AT 062130Z
   CIMSS ADT: 107 KTS AT 070000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 31-32 CELSIUS
   OUTFLOW: STRONG RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY 12W IS QUICKLY APPROACHING THE COAST OF
VIETNAM, WHERE IT IS EXPECTED TO MAKE A HISTORICAL LANDFALL AS ONE
OF THE, IF NOT THE MOST, INTENSE TYPHOON ON RECORD TO MAKE A
LANDFALL IN THIS REGION OF VIETNAM. THE SYSTEM HAS SLOWED DOWN
SLIGHTLY, TO ABOUT 9 KNOTS, AND IS EXPECTED TO MAKE LANDFALL NEAR
HAIPHONG, VIETNAM WITHIN THE NEXT SIX HOURS. IN THE REMAINING TIME
OVER WATER, THERE REMAINS A POSSIBILITY OF A SLIGHT BIT OF
ADDITIONAL INTENSIFICATION, WITH LANDFALL EXPECTED AS A 115-120
KNOT TYPHOON. THE SYSTEM WILL BE VERY SLOW TO WEAKEN DURING THE
INITIAL SIX HOURS OR SO OVER LAND, AS IT TRAVERSES THE MARSHES OF
THE RED RIVER DELTA, DUE TO THE BROWN-WATER EFFECT AND THUS, A 100
KNOT TYPHOON PASSING OVER OR VERY NEAR HANOI IS A DEFINITE
POSSIBILITY WITHIN THE NEXT 12-18 HOURS. AFTER PASSING HANOI, THE
SYSTEM WILL RAPIDLY WEAKEN AS IT MOVES FURTHER INLAND OVER RUGGED
TERRAIN FEATURES. FULL DISSIPATION IS EXPECTED BY TAU 48 OVER FAR
NORTHERN LAOS. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT WITH
MINIMAL CROSS- OR ALONG-TRACK SPREAD THROUGH THE SHORT FORECAST
PERIOD. AFTER THE END POINT OF THE FORECAST, THE NOTABLE EXCEPTION
TO THE STATEMENT ABOVE IS THE GFS, WHICH PULLS A U-TURN AND HEADS
BACK OUT TO SEA BY TAU 96. THE JTWC FORECAST REMAINS CONSISTENT
WITH BOTH THE PREVIOUS FORECAST AND THE CONSENSUS MEAN, WITH HIGH
CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, THAT THE
SYSTEM WILL WEAKEN STEADILY AFTER LANDFALL BEFORE DISSIPATING BY
TAU 48. THE SOLE EXCEPTION IS THE RIDE RAPID INTENSIFICATION AID
WHICH CONTINUES TO STUBBORNLY PREDICT ADDITIONAL INTENSIFICATION
PRIOR TO LANDFALL. THE JTWC FORECAST DOES CALL FOR WEAKENING
THROUGH THE FORECAST PERIOD, BUT WHILE NOT CAPTURED IN THE FORECAST
POINTS, THERE REMAINS A POSSIBILITY OF AN ADDITIONAL 5-10 KNOTS OF
INTENSIFICATION PRIOR TO LANDFALL. 

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