WDPN31 PGTW 230900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (SAUDEL) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS. 
   TYPHOON 19W (SAUDEL), LOCATED APPROXIMATELY 264 NM SOUTH-SOUTHEAST
OF HONG KONG, HAS TRACKED WEST-NORTHWESTWARD AT 03 KNOTS OVER THE 
PAST SIX HOURS. THE CURRENT POSITION IS BASED ON A 230540Z PGTW 
SATELLITE FIX AND RECENT MICROWAVE SATELLITE IMAGERY INCLUDING A 
230604Z SUOMI NPP ATMS PASS. THE INTENSITY OF 75 KNOTS IS CONSISTENT 
WITH A CONSENSUS OF SUBJECTIVE DVORAK AND AUTOMATED INTENSITY 
ESTIMATES, AND FURTHER SUPPORTED BY 70 TO 75 KNOT WIND SPEEDS 
EVIDENT IN AN ANALYSIS OF GCOM-W AMSR2 DATA FROM 230610Z. TY 19W HAS 
CONTINUED TO TRACK SLOWLY WEST-NORTHWESTWARD OVER THE PAST SIX HOURS 
UNDER THE STEERING INFLUENCE OF WEAK RIDGING CONNECTING TWO 
SUBTROPICAL RIDGE CENTERS SITUATED TO THE WEST AND TO THE EAST OF 
THE SYSTEM. NORTHEASTERLY VERTICAL WIND SHEAR HAS NUDGED HIGHER OVER 
THE PAST SIX HOURS, INDUCING SLOW WEAKENING AND DISPLACING THE 
PRIMARY SHIELD OF PERSISTENT DEEP CONVECTION SLIGHTLY TO THE 
SOUTHWEST OF THE LOW-LEVEL CENTER. THOUGH SHEAR VALUES ARE MODERATE 
(15-20 KNOTS), SEA SURFACE TEMPERATURES (28-29C) AND UPPER-LEVEL 
OUTFLOW TO THE WEST OF THE SYSTEM ARE SUPPORTING THE SYSTEM.   
3. FORECAST REASONING.
   A. FORECAST INTENSITIES ARE SLIGHTLY LOWER THAN REFLECTED IN THE 
PREVIOUS WARNING BASED ON RECENT WEAKENING BELOW THE PREVIOUS 
FORECASTS. HOWEVER, THERE IS NO CHANGE TO THE OVERALL FORECAST 
PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. SUBTROPICAL RIDGING IS EXPECTED TO BUILD TO THE NORTH OF 19W 
OVER THE NEXT SEVERAL DAYS AS AN EXPANSIVE MID-LATITUDE TROUGH, 
WHICH PREVIOUSLY WEAKENED THE STEERING RIDGE, PULLS AWAY. TY 19W 
WILL MOVE STEADILY WESTWARD TO WEST-SOUTHWESTWARD UNDER THE 
CONTINUOUS INFLUENCE OF THE BUILDING RIDGE TO THE NORTH. IN THE NEAR-
TERM, PASSAGE OVER WARM WATER AND SUPPORTIVE OUTFLOW ALOFT SHOULD 
ENABLE THE SYSTEM TO MAINTAIN INTENSITY OR WEAKEN SLOWLY DESPITE THE 
NEGATIVE INFLUENCE OF PERSISTENT NORTHEASTERLY VERTICAL WIND SHEAR. 
HOWEVER, INCREASING SHEAR IS EXPECTED TO TAKE A GREATER TOLL AND 
DRIVE A STEADY WEAKENING TREND AFTER 36 HOURS. LANDFALL IN CENTRAL 
VIETNAM IS ANTICIPATED IN ABOUT 60 HOURS, WITH DISSIPATION OVER LAND 
FOLLOWING BY TAU 72. NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT 
WITH THE OVERALL FORECAST SCENARIO, AND THE MODEL TRACK FORECAST 
CONSENSUS HAS BEEN STEADY FOR THE PAST SEVERAL RUNS. THEREFORE, 
THERE IS HIGH CONFIDENCE IN THE CURRENT JTWC TRACK FORECAST. 
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