Tropical Storm SAUDEL Advisory Sat Oct 24

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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