Tropical Storm SON-TINH Advisory Paz, 28.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 24W (SON-TINH) WARNING NR 17//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 24W (SON-TINH), LOCATED APPROXIMATELY 205 NM SOUTH-
SOUTHEAST OF HANOI, VIETNAM, HAS TRACKED WEST-NORTHWESTWARD AT 11
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY (EIR) REVEALS THE 20 NM EYE HAS FILLED IN OVER THE PAST SIX
HOURS. A 271425Z AMSU MICROWAVE IMAGE SHOWS THAT TY 24W HAD TWO
CONCENTRIC EYE WALLS AT THE TIME. THE INITIAL POSITION IS BASED ON
THE ANIMATED EIR AND FIXES FROM PGTW AND RJTD WITH GOOD CONFIDENCE.
THE INITIAL INTENSITY IS ASSESSED AT 105 KNOTS BASED ON DVORAK
ESTIMATES OF 102 KNOTS FROM PGTW, KNES AND RJTD. UPPER-LEVEL
ANALYSIS INDICATES THE SYSTEM IS DIRECTLY BENEATH A RIDGE AXIS IN AN
AREA OF LIGHT TO MODERATE (10-15 KNOTS) VERTICAL WIND SHEAR. JUST TO
THE NORTH ARE PROGRESSIVELY INCREASING AND DIVERGENT WINDS
ASSOCIATED WITH THE STRONG WESTERLIES. ANIMATED WATER VAPOR IMAGERY
REVEALS THE PREVIOUS BURST OF ENHANCED OUTFLOW ASSOCIATED WITH A
PASSING MID-LATITUDE TROUGH IS BEGINNING TO SUBSIDE, THOUGH STILL
ROBUST. THE CYCLONE IS NOW TRACKING ALONG THE SOUTHWESTERN PERIPHERY
OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) ANCHORED JUST SOUTH OF
TAIWAN. OBSERVED WINDS AT HUE, VIETNAM, 100 NM SOUTH OF THE CURRENT
POSITION, HAVE BEEN PREDOMINANTLY FROM THE SOUTHWEST AT 5-15 KNOTS
OVER THE PAST SIX HOURS.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. TY SON-TINH WILL CONTINUE TO TRACK WEST-NORTHWESTWARD UNTIL IT
MAKES LANDFALL ALONG THE NORTHERN COAST OF VIETNAM PRIOR TO TAU 24.
AFTER LANDFALL, THE CYCLONE WILL DEFLECT POLEWARD AS THE STR
FLATTENS IN RESPONSE TO THE AFOREMENTIONED TROUGH. THE SYSTEM IS
FORECAST TO MAINTAIN ITS INTENSITY OVER THE NEXT 12 HOURS GIVEN THE
AMPLE OUTFLOW AND PERENNIALLY WARM WATERS OF THE GULF OF TONKIN.
AFTER THIS TIME, THE WARM MOIST AIR FROM THE EQUATOR WILL BE
RESTRICTED BY THE INDOCHINESE PENINSULA AND THE INFLUX OF RELATIVELY
COOLER AND DRIER CONTINENTAL AIR FROM CHINA WILL BEGIN TO WEAKEN THE
SYSTEM. NEVERTHELESS, TY 24W WILL STILL BE AT A MODEST TROPICAL
STORM STRENGTH WHEN IT APPROACHES HANOI. THE SYSTEM IS FORECAST TO
DISSIPATE BY TAU 72 NEAR THE CHINESE BORDER DUE TO LAND INTERACTION
AND INCREASING SHEAR. THE NUMERICAL MODEL GUIDANCE IS IN GOOD
AGREEMENT UP TO TAU 36, AFTER WHICH THE MODELS SPREAD DUE TO
UNCERTAINTIES IN THE INTERACTION OF THE SYSTEM WITH THE MID-LATITUDE
WESTERLIES AND TERRAIN EFFECTS. THERE IS HIGH CONFIDENCE IN THE
TRACK FORECAST UP TO TAU 36.  AFTER TAU 36, SOME OF THE GUIDANCE
SUGGESTS THE REMNANTS OF TY 24W MAY CURVE MORE SHARPLY, AND RE-
EMERGE BACK OVER THE GULF OF TONKIN. IN THIS ALTERNATE SCENARIO, THE
SYSTEM WOULD BE CLOSELY MONITORED FOR SIGNS OF REGENERATION.//
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