Western Pacific: 18W(CONSON): landfall South of Dan Nang, 19W(CHANTHU) skirting Taiwan as a CAT 4 Typhoon, 11/15utc updates

TS 18W(CONSON). WARNING 23 ISSUED AT 11/15UTC.SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS CONSON IS FORECAST TO CONTINUE TRACKING WEST-SOUTHWEST AND MAKE LANDFALL NEAR BINH SON, VIETNAM WITHIN THE NEXT 6 TO 12 HOURS. OVER THE NEXT 24 HOURS THE STEERING RIDGE TO THE NORTH IS EXPECTED TO WEAKEN, LESSENING THE STEERING GRADIENT, AND AS THE SYSTEM IS RELATIVELY SHALLOW, THE TRACK AFTER LANDFALL WILL BE HIGHLY INFLUENCED BY THE LOCAL TERRAIN. THUS, ONCE OVER LAND, THE TRACK IS EXPECTED TO TURN NORTHWESTWARD, PARALLELING THE 2600 METER MOUNTAINS THAT LIE TO THE WEST OF BINH SON. TS 18W IS STRUGGLING TO MAINTAIN INTENSITY IN THE FACE OF PERSISTENT MODERATE EASTERLY SHEAR, AND ONCE OVER LAND THIS PROCESS WILL ACCELERATE, LEADING TO DISSIPATION OVER THE RUGGED TERRAIN BY 48H. AS WAS THE CASE WITH THE PREVIOUS FORECAST, THERE REMAINS A POSSIBLE ALTERNATE SCENARIO, IN WHICH THE STEERING RIDGE BREAKS DOWN RELATIVELY QUICKLY, LEADING TO A WEAK STEERING PATTERN, ALLOWING THE SYSTEM TO MAKE A BRIEF LANDFALL BEFORE RETURNING TO SEA, REMAINING QUASI-STATIONARY FOR A PERIOD AND THEN TRACKING NORTHWESTWARD PARALLEL TO THE COASTLINE.

TS 18W.SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY AND ANIMATED VIETNAMESE RADAR DATA INDICATE THE CENTER OF TS 18W IS JUST OFFSHORE NEAR CU LAO RE ISLAND. THE LOW LEVEL CIRCULATION CENTER (LLCC) REMAINS FULLY EXPOSED, WITH MODERATE CONVECTIVE ACTIVITY SHEARED TO THE WEST BY PERSISTENT MODERATE EASTERLY SHEAR. THE EXPOSED LLCC COMBINED WITH THE RADAR DATA LENT HIGH CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY OF 40 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON A BLEND OF MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T3.0 (45 KNOTS) AND AN ADT ESTIMATE OF 34 KNOTS. THE SYSTEM LIES IN AN OVERALL MARGINAL ENVIRONMENT, WITH PERSISTENT MODERATE VERTICAL WIND SHEAR OFFSETTING STRONG WESTWARD OUTFLOW AND WARM SSTS. OHC VALUES ARE LOW CLOSE TO THE COAST, CONTRIBUTING TO THE WEAKENING TREND AS THE SYSTEM HAS SLOWED AS IT APPROACHES THE COASTLINE.

TS 18W(CONSON).MODEL DISCUSSION: TRACK GUIDANCE CONTINUES TO SHOW A HIGH AMOUNT OF UNCERTAINTY, WITH A DRAMATIC AND INCREASING SPREAD IN THE DETERMINISTIC GUIDANCE. NAVGEM CONTINUES TO DEPICT A SOUTHWESTWARD TRACK INTO NORTHERN CAMBODIA. GFS, HWRF, ECMWF AND THE GFS ENSEMBLE NOW SHOW THE SYSTEM STRADDLING THE COAST THROUGH 24H, THEN TURNING SHARPLY NORTH AND PARALLELING THE COAST THROUGH 48H BEFORE A LANDFALL NORTH OF HUE. THE ECMWF ENSEMBLE, UKMET AND ENSEMBLE AND GALWEM ALL SHOW A NORTHWESTWARD TRACK OVER LAND. THE JTWC FORECAST CLOSELY FOLLOWS THE UKMET AND ECMWF ENSEMBLE MEAN TRACKERS WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON A WEAKENING TREND THROUGH THE FORECAST PERIOD, WITH THE EXCEPTION OF HWRF WHICH DEPICTS A 5-KNOT INTENSIFICATION PRIOR TO LANDFALL. THE JTWC FORECAST LIES CLOSE TO THE CONSENSUS MEAN WITH MEDIUM CONFIDENCE.

TY 19W(CHANTHA). WARNING 22 ISSUED AT 11/15UTC.SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TY 19W CONTINUES TO DEMONSTRATE A HIGH DEGREE OF RESILIENCE, AND WHILE WEAKENING SIGNIFICANTLY SINCE THE PREVIOUS ANALYSIS, IT STILL SHOWS SIGNS OF TRYING TO INTENSIFY. THE RAGGED EYE SEEN AT 1200Z HAS BECOME BETTER ORGANIZED AND THE CORE CONVECTION HAS BECOME MORE SYMMETRICAL IN THE SUBSEQUENT HOURS. THE SYSTEM HAS FOUGHT OFF A BAND OF DRY AIR THAT WAS INTRUDING INTO THE CORE, AND HAS PUSHED BACK AGAINST AND EARLIER BOUGHT OF NORTHERLY SHEAR. THE SYSTEM IS MOVING ACROSS A TONGUE OF MODERATELY HIGH OCEAN HEAT CONTENT(OHC) TO THE EAST OF LAN YU ISLAND, SUPPORTING THE IMPROVED REPRESENTATION IN THE ENHANCED INFRA-RED SAT. TY 19W IS MOVING NORTH ALONG THE WESTERN PERIPHERY OF A NORTH-SOUTH ORIENTED STR CENTERED SOUTHEAST OF HONSHU AND IS EXPECTED TO MAINTAIN THIS TRACK THROUGH 48H. THE SYSTEM MAY MOVE SLIGHTLY LEFT OF THE TRACK AS IT INTERACTS WITH AND IS PULLED TOWARDS THE CENTRAL MOUNTAIN RANGE OF TAIWAN, BUT OTHERWISE SHOULD SKIRT THE NORTHEAST TIP OF TAIWAN BEFORE CONTINUING INTO THE EAST CHINA SEA. BY 48H THE SYSTEM WILL MOVE INTO A WEAK STEERING PATTERN, CAUGHT BETWEEN RIDGES CENTERED EAST OF KYUSHU, WEST OF SHANDONG AND OVER SOUTHEASTERN CHINA. IT IS EXPECTED THAT TY 19W WILL REMAIN QUASI-STATIONARY IN THE VICINITY OF SHANGHAI WHILE REMAINING COCOONED IN THIS WEAK STEERING PATTERN THOUGH AT LEAST 96H. BY 120H THE WESTERN RIDGE IS EXPECTED TO ERODE AHEAD OF AN APPROACHING MID-LATITUDE TROUGH WHICH WILL ALLOW THE SYSTEM TO START MOVING EASTWARD BY 120H. IN THE NEAR TERM, TY 19W IS EXPECTED TO MAINTAIN ITS CURRENT INTENSITY AS IT CONTINUES MOVING OVER THE HIGH OHC WATERS. HOWEVER, INCREASING VERTICAL WIND SHEAR AND INTERACTION WITH THE RUGGED TERRAIN OF TAIWAN WILL RESULT IN STEADY WEAKENING AFTER 24H. ONCE THE SYSTEM SLOWS AND REMAINS QUASI-STATIONARY NEAR SHANGHAI IT WILL RAPIDLY COME UNDER THE INFLUENCE OF INCREASING SHEAR, COOLER SSTS, AND CONVERGENT FLOW ALOFT, LEADING TO MORE RAPID WEAKENING THROUGH THE REMAINDER OF THE FORECAST PERIOD.

TY 19W(CHANTHU). SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT AREA SYMMETRICAL DEEP CONVECTION SURROUNDING A RAGGED, ELONGATED 19-KM WIDE EYE. AN 111029Z SSMIS 89GHZ MICROWAVE IMAGE DEPICTED SPIRAL BANDING TO THE SOUTH, WRAPPING INTO A COMPACT LOW LEVEL CIRCULATION CENTER (LLCC), WITH WEDGE OF DRIER AIR DEVOID OF CONVECTION WRAPPING ACROSS THE NORTH TO THE WESTERN SIDE OF THE CONVECTIVE CORE. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE 19-KM EYE AND RADAR DATA FROM TAIWAN. THE INITIAL INTENSITY IS ASSESSED AT 120 KNOTS/CAT 4 WITH MEDIUM CONFIDENCE, HEDGED SLIGHTLY HIGHER THAN THE MAJORITY OF AGENCY CURRENT INTENSITY ESTIMATES, AND ABOVE THE ADT ESTIMATE DUE TO THE PRESENCE OF THE NASCENT EYE FEATURE, WHICH THE ADT IS NOT YET TRACKING. SUBSEQUENT EIR IMAGERY SHOWS THE EYE CLEARING AND WARMING SLIGHTLY, INDICATIVE OF ANOTHER ROUND OF SLIGHT INTENSIFICATION.

BD ENHANCEMENT. EYE FEATURE CLEARING OUT.

TY 19W(SHANTHU).MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT WITH A SPREAD OF 150KM AT 48H. THEREAFTER THERE IS HIGH UNCERTAINTY AS THE MODELS DEPICT A WIDE SPREAD OF POTENTIAL SOLUTIONS, AS WOULD BE EXPECTED IN A WEAK STEERING PATTERN. HOWEVER, ALL MODELS AGREE ON THE OVERALL SCENARIO OF A QUASI-STATIONARY PERIOD BETWEEN 48H AND 96H, FOLLOWED BY AN ACCELERATION EASTWARD, DIFFERING ONLY ON THE TIMING OF THE TURN AND ACCELERATION. HWRF REMAINS THE PRIMARY OUTLIER, TAKING THE SYSTEM WELL INLAND WEST OF SHANGHAI AN THEN ULTIMATELY INTO THE YELLOW SEA. ALL OTHER TRACKERS HOLD THE SYSTEM OFFSHORE OR JUST ONSHORE IN THE VICINITY OF SHANGHAI DURING THE QUASI-STATIONARY PERIOD. THE JTWC FORECAST REMAINS CONSISTENT WITH THE PREVIOUS FORECAST AND THE CONSENSUS MEAN WITH MEDIUM CONFIDENCE THROUGH 72H AND LOW CONFIDENCE THEREAFTER. INTENSITY GUIDANCE ALL SHOW STEADY TO RAPID WEAKENING FROM 00H. THE JTWC FORECAST IS ABOVE ALL GUIDANCE EXCEPT THE TWRF THROUGH THE ENTIRE FORECAST, THOUGH COAMPS-TC CONVERGES WITH THE FORECAST AT 50 KNOTS AT 120H. OVERALL INTENSITY FORECAST CONFIDENCE IS MEDIUM THROUGH 72H, AND LOW THEREAFTER.

TY 19W(CHANTHU). HWRF AT 11/06UTC. 140KNOTS AT +0H.