WPAC: WIPHA - Post-Tropical - Discussion

[cycloneye]

FORECAST DISCUSSION: TS 09W HAS CONTINUED TO SLOW DOWN BUT HAS ALSO
RATHER STUBBORNLY TRACKED ON A MORE WESTWARD TRACK, VICE TURNING
MORE SOUTHWESTWARD, SUCH THAT THE TRACK FORECAST HAS SHIFTED
NORTHWARD BY ABOUT 30NM WITH THIS FORECAST. THERE IS NO CHANGE TO
THE OVERALL TRACK PHILOSOPHY, AS THE SYSTEM WILL BE STEERED BY THE
RIDGE TO THE NORTH THROUGHOUT THE FORECAST PERIOD. THE SYSTEM DOES
APPEAR TO BE SLOWING DOWN AS THE RIDGE TO THE NORTH APPEARS TO BE
BREAKING DOWN A BIT, THEREBY WEAKENING THE STEERING GRADIENT.
HOWEVER, THE FLATTER TRAJECTORY MEANS THE SYSTEM WILL HAVE LESS
TIME OVER THE GULF OF TONKIN, BEFORE MAKING LANDFALL IN VIETNAM.
LANDFALL IS EXPECTED TO OCCUR NEAR TAU 24 IN THE VICINITY OF
HAIPHONG, OR THE OFFSHORE ISLANDS (CAT BA OR BAI TU). AFTER MAKING
LANDFALL, THE SYSTEM WILL TRACK TOWARDS THE WEST INTO THE NORTHERN
PART OF LAOS. IN TERMS OF INTENSITY; THE EXCESSIVE VORTEX TILT
EVIDENT IN THE MICROWAVE AND RADAR DATA, AS WELL AS THE SHORTENED
TIME THE SYSTEM WILL SPEND OVER WATER, WILL LIMIT ITS
INTENSIFICATION POTENTIAL. THE SYSTEM WILL BE BACK OVER WATER
IMMINENTLY AND ONCE THE ENTIRETY OF THE WIND FIELD MOVES OFFSHORE,
DEEP CONVECTION IS EXPECTED TO REFORM AROUND THE CENTER. THE
PERSISTENT SHEAR WILL BE DIFFICULT TO OVERCOME TO ANY SIGNIFICANT
DEGREE, BUT EVEN STILL, THE SYSTEM IS FORECAST TO INTENSIFY ABOUT
10 KNOTS PRIOR TO MAKING LANDFALL IN VIETNAM, REACHING A PEAK OF AT
LEAST 55 KNOTS JUST PRIOR TO MOVING ASHORE. AFTER LANDFALL, THE
SYSTEM WILL STEADILY WEAKEN AND ULTIMATELY DISSIPATE OVER NORTHERN
LAOS NO LATER THAN TAU 72.

[cycloneye]

[cycloneye]

FORECAST DISCUSSION: TS 09W IS FORECAST TO CONTINUE TRACKING
WEST-SOUTHWESTWARD, STEERED BY A WEAK SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTHEAST. AS THE SYSTEM REMAINS OVER VERY WARM
SSTS OF THE GULF OF TONKIN, SLIGHT INTENSIFICATION IS POSSIBLE WITH
PEAK SUSTAINED WINDS REACHING 55 KTS WITHIN THE NEXT 6-12 HOURS,
BEFORE TERRAIN INTERACTION STARTS AFFECTING THE WIND FIELD AND
ULTIMATELY STRUCTURE OF THE VORTEX. ADDITIONALLY, THE ONGOING
IMPACT OF HIGH VWS WILL IMPOSE A LIMIT ON POTENTIAL STRENGTHENING.
LANDFALL IS FORECAST TO OCCUR SOON AFTER TAU 12, RESULTING IN A
STEADY DEGRADATION OF THE LOW-LEVEL CIRCULATION OVER LAND, DUE TO
THE INTERACTION WITH THE COMPLEX TERRAIN OF NORTHERN VIETNAM AND
INCREASINGLY HOSTILE SHEAR. COMPLETE DISSIPATION IS ANTICIPATED BY
OR BEFORE TAU 48.

[sasha_B]

Reintensification seems to have been limited so far, and neither JTWC nor CMA forecast substantial intensification before landfall in Vietnam. ATCF Best Track has held intensity at 50 kts, 984 hPa.

[cycloneye]

FORECAST DISCUSSION: TROPICAL STORM (TS) 09W IS TRACKING SLOWLY
WEST-SOUTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE SUBTROPICAL
RIDGE AND IS FORECAST TO MAKE LANDFALL IN ABOUT 06-09 HOURS. AFTER
MAKING LANDFALL, THE SYSTEM WILL TRACK INLAND ON A WESTWARD
TRAJECTORY AND DISSIPATE RAPIDLY BY TAU 36.

[cycloneye]

Last warning.

REMARKS:
220900Z POSITION NEAR 20.3N 105.9E.
22JUL25. TROPICAL STORM 09W (WIPHA), LOCATED APPROXIMATELY 45 NM
SOUTH-SOUTHEAST OF HANOI, VIETNAM, HAS TRACKED WEST-SOUTHWESTWARD
AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL
IMAGERY REVEALS THE EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC)
AS THE SYSTEM HAS CONTINUED TO DECAPITATE OVER THE LAST SIX HOURS.
THE INITIAL POSITION IN THE RED RIVER DELTA REGION IS MADE WITH
HIGH CONFIDENCE DUE TO THE EXPOSED NATURE OF THE CIRCULATION.
THE SYSTEM WILL CONTINUE TO DISSIPATE OVER LAND DURING THE NEXT
24 HOURS WHILE DRIVEN WESTWARD ON THE SOUTHERN PERIPHERY OF THE
SUBTROPICAL RIDGE TO THE NORTH. THIS IS THE FINAL WARNING ON THIS
SYSTEM BY THE JOINT TYPHOON WRNCEN PEARL HARBOR HI