As of 9.16.2021 5pm
TS Chanthu
Chanthu (Philippine name Kiko) is located 528 km west-southwest of Sasebo, Japan, and has moved north-northwestward at 4 km/h (2 knots) over the past 6 hours.
Chanthu is forecast to track north-northeastward to northeastward as the subtropical ridge extension builds into western Japan in response to an approaching midlatitude ridge.
The system will accelerate east-northeastward after 24 hours as strong westerly flow develops over South Korea and Honshu.
There is a short 12-hour window for further development with favorable environmental conditions thus Chanthu is forecast to intensify slightly to 120 km/h (65 knots) in 12 hours.
After 12 hours, wind shear prior to landfall in around 30 hours will increase steadily to 35-45 km/h (20-25 knots), which supports a steady weakening trend as the system approaches northwest Kyushu.
Interaction with land and slightly cooler sea surface temperatures will also contribute to the weakening trend. In 24 hours, south of South Korea, Chanthu will begin to interact with the baroclinic zone and jet, and will weaken to 100 km/h (55 knots) as it begins extra-tropical transition (ETT).
Chanthu will continue to track across western Japan, weaken further and complete ETT in 2 days near central Honshu under jet strength westerlies.
The center should broaden during this phase with deep convection decaying rapidly. The system is expected to maintain gale-force winds, which should become highly asymmetric as it tracks near the Tokyo area.
Forecast guidance is in tight agreement over the next 36 hours with a 67 km spread in solutions at 36 hours. After 36 hours, model guidance diverges as the system gains frontal characteristics and the exact center position broadens and becomes increasingly uncertain.
Overall, confidence in the JTWC forecast track is medium with uncertainty in the recurve timing over the next 36 hours. The JTWC forecast track is positioned close to the JTWC multi-model consensus (CONW).
Chanthu appears to be trying to form an eye but core convection has cycled quickly diurnally therefore there is uncertainty in the peak intensity over the next 12 hours. Thus there is medium confidence in the JTWC intensity forecast.
Maximum significant wave height is 6.1 meters (20 feet).
Winds: 110 kph
Minimum Central Pressure: 985 hPa
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