By PDC’s Senior Weather
Specialist Glenn James
The Pacific Disaster Center’s (PDC Global) Thursday, September 7, 2023, Tropical Cyclone Activity Report…for the Pacific Ocean, the Indian Ocean, and adjacent Seas
Current Tropical Cyclones:
Tropical Cyclone 11E (Jova)…is located approximately 645 NM west-southwest of the southern tip of Baja California
Tropical Cyclone 12W (Yun-yeung)…is located approximately 207 NM southwest of Yokosuka, Japan
Northeast Pacific Ocean:
Tropical Cyclone 11E Jova
JOVA STILL A MAJOR HURRICANE OVER OPEN WATERS
According to the NHC Advisory number 14…
Jova is moving toward the west-northwest near 17 mph (28 km/h), and this general motion with a gradual decrease in forward speed is expected over the next few days.
Maximum sustained winds are near 125 mph (205 km/h) with higher gusts. Jova is a category 3 hurricane on the Saffir-Simpson Hurricane Wind Scale. Continued weakening is forecast during the next several days.
Hurricane-force winds extend outward up to 25 miles (35 km) from the center and tropical-storm-force winds extend outward up to 140 miles (220 km).
Central North Pacific…
There are no tropical cyclones, nor any areas of disturbed weather under investigation by the CPHC.
Western Pacific, Indian Ocean and adjacent Seas:
Tropical Cyclone 12W (Yun-yeung)
According to the JTWC Warning number 11…
Sustained winds were 40 knots…with gusts to near 50 knots
Animated visible satellite imagery depicts a system struggling to survive in the face of persistent, strong, southerly wind shear. Analysis of multiple bands of satellite imagery, nearby upper-air soundings suggests that tropical storm 12W is already in the early phases of a phase transition. High resolution model fields and recent scatterometer data show the remnants of a frontal boundary lying just to the northeast of the system. Induced by the strong upper-level southwesterly flow, the low level circulation center (llcc) is starting to rope out along a southwest-northeast direction along the old boundary to the north. Animated water vapor imagery shows a wedge of dry air punching in from the west, right into the inner core of the system.
The system continues to slow down as it rides up the western side of the subtropical ridge (str) to the east, but begins to run into a transient low to mid-level anticyclone passing through the northern Sea of Japan. The environment has steadily worsened and is now considered unfavorable, with the system facing very high wind shear, significant dry air entrainment and the early phases of extratropical transition, which are offsetting the robust poleward outflow. lastly, the remnants of 11W (Kirogi) were last seen about 180 NM south of the current position, moving very quickly to the northeast. The remnant circulation will be absorbed into the southeastern periphery of 12W within the next few hours.
TS 12W is now tracking northward along the north-south oriented str to the east, but is slowing down at a rapid clip this morning, with a developing anticyclone to the north blocking its path. The anticyclone to the north is transient however and will have moved east of Hokkaido by 24 hours, allowing TS 12W to resume its trek towards central honshu. landfall is expected to occur between 12 and 18 hours in the vicinity of Hamamatsu.
As described above, the system is already showing signs of beginning the early phases of a transition to a shallow, asymmetric warm core system. However, wind speeds are likely to remain where they are for the time being, especially as the system approaches the coast and gets a boost from terrain induced funneling effects. Convection is however, likely to be unable to maintain itself in any organized fashion from now through landfall, in the face of the extremely high wind shear.
As the system makes landfall, it is likely to stretch out towards the northeast, with a secondary area of low pressure and circulation spinning off east of the Japanese Alps and tracking to the northeast along the east coast of Honshu. The primary circulation the system will steadily weaken after landfall, with what remains following an erratic path, likely making the appearance of jumping to a new area of low pressure off the northern coast of Honshu by 36 hours.
Dissipation as a tropical cyclone is anticipated no later than 48 hours, but possibly much earlier if the system cannot make it intact over the Japanese Alps.