By PDC’s Senior Weather
Specialist Glenn James
The Pacific Disaster Center’s (PDC Global) Thursday, July 27, 2023, Tropical Cyclone Activity Report…for the Pacific Ocean, the Indian Ocean, and adjacent Seas
Current Tropical Cyclones:
Typhoon 05W (Doksuri)…is located approximately 166 NM west-southwest of Taipei, Taiwan
Tropical Cyclone 06W (Khanun)…is located approximately 924 NM south-southeast of Kadena AB
Northeast Pacific Ocean:
Offshore of Southern Mexico…
An area of low pressure could form off the coast of southern Mexico over the weekend to early next week.
Thereafter, some gradual development of this system is possible while it moves generally west-northwestward at 10-15 mph, roughly parallel to the coasts of southern and southwestern Mexico.
* Formation chance through 48 hours…low…near 0 percent
* Formation chance through 7 days…medium…40 percent
Central Pacific Ocean:
There are no tropical cyclones
Western Pacific, Indian Ocean and adjacent Seas:
Typhoon 05W (Doksuri)
According to the JTWC Warning number 27…
Sustained winds were 95 knots…with gusts to near 115 knots
Typhoon 05W (Doksuri) has embarked upon another round of rapid intensification over the past six hours, as it picks up speed towards a rendezvous with the Chinese coast. Animated multi-spectral satellite imagery (msi) shows the system has undergone what is frankly an incredible metamorphosis in a very short period of time. The msi shows a 6 NM wide pinhole eye, while the enhanced infrared (eir) imagery shows cloud top temperatures have drastically cooled. Animated radar imagery and a microwave image show the pinhole eye with an inner eyewall at about 6 NM, surrounded by a moat of clear air and a secondary eyewall at about 50 NM, which is steadily shrinking as the system intensifies.
Clearly the environment is supportive, with low shear, robust poleward outflow into an upper-level low to the north adding to the already strong equatorward outflow. The latest sea surface temperature analysis from NOAA shows the system is moving into an area of extremely warm waters with even warmer waters along the coast of China, likely due to coastal downwelling induced by the Typhoon itself.
From the latest radar data, it appears that TY 05W has finally decided to get a move on, and accelerated towards the northwest over the past six hours. Further acceleration towards the coast is expected as the ridge to the east builds and moves west, tightening the steering gradient. Landfall is still expected in the vicinity of Xiamen, China within the next 12 to 18 hours.
The upper-level low currently southwest of Shanghai is expected to open up into a trough which will extend southward to the west of TY 05W, which will allow the system to continue tapping into the divergent poleward outflow on the east side of the trough. The combination of continued strong outflow and scorching sea surface temperatures will support additional intensification in the period prior to landfall. The current forecast calls for a peak of 115 knots, but a slightly higher peak intensity is not out of the realm of possibility if the eyewall replacement cycle (erc) can fully complete prior to landfall.
Tropical Cyclone 06W
According to the JTWC Warning number 4…
Sustained winds were 30 knots…with gusts to near 40 knots
Animated multi-spectral satellite imagery (msi) depicts a broad circulation with fragmented and disorganized convection firing off, but unable to persist at this time. A scatterometer pass revealed a broad low level circulation center (llcc) with 20-25 knots winds present in all quadrants, but with a radius of maximum winds (rmw) of about 80 NM. A color enhanced microwave image revealed well defined low-level bands but only fragmented areas of moderate convection.
Overall, the environment is currently characterized as marginally favorable, with very warm sea surface temperatures and moderate equatorward outflow. The primary limiting factors at present are the broad nature of the llc and the northerly flow emanating from TY 05W pushing down from the north. However, the system lies right under the inflection point where the outflow from TY 05W splits, and therefore shear has lessened a bit.
TD 06W is expected to move towards the west-northwest for the next 24 hours under the influence of the low to mid-level flow associated with the ridge centered east of the Marianas. Around 24 hours, the system is expected to turn more poleward as the ridge to the east strengthens and moves west and aligns to a more north-south axis. By around 72 hours, the ridge weakens and begins to slide southwestward, and TD 06W runs smack into the very strong subtropical ridge centered near Tokyo. This will force the system to turn left onto a more west-northwestward track from 72 hours through to the end of the forecast period as the primary steering influence shifts to the ridge to the north.
Through the next 36 hours, TD 06W will slowly but steadily consolidate, and the rmw will steadily reduce. Due to the marginal outflow environment and modest amounts of northerly shear, the system will intensify at a slow rate, reaching 40 knots by 36 hours. Around 48 hours however, the environment will rapidly become more favorable. As early as 24 hours, a tutt-cell begins to develop between two very strong upper-level anticyclones, in the vicinity 25N 14E. But through the first 36 hours of the forecast, the tutt is in an unfavorable position for TD 06W.
Between 48 and 72 hours the tutt moves into a highly favorable position to the northwest of TD 06W, and the system will tap into the very strong poleward outflow channel into the eastern side of the strong tutt-cell, supporting explosive intensification after 48 hours, to a peak of at least 115 knots, though a the potential for a much higher peak cannot be ruled out, in the hours between the forecast points. After 96 hours, the system moves into an area of slightly less upper-level outflow and will likely maintain intensity after passing very close to or over the island of Okinawa and moving into the East China Sea.