Tropical Cyclone 09W (Saola) / Tropical Cyclone 10W (Haikui) / Tropical Cyclone 11W (Kirogi))
Thursday, August 31, 2023

Current Snapshot

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By PDC’s Senior Weather
Specialist Glenn James

The Pacific Disaster Center’s (PDC Global) Thursday, August 31, 2023, Tropical Cyclone Activity Report…for the Pacific Ocean, the Indian Ocean, and adjacent Seas

Current Tropical Cyclones:

Tropical Cyclone 09W (Saola)…is located approximately 121 NM east-southeast of Hong Kong

Tropical Cyclone 10W (Haikui)…is located approximately 287 NM south-southeast of Kadena AB

Tropical Cyclone 11W (Kirogi)…is located approximately 623 NM east-southeast of Iwo To


Northeast Pacific Ocean:

>>> Central East Pacific…

An area of low pressure could form several hundred miles south of the southwestern coast of Mexico early next week.

Environmental conditions are expected to be conducive for some gradual development of this system during the middle to later parts of next week while it moves west-northwestward over the central eastern Pacific.

* Formation chance through 48 hours…low…near 0 percent
* Formation chance through 7 days…low…20 percent

Central North Pacific…

>>> Approximately 900 miles south of Hilo, Hawaii…

A weak area of low pressure located far south of Hilo, Hawaii is producing disorganized showers and thunderstorms.

Conditions are forecast to be marginally conducive for some development as it moves west or northwestward over the next few days.

* Formation chance through 48 hours…low…20 percent
* Formation chance through 7 days…low…20 percent


Western Pacific, Indian Ocean and adjacent Seas:

Western Pacific…

Tropical Cyclone 09W (Saola)

According to the JTWC Warning number 34…

Sustained winds were 120 knots…with gusts to near 145 knots

Animated enhanced infrared satellite imagery shows the system has maintained a highly symmetrical and dense central convection; however, the outer eyewall has opened up along the northern quadrant as it struggles to envelope and replace the inner eyewall with its sharply outlined 20 NM eye.

Analysis indicates a favorable environment with very warm sea surface temperatures in the South China Sea, low vertical wind shear, and strong radial outflow. Additionally, TY 09W is slowly undergoing an eyewall replacement cycle which has
slightly weakened the system.

TY Saola will track west-northwestward to westward trajectory under the steering ridge to the north. After 36 hours, a secondary ridge to the west will assume steering, and drive the cyclone southwestward.

The erc is expected to continue to slowly weaken the core of TY 10W; this, in addition to land interaction with the eastern seaboard of China will lead to a gradual weakening to 70 knots by 36 hours after it brushes Hong Kong.

After 36 hours, a more rapid erosion is expected as cool dry air from the Chinese interior intrudes into the low level circulation, knocking down the intensity to 40 knots by 72 hours. Afterward, a scaled down and weaker 35 knot 09W will loop and drift northeastward with the monsoon flow, steered by a shallow near-equatorial ridge to the south.


Tropical Cyclone 10W (Haikui)

According to the JTWC Warning number 15…

Sustained winds were 70 knots…with gusts to near 85 knots

Animated enhanced infrared satellite imagery shows a medium-sized system that has deepened and became more compact with an on and off dimple feature, an indication of a formative eye.

Analysis indicates a favorable environment with very warm sea surface temperatures, low vertical wind shear, and moderate equatorward outflow.

TS Haikui will continue west-northwestward to northwestward under the steering str to the northeast, tracking over Taipei, Taiwan around 72 hours, then make a secondary landfall over the Chinese eastern seaboard near Fuzhou around 96 hours.

The favorable environment will fuel a steady intensification to a peak of 100 knots by 36 hours, as it approaches the Japanese island of Ishigakijima. Afterward, increasing vertical wind shear and later on, land interaction will gradually then rapidly erode the system down to 30 knots by 120 hours as it tracks further inland.


Tropical Cyclone 11W (Kirogi)

According to the JTWC Warning number 9…

Sustained winds were 50 knots…with gusts to near 65 knots

Animated enhanced infrared satellite imagery depicts persistent deep convection obscuring the low-level circulation center (llcc). Animated water vapor imagery depicts a moderate poleward outflow channel enhanced by an upper-level low positioned to the northwest.

Environmental conditions remain marginally favorable due to warm sea surface temperatures, good poleward outflow, offset by moderate (20-25 knot) vertical wind shear.

Tropical Storm 11W (Kirogi) is forecast to track north-northwestward, then northwestward along the western periphery of the ridge through 48 hours. After 48 hours, TS 11W will turn west-northwestward as the ridge to the northeast builds and extends westward. By 72 hours, TS 11W is expected to continue to track west-northwestward, then generally westward toward southern Kyushu through the end of the forecast.

No significant environmental changes are expected over the next 12-24 hours of the forecast, with supportive sea surface temperatures and robust poleward outflow competing with vertical wind shear and dry air entrainment.

The system is forecast to maintain a steady state in terms of intensity, but then begin a steady weakening trend as outflow becomes less favorable and dry air entrainment increases. Thus, the unfavorable environmental factors will result in a gradual weakening trend throughout the forecast period.