By PDC’s Senior Weather
Specialist Glenn James
The Pacific Disaster Center’s (PDC Global) Saturday, September 2, 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 197 NM east of Hanoi, Vietnam
Tropical Cyclone 10W (Haikui)…is located approximately 160 NM south-southeast of Taipei, Taiwan
Tropical Cyclone 11W (Kirogi)…is located approximately 659 NM east-southeast of Sasebo, Japan – Final Warning
Northeast Pacific Ocean:
>>> Central East Pacific…
A tropical wave is producing disorganized showers and thunderstorms a couple of hundred miles south of the coast of southern Mexico.
Environmental conditions are forecast to be conducive for gradual development of this system, and a tropical depression is expected to form by the middle of next week.
The system is forecast to move westward to west-northwestward, passing well south of mainland
* Formation chance through 48 hours…low…30 percent
* Formation chance through 7 days…high…90 percent
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 09W (Saola)
According to the JTWC Warning number 42…
Sustained winds were 35 knots…with gusts to near 45 knots
Tropical storm 09W (Saola) continues to track inland over southern China, while steadily and rapidly weakening. Animated enhanced infrared satellite imagery continues to show the upper-level circulation center associated with TS 09W moving westward. Meanwhile, a microwave imagery pass shows a remnant eye feature on the southern side of a large mass of deep convection. This depiction matches up with the animated radar data which depicts the low-level circulation center just a shade further south.
Despite a recent jog a bit further north than anticipated, TS 09W is still expected to turn more west and ultimately southwest over the next 12 to 24 hours, emerging into the Gulf of Tonkin around 12 hours. The system will slowly drift southwestward before rounding the western side of Hainan Island by the end of the forecast period.
The system is weakening at a faster pace than originally anticipated, but is still likely to emerge into the Gulf of Tonkin as a weak tropical storm. However, while sea surface temperatures are very warm in the Gulf, the lack of much, or any, upper-level outflow and the envelopment of the circulation in dry air means that it will not be long for this world. The system steadily weakens through the forecast period, before dissipating as a
tropical cyclone off the southwest coast of Hainan by 72 hours.
Tropical Cyclone 10W (Haikui)
According to the JTWC Warning number 23…
Sustained winds were 105 knots…with gusts to near 130 knots
After a 12 hour period where development was arrested, Typhoon 10W (Haikui) looks to have determined to rapidly organize and intensify. Animated enhanced infrared satellite imagery depicts strong convection firing off along the southern periphery, reminiscent of earlier periods of convective blooming. Early indications are that this time around, the shear has lessened, and this should allow for the convection to begin wrapping upshear and ultimately surround the inner-core. The most recent microwave imagery showed a strong eyewall along the entirety of the southern side of the system, but a very weak, eyewall to the north and northwest. Animated radar data shows a similar pattern, with a robust southern eyewall with a weak eyewall to the northwest.
The overall environment is favorable for intensification, save for the dry air to the north.
Based on the latest radar animation, it appears that TY 10W is tracking almost due west, along the southern side of the steering ridge to the north. Some wobbles either side of the forecast track are expected, but overall the system should track west-northwest through the next 12 to 18 hours. Landfall along the southwest coast of Taiwan, near Taitung, is forecast near 18 hours. After landfall, the low level center (llc) will likely turn sharply southwestward due to terrain effects, then cross back into the southern portion of the Taiwan Strait around 30 hours. How much the track deviates to the southwest is highly dependent on the exact landfall location and approach angle and thus is not captured explicitly in the forecast track.
Regardless, once the system moves back over water, a west-northwest track will resume as the system comes under the steering influence of ridge again and it moves away from the influence of the terrain of Taiwan. A second landfall is forecast just prior to 72 hours along the coast of southeastern China, in the southern reaches of Fujian Province. After landfall, the system will continue to slowly track further inland through the remainder of the forecast period.
In terms of intensity, with the recent sounding from Ishikagijima showing a distinct moistening of the environment to the north, the stage is set for the system to intensify quickly prior to landfall. The limited time remaining prior to landfall (about 18 hours) will limit the peak intensity however. The peak of 105-110 knots is most likely to occur just after 12 hours, and thus is not captured in the discrete forecast points.
After landfall, the rugged terrain of Taiwan will tear the system apart, leading to a sharp and rapid weakening. At best, the system will emerge back over water as a minimal typhoon. Conditions in the Taiwan Strait will generally be favorable, but the limited time over water means that the intensity will remain steady or just slightly increase prior to the second landfall. After moving ashore, the system will rapidly weaken and potentially dissipate by the end of the forecast.
Tropical Cyclone 11W (Kirogi) – Final Warning
According to the JTWC Warning number 15…
Sustained winds were 25 knots…with gusts to near 35 knots
Animated enhanced infrared satellite imagery depicts patchy, deep convection fueled by nighttime cooling aloft flaring to the east and north of an exposed low-level circulation evident in proxy visible imagery.
The system is weakening steadily under the influence of strong southerly vertical wind shear.
Tropical depression 11W will turn westward over the next 12 to 24 hours as it follows the flow between subtropical ridging to the east and north and a deep trough to the west and south. Strong vertical wind shear driven by an upper low to the west and south of the system will drive dissipation by 48 hours.
During this period, transient deep convection associated with the circulation, supported by divergent flow aloft, will most likely flare in zones of surface convergence to the north and east of the system center. A scenario in which the system survives under the continued bombardment of vertical wind shear is difficult to fathom
>>> There’s an area of disturbed weather being referred to as Invest 96W…which is located approximately 310 NM northwest of Andersen AFB, Guam
Animated multi-spectral satellite imagery depicts a partly exposed llcc with a large band of over head convection driving to the northeast while the building convection in the southwest quadrant appears to be being sheared to the southwest.
Upper level analysis indicated 90W is in a mostly favorable environment for development with high vertical wind shear (20-30 knots), dual upper level outflow aloft to the northeast and southwest…and warm sea surface temperatures.
Global models are in good agreement that 96W will track northward, with negligible intensification expected over the next 12 to 48 hours, and then begin to dissipate.
Maximum sustained surface winds are estimated at 13 to 17 knots.
The potential for the development of a significant tropical cyclone within the next 24 hours is low.