By PDC’s Senior Weather
Specialist Glenn James
The Pacific Disaster Center’s (PDC Global) Tuesday, August 15, 2023, Tropical Cyclone Activity Report…for the Pacific Ocean, the Indian Ocean, and adjacent Seas
Current Tropical Cyclones:
Tropical Cyclone 07E (Fernanda)…is located about 1000 miles west-southwest of the southern tip of Baja California
Tropical Cyclone 08E (Greg)…is located about 725 miles southeast of Hilo, Hawaii
Tropical Cyclone 05E (Dora)…is located about 329 NM north-northeast of Wake Island – Final Warning
Tropical Cyclone 07W (Lan)…is located approximately 266 NM northwest of Yokosuka, Japan
Northeast Pacific Ocean:
Tropical Cyclone 07E (Fernanda)
FERNANDA CONTINUES WEAKENING AS IT MOVES OVER THE OPEN PACIFIC WATERS
According to the NHC advisory number 14…
Fernanda is moving toward the west near 14 mph (22 km/h) and a general westward motion is expected to continue for the next few days.
Maximum sustained winds have decreased to near 90 mph (150 km/h) with higher gusts. Rapid weakening is forecast during the next 48 hours and Fernanda is likely to become a post-tropical remnant low on Thursday.
Hurricane-force winds extend outward up to 35 miles (55 km) from the center and tropical-storm-force winds extend outward up to 90 miles (150 km).
>>>Off the coast of southern and southwestern Mexico…
Showers and thunderstorms are continuing to show signs of organization in association with a broad area of low pressure located a few hundred miles south of Acapulco, Mexico.
Environmental conditions appear conducive for continued development, and a tropical depression or tropical storm is anticipated to form within the next day or so.
The system is expected to move west-northwestward to northwestward, roughly parallel to the coast of southwestern Mexico and the Baja California peninsula during the next several days.
* Formation chance through 48 hours…high…90 percent
* Formation chance through 7 days…high…90 percent
>>> South of Central America and Southern Mexico…
An area of low pressure could form south of the Gulf of Tehuantepec over the weekend.
Some gradual development of this system is possible thereafter while it moves generally west-northwestward.
* Formation chance through 48 hours…low…near 0 percent
* Formation chance through 7 days…low…20 percent
Central Pacific Ocean:
Tropical Cyclone 08E (Greg)
TROPICAL STORM GREG CONTINUES MOVING WESTWARD
According to the CPHC advisory number 9…
Greg is moving toward the west near 14 mph (22 km/h). A gradual turn toward the west-northwest is expected tonight. Greg is forecast to turn toward the west Wednesday night and Thursday, then shift toward the west-southwest late Thursday and Friday.
Maximum sustained winds are near 50 mph (85 km/h) with higher gusts. Some strengthening is possible into Wednesday, followed by weakening Thursday and Friday.
Tropical-storm-force winds extend outward up to 70 miles (110 km)
from the center.
Western Pacific, Indian Ocean and adjacent Seas:
Tropical Cyclone 05E (Dora) – Final Warning
According to the JTWC warning number 63…
Sustained winds are 25 knots…with gusts to 35 knots
Animated enhanced infrared satellite imagery depicts a partially exposed low level circulation center (llcc) with flaring convection being sheared to the northeast.
TD 05E (Dora) is forecast to track generally poleward under the steering influence of the low to mid-level subtropical ridge (str) to the northeast. the primary deterrent to any significant intensification is a tropical upper-tropospheric trough (tutt) cell located on the northwestern periphery of the system.
As 05E tracks poleward, the subsidence from the tutt combined with moderate environmental shear values will continue to eat away at the western periphery of the circulation. At the same time, the eastern portion of the circulation is thriving in the enhanced outflow and lower shear provided by the same tutt cell.
This is creating a unique situation wherein the two sides of the circulation will be holding each other in near steady state as the whole circulation propagates poleward.
By 36 hours, the circulation will continue to slowly succumb to the persistent shear and subsidence aloft, gradually spinning down and eventually dissipating by 72 hours.
Tropical Cyclone 07W (Lan)
According to the JTWC Warning number 34…
Sustained winds were 45 knots…with gusts to near 55 knots
Animated enhanced infrared satellite imagery depicts a deteriorating and asymmetric web of convective bands with the low level circulation center decoupled from the upper level circulation center. Without the luxury of new microwave imagery, animated radar imagery was the primary localizing tool.
A large donut-like structure is still evident as the circulation emerges back over open water. A partial soil moisture active passive pass revealed the leading edge of the circulation has weakened to around 45 knots with a majority of the primary wind field at 35-40 knots.
Having recently entered the warm waters of the Sea of Japan, TS 07W (Lan) is forecast to proceed generally poleward. As 07W tracks northward, steadily improving outflow aloft will fight to overcome gradually increasing vertical wind shear values. The result of this battle will almost certainly be anticlimactic, 07W will likely only maintain most of its intensity through 24 hours.
The current JTWC forecast philosophy is one of gradual decline due to the increasing shear values beyond 36 hours. As the system passes the 44th parallel, 07W will begin to interact with a strong baroclinic zone as it further increases its poleward track speed, thereby initiating extra-tropical transition (ett).
By 120 hours, now well into the Sea of Okhotsk, 07W will lose its last remaining tropical characteristics and complete ett just before its eventual dissipation.