Current Snapshot

The Pacific Disaster Center’s (PDC Global) Friday, September 27, 2024, Tropical Cyclone Activity Report…for the Pacific Ocean, the Indian Ocean, and adjacent Seas

Current Tropical Cyclones:

Tropical Cyclone 19W (Jebi), is located about 309 NM south-southeast of Iwo To, Japan

Tropical Cyclone 20W (Krathon), is located about 370 NM northeast of Manila, Philippines

Northeast Pacific Ocean: There are no Tropical Cyclones 

Central Pacific Ocean: There are no Tropical Cyclones.

Western Pacific, Indian Ocean, and adjacent Seas:

Tropical Cyclone 19W (Jebi)

According to the JTWC warning number 7, sustained winds were 35 knots, with gusts to 45 knots.

Animated enhanced infrared (eir) satellite imagery shows that the low level circulation center (llcc) associated with tropical storm TS Jebi is now obscured, having tucked under a central dense overcast feature which has persisted for the last six hours or so. The extreme outer bands of the llcc are just visible to the northwest of the cdo feature but do not provide enough evidence to define the llcc with confidence. Cloud top temperatures in the cdo are exceeding -80c in several of the strongest hot towers. A partial pass caught the eastern portion of the center and showed a large area of 35-45 knot winds along the eastern semicircle of the circulation.

The assumed reduction in deep-layer shear is one reason why the cdo has been able to persist and expand upshear over the past six hours. The water vapor imagery also shows the beginnings of a poleward outflow channel into the eastern portion of the tutt-cell, providing an additional boost to TS 19W. The environment remains marginal, due to the likely presence of significant mid-level northwesterly shear, dry mid-level air over the northwestern portion of the system and convergent flow aloft emanating from the tutt-cell.

Track motion has slowed considerably over the last six hours as the llcc has shifted position to tucked back under the convection. However, the overall steering influence remains the ridge to the northeast. Track speeds are expected to pick up in the near-term before slowing once again as the system approaches the ridge axis around 48 hours. After 48 hours, the system turns northeastward and rapidly accelerates along the tight gradient between the ridge to the east and an approaching mid-latitude trough moving over Japan.

The current forecast track keeps TS 19W offshore but does move the track a bit closer to Japan. With this model run, the ECMWF brings TS 19W much closer to eastern Honshu, passing just 30NM offshore, brought on by a change in the placement of the ridge to the east. The GFS keeps the ridge centered further east, near 155E, with a southwest to northeast axis on the west side. The ECMWF meanwhile centers the ridge around 145E or so, with a more north to south axis on the west side.

In terms of intensity, the system is still expected to weaken slightly in the next 12 hours as the tutt-cell moves into its most unfavorable position. But as already noted, it is weakening and stretching, and will be west of TS 19W or otherwise weakened enough to limit its influence within the next 24 hours. At that point, a poleward outflow channel will open up, shear will slacken and TS 19W will start to intensify quickly.

The forecast shows the peak occurring at 72 hours, however, the actual peak is likely to occur between 72 and 96 hours with a peak between 70-80 knots. But immediately after reaching its peak, rapidly increasing shear will take its toll and the system will begin to rapidly weaken by 96 hours while also beginning extratropical transition (ett). Full transition to an extratropical low pressure area is expected no later than 120 hours.

Tropical Cyclone 20W (Krathon)

According to the JTWC warning number 4, sustained winds were 35 knots, with gusts to 45 knots.

Tropical depression 20W has rapidly organized and strengthened over the past few hours. Animated multi-spectral satellite imagery (msi) depicts an obscured low level circulationcenter (llcc), assumed to be in the center of rotating bands of convection organizing into vortical hot towers (vhts) over last couple of hours. An earlier scatterometer pass indicated the llcc was hidden under the nascent convection at that time and extrapolation of the data point provided additional clarity to the initial position estimate. The system is clearly organizing and becoming symmetrized, but another pass depicting a nascent microwave eye feature might be a bit too much. Regardless, the system has the look.

Analysis reveals a favorable environment, with very warm sea surface temperatures, high ohc, a small point source aloft over the system, with equatorward outflow being enhanced by an upper-level tutt-cell to the east.

For the next 24 hours, the primary steering mechanism for TD 20W will remain the ridge to the west, centered south of Hong Kong. The ridge however is not expected to remain stationary but rather will quickly exit stage right and move into northern Vietnam, allowing TD 20W to track southwestward through 24 hours. After 24 hours, the system moves into a weak steering pattern, caught between a large ridge complex over southern China, an extension of the ridge extending along a line from Mindanao through Guam and troughing to north over Korea.

So for the 24 hours from 24 to 48 hours, the system will very slowly drift westward as the various ridges jostle for dominance. By 48 hours, the ridge extension to the southeast is forecast to break off into a discrete anticyclone, and start moving northward while continuing to build. After 48 hours, this new ridge center will become the dominant steering influence, pushing TD 20W onto a generally northward track through the remainder of the forecast period.

Late in the forecast period, the exact position of the ridge center relative to TD 20W will have a major impact on the track forecast after 96 hours. The further east the center, the further east the track and vice versa. The current forecast keeps the center east of Taiwan but skirts the eastern coast at a relatively close range.

In terms of intensity, the system is going to enjoy favorable conditions for the bulk of the forecast period. In the near-term, intensification will be relatively slow as the system continues to consolidate and the wind field symmetrizes. The pace of intensification is expected to pick up in earnest after 36 hours, as by this point the circulation is fully formed, it is moving slowly over the highest ohc along the track and the anticyclone aloft becomes intense, with the system expected to reach typhoon strength by 48 hours, if not sooner.

But this is just setting the stage for the real fireworks, which commence at 48 hours. rapid intensification (ir) is forecast between 48 and 72 hours, followed by near-ri up to 96 hours, when the system is expected to peak at or near 115 knots. Interaction with Taiwan, and increased shear will result in modest weakening by 120 hours. One factor that may influence the peak intensity is moderate to high mid-level shear, which the GFS in particular is predicting to impact the system around 72 hours. The deterministic GFS intensity guidance picks up on this and peaks the system at about 95 knots.