September marks the peak of the tropical season and busy times for ship routing. This is especially true in NW Pacific when multiple tropical systems threaten the eastern Asian ports and major shipping lanes bringing extra challenges.
Himwari Image from 9 Sept showing Tropical Storm (18W) Conson and Super Typhoon (19W) Canthu over the NW Pacific.
Emerging in the South China Sea (SCS) late on September 8th, Tropical Storm(TS) 18W (Conson) became disorganized for a time over the Philippines, but continued in a general westward track along 16N over the South China Sea headed to central Vietnam. The track for TS Conson was not well forecast by the global models due to weak steering flow over the northern SCS. The models kept trying to recurve the track to the north or northwest but this never came to fruition as shown in Fig. 1 with Conson going ashore close to 16N near Danang, Vietnam around 13/00Z Sept. It provides a good example of the complexity for routing vessels safely and keeping an optimized route.
Fig 1. Left: JTWC forecast from 08/12Z (Source: JTWC) Centre: GEFS ensembles for 08/18Z displaying large uncertainty and expected northward curve ( Source weathernerds.org) Right: JTWC final warning 12/21Z
At the same time, on the other side of the Philippines, Super Typhoon (ST) 19W (Chanthu) also roared into life to add to the complexity in the NW Pacific. Chanthu first became a tropical depression in the early afternoon of 6th September and underwent rapid intensification to reach ST status within 48 hours and reached a peak intensity of 155kts on 10th September, making this system the strongest of the season so far. Initially the global models had the system tracking northwest over the Luzon Strait but later model runs from the 8th September curved the track more northward to east of Taiwan and then continue north to be off of Shanghai as depicted in Fig. 2. As the global models had difficulty in seeking track consensus early on there was low confidence in the extended forecast track over this period, which posed many challenges for routing decisions in this very busy region of the world.
Fig 2. Shift in forecast track trend for TS Chanthu over 24 hour period 8-9 September 2021 by JTWC (Source JTWC).
By example, figure 3 below shows a route which seemed optimized on the 8th September but which needed to be significantly modified on the 9th September. The route displayed in green (left image) was sent to a client vessel 08/00Z Sept. Note the eastward deviation from the most direct route to Singapore remained west of Okinawa. The right image was the amended route evaluation sent to the same client using model data 36 hours later. Due to the significant eastward trend in the official forecast as observed in Figure 2, the vessel was recommended to then transit via east of Okinawa to maintain a safe distance away from Chanthu.
Fig 3. Left: GFS wind date with recommended route and JTWC forecast cone superimposed for 11/00Z Sept and Right: Route modified 24 hours later.
Such scenarios require 24/7 very close monitoring by experts in the knowledge that safety comes first.
Stay safe and connected.