Typhoon Chanthu (2021)

Map plotting the storm's track and intensity, according to the Saffir–Simpson scale

Map key

Saffir–Simpson scale

  Tropical depression (≤38 mph, ≤62 km/h)
  Tropical storm (39–73 mph, 63–118 km/h)
  Category 1 (74–95 mph, 119–153 km/h)
  Category 2 (96–110 mph, 154–177 km/h)
  Category 3 (111–129 mph, 178–208 km/h)
  Category 4 (130–156 mph, 209–251 km/h)
  Category 5 (≥157 mph, ≥252 km/h)
  Unknown

Storm type

Tropical cyclone

Subtropical cyclone

Extratropical cyclone, remnant low, tropical disturbance, or monsoon depression

At 06:00 UTC on September 5, the JTWC began to monitor an area of disturbed weather that had formed 446 nmi (513 mi; 826 km) from Legazpi, Philippines.[3] At 18:00 UTC the same day, the JMA declared the system a tropical depression.[4] Later in the day, the JTWC issued a Tropical Cyclone Formation Alert as the system's low-level circulation center and its surrounding convection had improved significantly in organization.[5] At 09:00 UTC the next day, the JTWC upgraded the disturbance to a tropical depression, designating as 19W.[6] At 21:00 UTC, the JTWC upgraded it to a tropical storm; they also noted the formation of an eye-like feature on satellite images.[7] The JMA later did the same at 00:00 UTC of September 7, providing the name Chanthu.[8] At 09:30 UTC, the PAGASA reported that Chanthu entered the Philippine Area of Responsibility (PAR) and was named Kiko.[9] At 12:00 UTC, as satellite based intensity estimates from the Dvorak technique increased, the JMA upgraded Chanthu to a severe tropical storm.[10] At the same moment, Chanthu started rapid intensification as it quickly became a Category 1-equivalent typhoon. Satellite imagery indicate a development of a vertical hot tower over its center, with microwave imagery indicating that it had developed a very small eye feature.[11][12] At 15:00 UTC, it had become a Category 2-equivalent typhoon, as it continued explosive intensification. A pinhole eye, a typical sign of a rapidly intensifying tropical cyclone, had developed by that time.[13] Six hours later, the typhoon reached Category 4 status, with one-minute sustained wind speeds of 125 kn (230 km/h; 145 mph).[14] By the next day, at 09:00 UTC, Chanthu had reached Category 5-equivalent intensity, developing a 5 nmi (10 km; 5 mi)-wide eye which was by very intense convection,[15][16] making it the second super typhoon of the year and marking the storm's initial peak intensity.

Tropical Storm Conson (left) and Typhoon Chanthu at its initial peak. (right) on September 8.

After reaching its initial peak, Chanthu was downgraded to a Category 4-equivalent super typhoon at 09:00 UTC on September 9, as its highly compact eye started to become cloud-filled, indicating the start of an eyewall replacement cycle.[17] However, shortly after, Chanthu quickly re-intensified into a Category 5-equivalent super typhoon yet again at 09:00 UTC that day, as its eye became clear again.[18] On 05:00 PhST of September 11 (21:00 UTC of September 10), the PAGASA reported that Chanthu passed to the east of the Babuyan Islands;[19] at 08:30 PhST (00:30 UTC), Chanthu made landfall in Ivana, Batanes as a Category 5 super typhoon with 1-minute sustained winds of 270 km/h (165 mph) as the storm began to weaken slightly.[20][21] At 15:00 UTC on September 11, Chanthu weakened to a Category 4-equivalent typhoon as it continued to move northward because of the presence of dry air.[22] It was further downgraded to a Category 3-equivalent typhoon by the JTWC on September 12 at 03:00 UTC as it moved towards the east coast of Taiwan, experiencing multiple eyewall replacement cycles, increasing wind shear and dry, stable air.[23] Three hours later, the PAGASA issued its last bulletin on the system since it had exited the PAR.[24] At 15:00 UTC, Chanthu weakened to a Category 2-equivalent typhoon as the dry air started to hamper the typhoon's convective structure. According to satellite imagery, the low-level circulation center had become ill-defined and the eye started to collapse.[25] The weakening trend of Chanthu continued as it moved further northward towards the Korean Peninsula because of increasing wind shear, dry air and cool sea surface temperatures.[26][27] At 09:00 UTC of September 13, Chanthu further weakened into a Category 1 typhoon as it moved further north towards Shanghai.[28] By 15:00 UTC, the eye of Chanthu had completely collapsed.[29] Chanthu remained quasi-stationary near Shanghai because of weak steering flow.[30][31] At 06:00 UTC the next day, the JMA downgraded Chanthu to a severe tropical storm as it moved southeastward.[32] Three hours later, the JTWC downgraded Chanthu to a tropical storm as its low-level circulation became partially exposed, with convection only remaining to the north and west.[33] At 12:00 UTC, the JMA further downgraded it to a tropical storm as it slowly moved south-eastward towards Japan.[34] At 00:00 UTC on September 15, due to decreasing wind shear and marginally favorable sea surface temperatures, Chanthu re-strengthened and was re-classified as a severe tropical storm that day.[35] After continued slow movement, on September 17 at 09:00 UTC, Chanthu made landfall near itsuki, Nagasaki in Japan.[36] It continued to move northward as it moved through the rugged Japanese islands, causing it to weaken significantly.[37] This caused the JMA to downgrade it to a tropical storm at 12:00 UTC.[38] At 21:00 UTC, the JTWC downgraded it to a tropical depression as it rapidly collapsed because of the rugged terrain; it was also undergoing extratropical transition.[39] On September 18 at 08:00 UTC, the JTWC issued its final warning for the system, as the system became extratropical.[40] Afterward, Chanthu's remnant continued moving eastward and then curved southward, before dissipating on September 20.

In the Philippines, 415 people were evacuated.[41] As Chanthu came closer towards Luzon, the PAGASA issued Signal No. 1 warnings over Cagayan and Isabela provinces.[42] At 23:00 PhST of September 9, the PAGASA raised a Signal No. 2 warning over the northeastern portion of Cagayan and eastern portion of Babuyan and Signal No. 1 was further extended over Batanes, rest of Cagayan and Babuyan, northeastern portion of Apayao and eastern portion of Isabela.[43] At 05:00 PhST the next day, a Signal No. 3 warning was raised over Santa Ana, Cagayan.[44]

At 05:30 NST of September 10, the Central Weather Bureau in Taiwan issued a sea warning,[45] which was followed by a land warning for Super Typhoon Chanthu.[46] At 17:00 PhST, the PAGASA raised a Signal No. 4 warning over the northeastern portion of Babuyan Islands.[47] President of Taiwan, Tsai Ing-wen advised people to stay indoors due to torrential rain and strong winds.[41] Transportation in Taiwan was also halted, with over 100 flights,[48] trains and 46 ferries to Matsu and other surrounding islands cancelled.[41] Around 2,000 people in landslide-prone areas in the eastern portions of Hualien County were evacuated, and sections of highway in the area were closed by authorities. The Taiwanese Defence Ministry put 31,000 troops on standby.[48]

The storm shut down both China's Shanghai Port and the Port of Ningbo-Zhoushan, the world's largest port by cargo throughput, between September 12–14. About 86 vessels were left waiting outside the ports.[49]

• Weather of 2021
• Tropical cyclones in 2021
• Typhoon Zeb (1998)
• Typhoon Nida (2004)
• Typhoon Noul (2015)
• Typhoon Meranti
• Typhoon Mangkhut
• Typhoon Nanmadol (2011)
• Typhoon Doksuri (2023)

Wikimedia Commons has media related to Typhoon Chanthu (2021).

• JMA General Information of Typhoon Chanthu (2114) from Digital Typhoon
• JTWC Best Track Data of Super Typhoon 19W (Chanthu)
• 19W.CHANTHU from the U.S. Naval Research Laboratory