Monsoon Tail Rainbands and Tropical Cyclogenesis in the Western North Pacific: Climatology and a Typhoon Jebi (2018) Case Study.
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| Title: | Monsoon Tail Rainbands and Tropical Cyclogenesis in the Western North Pacific: Climatology and a Typhoon Jebi (2018) Case Study. |
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| Authors: | Nam, Chaehyeon C.1 ccnam@fsu.edu, Bell, Michael M.2 |
| Source: | Journal of Climate. May2026, Vol. 39 Issue 9, p1-17. 17p. |
| Subjects: | Tropical cyclones, Vertical wind shear, Typhoons, Free convection |
| Geographic Terms: | North Pacific Ocean |
| Abstract: | During the Propagation of Intra-Seasonal Tropical Oscillations (PISTON) field campaign in the summers of 2018 and 2019 over the western North Pacific (WNP), many tropical cyclones (TCs) exhibited an elongated rainband in the southwestern (SW) quadrant, typically located 500–1,000 km from the storm center. We refer to this feature as the "monsoon tail (MT)," hypothesizing that it forms through interactions between the TC circulation and monsoon southwesterlies. A notable case was Typhoon Jebi (2018), where a trailing rainband detached from the main circulation and persisted as widespread convection. This system developed a closed low-level circulation and was designated as Invest 98W by the Joint Typhoon Warning Center but ultimately failed to undergo tropical cyclogenesis (TCG). Motivated by these observations, we conducted a 40-year climatological analysis and a case study of Jebi and Invest 98W. We found that approximately 80% of WNP TCs exhibited at least one MT event under a moderate threshold (5,000 km2 of area, 6 hours of duration). Convective asymmetry in the SW quadrant was most strongly correlated with zonal wind shear, while low-level monsoonal flow and thermodynamic factors played secondary roles. Vertical wind shear helped organize asymmetric convection downshear, enabling detached MT structures to resemble incipient disturbances. This dual role of VWS and the preexisting TC circulation—enhancing vorticity and moisture while imposing hostile shear—was evident not only in the Invest 98W case but also in the climatological analysis using its location as an illustrative example. These findings highlight how MT rainbands may exhibit developmental potential yet remain inhibited from TCG by environmental shear from the parent TC. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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| Abstract: | During the Propagation of Intra-Seasonal Tropical Oscillations (PISTON) field campaign in the summers of 2018 and 2019 over the western North Pacific (WNP), many tropical cyclones (TCs) exhibited an elongated rainband in the southwestern (SW) quadrant, typically located 500–1,000 km from the storm center. We refer to this feature as the "monsoon tail (MT)," hypothesizing that it forms through interactions between the TC circulation and monsoon southwesterlies. A notable case was Typhoon Jebi (2018), where a trailing rainband detached from the main circulation and persisted as widespread convection. This system developed a closed low-level circulation and was designated as Invest 98W by the Joint Typhoon Warning Center but ultimately failed to undergo tropical cyclogenesis (TCG). Motivated by these observations, we conducted a 40-year climatological analysis and a case study of Jebi and Invest 98W. We found that approximately 80% of WNP TCs exhibited at least one MT event under a moderate threshold (5,000 km2 of area, 6 hours of duration). Convective asymmetry in the SW quadrant was most strongly correlated with zonal wind shear, while low-level monsoonal flow and thermodynamic factors played secondary roles. Vertical wind shear helped organize asymmetric convection downshear, enabling detached MT structures to resemble incipient disturbances. This dual role of VWS and the preexisting TC circulation—enhancing vorticity and moisture while imposing hostile shear—was evident not only in the Invest 98W case but also in the climatological analysis using its location as an illustrative example. These findings highlight how MT rainbands may exhibit developmental potential yet remain inhibited from TCG by environmental shear from the parent TC. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 08948755 |
| DOI: | 10.1175/JCLI-D-25-0092.1 |
