Unusual Evolution of the Multiple Eyewall Cycles in Super Typhoon Hinnamnor (2022)

Hinnamnor was the first super typhoon in the western North Pacific basin in 2022. It had several prominent characteristics, such as rapid intensification after its formation, three eyewall cycles, and a sudden recurvature of its track. Based on multi-source observational and reanalysis datasets, two secondary eyewall formation (SEF) cycles occurred during Super Typhoon Hinnamnor’s lifetime. The first SEF happened near the time when Hinnamnor achieved its maximum intensity, and it seems that its internal dynamics dominated the SEF process after the development of shear-induced asymmetric spiral rainbands. The merger of a tropical depression with Hinnamnor led to a continuous increase in both its inner-core size and outer-core circulation, causing generation of the second SEF. It is inferred that the external and internal dynamics worked together during the second SEF process. The concentric eyewall structure maintained for approximately 84 h under the moderate vertical wind shear. Also, unique changes in intensity accompanied the two structural changes.