Environmental Conditions Determining the Timing of the Lifetime Maximum Intensity of Tropical Cyclones over the Western North Pacific and Their Frequency of Occurrence |
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| Authors: | QIN Xiao-hao YAMAGUCHI Munehiko USUI Norihisa and HIROSE Nariaki |
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| Institution: | State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029 China,Department of Applied Meteorology, Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Ibaraki 305-0052 Japan,Department of Atmosphere, Ocean, and Earth System Modeling Research, Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Ibaraki 305-0052 Japan and Department of Atmosphere, Ocean, and Earth System Modeling Research, Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Ibaraki 305-0052 Japan |
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| Abstract: | Environmental conditions determining the timing of the lifetime maximum intensities of tropical cyclones (TCs) are investigated for the TCs over the western North Pacific during the period 2008-2017. The results show that the land controls the timings of the lifetime maximum intensities in 42% of the TCs over this basin, indicating that accurate track forecasts are beneficial for TC intensity forecasts. With respect to other TCs that are not affected by the land (i.e., Ocean-TCs), the timings of their lifetime maximum intensities are determined by multiple oceanic factors. In particular, interactions between TCs and cold-core eddies occur in a large proportion (nearly 60%) of Ocean-TCs at or shortly after the times of their lifetime maximum intensities, especially in strong TCs (categories 4 and 5), suggesting that a consideration of the above interactions is necessary for improving TC intensity forecasting skills. In addition, unfavorable oceanic heat content conditions become common as the latitude increases over 25°N, influencing half of the Ocean-TCs. Strong vertical wind shear contributes detrimentally to the atmospheric environment in 17% of the TCs over this basin, especially in moderate and weak TCs. In contrast, neither the maximum potential intensity nor the humidity in the middle level of the atmosphere plays dominant roles when TCs turn from their peak intensities to weakening. |
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| Keywords: | environmental conditions lifetime maximum intensity tropical cyclones frequency of occurrence |
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