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Abstract Seasonal predictions of tropical cyclone (TC) landfalls are challenging because seasonal landfall count not only depends on the number and spatial distribution of TC genesis, but also whether those TCs are steered toward land or not. Past studies have separately examined genesis and landfall as a function of large-scale ocean and atmospheric environmental conditions. Here, we introduce a practical statistical framework for estimating the seasonal count of TC landfalls as the product of a Poisson model for seasonal TC genesis and a logistic model for landfall probability. We compute spatial variations in TC landfall and genesis by decomposing TC activity in the western North Pacific (WNP) basin into 10° × 10° bins, then identify coherent regions where El Niño–Southern Oscillation (ENSO) and the western extent of the Pacific subtropical high (WPSH) have significant influences on seasonal landfall count. Our framework shows that ENSO and the WPSH are weakly related to basinwide landfalls but strongly related to regional genesis and landfall probability. ENSO modulates the zonal distribution of TC genesis, consistent with past work, whereas the WPSH modulates the meridional distribution of landfall probability due to variations in steering flow associated with the Pacific subtropical high. These spatial patterns result in four coherent subregions of the WNP basin that define seasonal landfall variations: landfall count increases in the southwestern WNP during a positive WPSH and La Niña, the south-central WNP during a positive WPSH and El Niño, the eastern WNP during a negative WPSH and El Niño, and the northern WNP during a negative WPSH and La Niña.
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Climate Projection of Tropical Cyclone Lifetime in the Western North Pacific Basin
Abstract In this study, the potential changes in tropical cyclone (TC) lifetime in the western North Pacific basin are examined for different future climates. Using homogeneous 9-km-resolution dynamical downscaling with the Weather Research and Forecasting (WRF) Model, we show that TC-averaged lifetime displays insignificant change under both low and high greenhouse gas concentration scenarios. However, more noticeable changes in the tails of TC lifetime statistics are captured in our downscaling simulations, with more frequent long-lived TCs (lifetime of 8–11 days) and less short-lived TCs (lifetime of 3–5 days). Unlike present-day simulations, it is found that the correlation between TC lifetime and the Niño index is relatively weak and insignificant in all future downscaling simulations, thus offering little explanation for these changes in TC lifetime statistics based on El Niño–Southern Oscillation. More detailed analyses of TC track distribution in the western North Pacific basin reveal, nevertheless, a noticeable shift of TC track patterns toward the end of the twenty-first century. Such a change in TC track climatology results in an overall longer duration of TCs over the open ocean, which is consistent across future scenarios and periods examined in this study. This shift in the TC track pattern is ultimately linked to changes in the western North Pacific subtropical high, which retreats to the south during July and to the east during August–September. The results obtained in this study provide new insights into how large-scale circulations can affect TC lifetime in the western North Pacific basin in warmer climates. Significance StatementUsing high-resolution dynamical downscaling with the Weather Research and Forecasting (WRF) Model under low- and high-emission scenarios, this study shows that the basin-averaged tropical cyclone (TC) lifetime in the western North Pacific (WNP) basin has no noticeable change under both warmer climate scenarios, despite an overall increase in TC maximum intensity. However, the tails of the TC lifetime distribution display significant changes, with more long-lived (6–20 days) TCs but less short-lived (3–5 days) TCs in the future. These changes in TC lifetime statistics are caused by the shift of the North Pacific subtropical high, which alters large-scale steering flows and TC track patterns. These results help explain why previous studies on TC lifetime projections have been inconclusive in the WNP basin and provide new insights into how large-scale circulations can modulate TC lifetime in a warmer climate.
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- Award ID(s):
- 2309929
- PAR ID:
- 10558859
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Climate
- Volume:
- 38
- Issue:
- 1
- ISSN:
- 0894-8755
- Format(s):
- Medium: X Size: p. 181-201
- Size(s):
- p. 181-201
- Sponsoring Org:
- National Science Foundation
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