On the seasonal and sub‐seasonal factors influencing East China tropical cyclone landfall

Abstract

To date it has proved difficult to make seasonal forecasts of tropical cyclones, particularly for landfall and in East China specifically. This study examines sources of predictability for the number of landfalling typhoons in East China on seasonal (June-October) and sub-seasonal time scales. East China landfall count is shown to be independent of basin-scale properties of TC tracks, such the genesis location, duration, basin track direction and length, and basin total count. Large-scale environmental climate indices which are potential basin scale drivers are also shown to be largely uncorrelated with landfall prior to and throughout the season. The most important factor is the steering in the final stages to landfall. The seasonal landfall is strongly anti-correlated with the more local zonal mid-tropospheric wind field over the East China sea (r = −.61, p < .001). It is proposed that geopotential height anomalies over Korea/Japan cause anomalous easterly winds in the East China Sea and enhance landfall rates by steering typhoons onto the coast. Early, peak, and late sub-seasonal landfall counts are shown to be independent of each other yet share this predictor. This local feature may be dynamically predictable allowing a potential hybrid dynamical-statistical seasonal forecast of landfall.

Dynamical‐statistical long‐term prediction for tropical cyclone landfalls in East Asia

“… and for NEA are associated with steering flow and MJO, respectively, and those for MEA only relate to steering flow. In this regard, Sparks and Toumi (2021) showed a negligible correlation between the MEA landfall frequency and large environmental climate indices (PMM, El‐Nino, and PDO, etc.). They emphasized the importance of steering flow in landfall prediction for MEA.…”

“…The MEA vorticity patterns consist of negative vorticities from east China to the east of Japan and positive vorticities from the Indochina Peninsula to the North Pacific (Figure 5a,c). This dipole pattern causes distinctly contradicting wind anomalies in subtropics and tropics, aiding landfalls into the MEA (Sparks and Toumi, 2021). In Figure 4, the contracted WNPSH enables frequent landfall on MEA.…”

“…I G U R E 5 As in Figure 3, but for TC landfalls over MEA [Colour figure can be viewed at wileyonlinelibrary.com]tropics, aiding landfalls into the MEA(Sparks and Toumi, 2021). In Figure4, the contracted WNPSH enables frequent landfall on MEA.…”