Does initial soil moisture condition affect poleward-moving tropical cyclone forecasts?

Abstract

Soil moisture (SM) is a critical land surface variable that modulates land–atmosphere interactions through the partitioning of surface energy and moisture fluxes. This study examines the sensitivity of forecasts of poleward-moving, landfalling tropical cyclones (TCs) to initial SM condition. We conducted Weather Research and Forecasting (WRF) model experiments for three recent TCs that affected South Korea using initial SM from the Global Land Data Assimilation System (GLDAS) Noah v2.1 and the European Centre for Medium-Range Weather Forecasts Reanalysis v5 (ERA5), hereafter referred to as the GL and ERA5 runs, respectively. The ERA5 run maintained positive SM differences relative to the GL run over a trough-development region spanning Northeast China and adjacent Mongolia, although the differences were spatially heterogeneous across the broader land domain. The GL runs had smaller landfall-period track errors in the three selected cases, with the clearest separation for Hinnamnor. During the later forecast period, the ERA5 run produced a westward-to-northwestward track displacement relative to the GL run, accompanied by a deeper, more westward-displaced mid-latitude trough and a modified upper-level steering environment. Process-oriented diagnostics indicate a physically consistent sequence linking persistent differences originating from the SM initialization to surface flux and moist thermodynamic responses, stronger ascent, trough modification, steering flow differences, and the simulated TC track response. These results demonstrate sensitivity of medium-range mid-latitude circulation and poleward-moving TC track forecasts to the prescribed initial SM condition.