Land–Sea Contrast in the Diurnal Variation of Precipitation from Landfalling Tropical Cyclones

Abstract

Recent composite analysis of landfalling tropical cyclones (TCs) suggests a rain rate peak in the early morning, which contradicts the typically observed peak in convective precipitation over land seen in the late afternoon to early evening. We conducted a set of idealized simulations of TCs and analyzed observational data from TC Bebinca (2018), which stalled near the shoreline of southern China. We show a distinct land-sea contrast in the diurnal variation of TC precipitation and an 8-12 hr offset between the peak precipitation time over land compared with that over the sea in a TC that stalls at the shoreline. The highest land surface temperature and maximum low-level buoyancy during the afternoon led to peak precipitation over land at this time. However, the peak precipitation over the sea in the early morning was generated by the increase in relative humidity caused by nighttime radiative cooling and enhanced instability.Plain Language Summary Heavy rainfall associated with tropical cyclones (TCs) causes great economic loss and fatalities in coastal and inland regions worldwide. Do TCs show predictable diurnal fluctuations in rainfall, which can be valuable information for TC flooding risk or water resource management? The diurnal cycle in TC cloudiness over oceans might provide clues to this problem. Recent studies suggest an early morning peak in TC rainfall over land and sea, which seems to contradict the late afternoon to early evening peak observed over land for shower and thunderstorm activity unrelated to TCs. We found that for a TC stalled at the shoreline, peak rainfall over land lags that over sea by 8-12 hr, although the peak rainfall over sea still occurs in the early morning. Our results show, that for a landfalling TC, the offset in peak rainfall time between land and sea stems from the influence of land-sea thermal and roughness contrasts on the atmosphere.

Outer Rainband Formation on Land Ahead of Typhoon Hato (2017)

“…It developed rapidly in the afternoon hours with maximum surface heating. It is analogous to the dominant afternoon peak of rainfall on land far away from the TC center shown in previous studies (Tang et al, 2019;X. Zhang & Xu, 2021).…”

“…The afternoon-evening evolution of convective echoes corresponds to the outer rainband formation on land and its subsequent movement to offshore regions (Figures 2e and 2f). These newly developed convective systems are featured by evident afternoon growth and nighttime maintenance, which indicate the potential effects of afternoon peak of rainfall on land on the outer rainbands as discussed in recent studies (Tang et al, 2019;X. Zhang & Xu, 2021).…”

“…The sea breeze circulation is suggested to regulate the low‐level coastal convergence given the condition of landfalling TCs (Tang et al., 2019). In this study, we found that both horizontal and vertical components of the thermal contrasts contribute to the coastal convergence.…”

“…Such a process is crucial for triggering the summertime convection and TC-related convection in coastal regions (X. Chen et al, 2016;Luo et al, 2017;Tang et al, 2019). A key issue of coastal convergence formation is the dynamics of low-level winds and their differences between land and sea under TC condition.…”

Typhoon Track, Intensity, and Structure: From Theory to Prediction

“…A distinct land-sea contrast in the diurnal variation of TC precipitation is found, with peak precipitation over land occurring in the afternoon and peak precipitation over the sea occurring in the early morning (Tang et al, 2019a). For Typhoon Longwang (2005), which produced catastrophic rainfall in Fujian Province of China, the terrain and landmass near Fujian greatly affected the structure and propagation of the TC rainbands (Li et al, 2020c).…”