Consistent Pattern of Rainfall Asymmetry in Binary Tropical Cyclones.

The rainfall distribution in a tropical cyclone (TC) is affected by many factors/processes. Most of previous studies have focused on individual TCs. Little is known about the rainfall distribution in binary TCs. This study examines the rainfall distribution in binary TCs over the western North Pacific based on the observational data. When two TCs become nearby, the asymmetric component of rainfall shows an increasing trend with rainfall significantly suppressed in Quadrant IV of the TC located to the west when orienting the two TCs in the west‐east direction. The suppression becomes remarkable once the separation distance between the two TCs is within about 2,050 km. Furthermore, the convective activity in one TC is related to the deep‐layer vertical wind shear (VWS) from its companion. Rainfall is enhanced downshear‐left in a TC, consistent with a single TC embedded in an environmental VWS as found in previous studies. Plain Language Summary: The rainfall distribution in each tropical cyclone (TC) of binary‐TC systems may be more complicated than that in a single TC. Whether the rainfalls of binary TCs have some special features has not been studied before. This observational study examines the rainfall distribution in binary TCs over the western North Pacific during 2001–2020. The results show that the asymmetric component of TC rainfalls strengthened with the decreasing of the separation distance between the two TCs. If orient binary TCs in the west‐east direction, the rainfalls of the western TC were distinctly weakened in its Quadrant IV. The suppression effect cannot be neglected within 2,050‐km separation distance between binary TCs. Composite analyses indicate that the asymmetric rainfalls in one of the binary TCs were related to the deep‐layer vertical wind shear induced by its companion. The consistent pattern of rainfall asymmetry indicates a highly predictable component of rainfall distribution at vortex‐scale in binary TCs and can help improve the precipitation forecast of binary TCs. Key Points: The rainfall asymmetry increases with the decreasing separation distance between binary tropical cyclones (TCs)If the two TCs are oriented west‐east and within about 2,050 km, rainfall in the western TC is suppressed in its Quadrant IVThe asymmetric convective activity in one TC can be explained by the deep‐layer vertical wind shear from its companion [ABSTRACT FROM AUTHOR]