last rain of the rainy season; final baiu rain
Refers to the heavy rain that often marks the end of the tsuyu (rainy season) in Japan, frequently accompanied by thunderstorms.
The river swelled due to the violent thunderstorm of the last rain of the rainy season.
Compound of 送り (okuri, 'sending off') and 梅雨 (tsuyu, 'rainy season'), literally 'sending-off rain', referring to the rain that marks the departure of the rainy season.