expression, noun
rainy spells just before the rainy season
Refers to the intermittent rain that falls in the period leading up to the official start of the rainy season (tsuyu) in Japan, typically in late May to early June.
今年は梅雨の走りが早くて、もう雨の日が続いている。
This year the pre-rainy-season rains came early, and we've already had a string of rainy days.
梅雨の走りで洗濯物が乾かない。
Because of the pre-rainy-season rain, the laundry won't dry.
Compound of 梅雨 (tsuyu, 'rainy season') + の (possessive particle) + 走り (hashiri, 'first signs, beginning'). The word 走り derives from the verb 走る (hashiru, 'to run'), metaphorically extended to mean the first appearance or onset of something.