In northern Portugal, maritime pine (Pinus pinaster Ait.) stands are increasingly threatened by rising summer Vapor Pressure Deficit (VPD) and declining seasonal rainfall. Utilizing multi-decadal tree-ring width chronologies (1965–2023) from mature stands in the Tâmega River basin, this study examined how summer atmospheric aridity, seasonal precipitation, and intra-annual growth legacies interact to shape latewood formation. Our analyses demonstrate that summer VPD imposes a persistent, additive constraint on latewood width alongside summer precipitation, operating as a co-limiting driver rather than replacing rainfall controls. While lagged climate memory from prior years has attenuated in recent decades, current-year VPD sensitivity has remained remarkably stable. Crucially, tests of intra-annual growth coordination showed that the earlywood-to-latewood carry-over did not collapse under intensifying atmospheric stress. Instead, this biological legacy strengthened after 2000, acting independently of VPD and serving as the primary structural determinant of latewood growth. These findings highlight that internal growth carry-over plays a key role in buffering secondary growth against summer atmospheric aridification in Mediterranean maritime pine forests.