The sea-surface temperature (SST) tripole, with warm anomalies off the east coast of the United States and cold anomalies north of 40°N and south of 25°N, is the leading mode of interannual variability in wintertime North Atlantic SST. Its influence on northwest African rainfall is investigated by using a large-ensemble of GCM simulations. Firstly the modeled basin-scale rainfall impact is displayed, and the results suggest: in early-mid winter (November–January), a positive SST tripole causes a reduced rainfall extending from the tropical North Atlantic northeastward to Mediterranean while a negative SST causes a south-north increased rainfall across the central Atlantic from the subtropics to the midlatitude. In late winter (February–April) a positive SST tripole causes a reduced rainfall in the central Atlantic from the subtropics to the midlatitude while a negative SST tripole induces a zonal increased rainfall from the subtropics to Mediterranean. The asymmetry and seasonal dependence of the SST influence on the basin-scale rainfall is consistent with the nonlinear response of the large-scale atmospheric circulation. Under the large-scale impact background, northwest Africa regional rainfall response is also nonlinear and seasonally dependent. In early-mid winter a positive SST tripole causes reduced rainfall, while a negative SST has little effect. In late winter a negative SST tripole induces increased rainfall, while a positive tripole has little effect. A similarly large-scale asymmetric association between SST and rainfall-circulation exists in observations in late winter, while the observed seasonal dependence of this association is relatively weak. Also, a similar SST tripole association with the regional rainfall over the northwest coast of Africa exists in observations.