Abstract: MHWs (Marine heatwaves) are extreme high-temperature events in the ocean that can have substantial impacts on marine environments and ecosystems. This study utilized daily SST (sea surface temperature) data from NOAA (National Oceanic and Atmospheric Administration’s) OISST V2 dataset, atmospheric reanalysis data from ERA5 provided by the European Centre for Medium-Range Weather Forecasts, and ocean reanalysis data from NCEP (National Centers for Environmental Prediction). Using these datasets, this study analyzed the spatiotemporal characteristics of the record-breaking MHW events in the subtropical northeastern Atlantic (SNA) during spring 2023. The results indicate that the North Atlantic experienced an unprecedented rise in SST during spring 2023, with the SNA emerging as a prominent hotspot. Diagnostic analysis of the upper-ocean mixed-layer heat budget reveals that, throughout the MHW events, net surface heat flux played a dominant role in sea–atmosphere energy exchange at each stage. The SNA endured over 90 days of MHW conditions, presenting two major events with distinct initiation, peak, and decline phases. Variations in their intensity and spatial extent were regulated by a positive wind–evaporation–SST feedback mechanism. During the initiation phase, an anomalous low-pressure system reduced surface wind speed, seawater evaporation, and latent heat loss, resulting in an anomalous downward net heat flux and ocean warming. During the peak phase, under the influence of an anomalous high-pressure system, further reductions in wind speed and suppressed evaporation promoted continued SST increases and intensified the MHWs. During the decline phase, strengthened surface winds enhanced evaporation, consequently decreasing SST and ultimately terminating the events. In addition, the formation and maintenance of these MHW events were closely related to an eastward-propagating Rossby wave originating over the Pacific Ocean. During the decline phase of the MHWs, anomalously warm SSTs triggered an eastward-propagating Rossby wave across Eurasia, causing anomalously low temperatures in eastern China.