The northward propagation of the Monsoon Intraseasonal Oscillation (MISO) over the Bay of Bengal (BoB) is a vital link in the onset and precipitation variability of the Indian summer monsoon. Previous studies have demonstrated that the intraseasonal variability of upper ocean heat content (OHC) in the BoB plays a crucial preconditioning role in the northward propagation of MISOs. However, the relative contributions and physical mechanisms of local wind forcing and equatorial remote forcing across different regions remain debated. Based on a quantitative comparison across a suite of multi-dimensional model sensitivity experiments (Control, EQ, NoMISO, and NoISO), this study quantifies the contributions of local wind fields and oceanic waves to the intraseasonal variability of heat content. Results reveal that, in the boreal summer mean state, both the upper 200-m ocean heat content (OHC200) and the heat content above the 26°C isotherm (D26 OHC) exhibit strong warm centers in the northern BoB. When intraseasonal forcing is removed, the large-scale spatial pattern remains largely consistent, though the OHC magnitude slightly decreases, indicating that intraseasonal winds can modulate the background heat content. The summer total variance is most intense east of Sri Lanka (4°–10°N, 82°–88°E) and in the northwestern BoB (13°–18°N, 81°–86°E), primarily originating from the 20–100-day intraseasonal atmospheric forcing. Integrating the spatiotemporal evolution and vertical profiles of the sensitivity experiments reveals that the equatorially excited Rossby waves not only dominate the large-scale westward propagation of SLA and OHC east of Sri Lanka, but also drive the intense heaving of the subsurface (50–100 m) thermocline, allowing warm anomalies to easily penetrate the mixed and barrier layer. However, this equatorial forcing alone is insufficient to propel the thermal signals northward (as demonstrated by the EQ experiment); the synergistic forcing of the local MISO wind field is the critical factor for sustaining and developing the northward propagation of the waves (as indicated by the collapse of northward-propagating signals in the NoMISO and NoISO experiments). Meanwhile, in the northern Bay of Bengal, owing to the deep barrier layer and highly stable stratification, atmospheric heat fluxes can only warm an exceptionally shallow surface layer in the absence of strong local wind-driven vertical mixing, resulting in a vertical temperature distribution characterized by a "warm surface and cold subsurface."