Tropical Instability Waves (TIWs) are the dominant source of intraseasonal variability in the central equatorial Atlantic and play an important role in the redistribution of heat in the upper ocean. Here we use multidecadal records of sea surface temperature, sea level anomaly, sea surface salinity, and near‐surface currents constructed from in situ and satellite observations to reveal a long‐term intensification of the intraseasonal variability of these variables due to an increase of TIW activity. Enhanced barotropic energy conversion from increased covariance of horizontal current fluctuations, rather than low‐frequency changes of the mean zonal currents, drives the TIW intensification. As a consequence, boreal summer cooling of tropical North Atlantic surface waters through horizontal eddy temperature advection increased by 0.03°C month−1 decade−1 during 1993–2021, a change of 74% ± 53% relative to the long‐term mean. The presented multidecadal TIW trends are strongly modulated by interannual variations like the 2021 Atlantic Niño. Plain Language Summary In the equatorial Atlantic, temperature, salinity, sea level anomaly, and ocean velocity variations on time scales of tens of days are dominated by the presence and westward passage of large‐scale Tropical Instability Waves (TIWs). Several decades of satellite and surface drifter data as well as moored velocity observations show a long‐term intensification of TIW activity in all of these variables in the tropical North Atlantic where TIWs are most pronounced. We find that increased high‐frequency flow variability, and not long‐term changes of the mean zonal current system, drives the TIW intensification. One consequence of increased Atlantic Ocean TIW activity is the corresponding intensification of the horizontal eddy temperature advection pattern in boreal summer leading to stronger cooling of surface waters north of the equator. This equates to an increase in TIW‐driven sea surface temperature cooling of 74% ± 53% in the tropical North Atlantic during the last 3 decades. The presented multidecadal TIW trends are strongly modulated by interannual variations such as the 2021 Atlantic Niño. We further explore potential large‐scale drivers of the TIW intensification, including changes in high‐frequency wind variability. Key Points In situ and satellite observations show a long‐term intensification of Tropical Instability Waves (TIWs) in the tropical North Atlantic Enhanced TIW activity is mainly due to increased barotropic instability associated with increased covariance of velocity fluctuations As a result, TIW‐driven sea surface cooling north of the equator due to eddy temperature advection has increased by 74% from 1993 to 2021