Addressing coastal erosion is a long-standing issue that has been the focus of extensive research in recent years. Other fields of geosciences demand the determination of the Earth’s gravity field and geoid with very high accuracy, on the order of ±1 cm for wavelengths of approximately 10 km along the coastal front, in order to integrate with other Earth observation data, whether satellite-based or terrestrial. Satellite altimetry has offered unprecedented opportunities to monitor sea level variations and study the marine gravity field over the past decades. This study presents the results of a multi-year analysis of satellite altimetry data, focusing on the Aegean Sea, Greece, employing both classical Low-Resolution Mode (LRM) and SAR/SARin data. Two main analysis methods are employed as tools to identify the primary modes of sea level variation and trends, i.e., Empirical Orthogonal Function/Principal Component Analysis (EOF/PCA) and Wavelet Transform. Based on these approaches, annual and semi-annual patterns are identified in the altimetry time series, while the trend of sea level changes is determined. Two scenarios, based on 50-year and 100-year simulations, are presented, highlighting the areas in the North Aegean Sea that are most susceptible to flooding and, consequently, more vulnerable to erosion due to sea level forcing.