The cause of the occurrence of ebb or abnormal waves which are occasionally observed on the coasts is related to the spatial and temporal changes of atmospheric pressure. Because, low atmospheric pressure leads to static water level rise in a part of the marine area and high atmospheric pressure leads to static water level drop in another zone, water level throughout the entire marine area is deformed. This deformation moves as wave, sometimes amplifies on the shore. Due to the changes of atmospheric pressure, the respective small amplitude long waves propagate along the entire marine area. This type of waves can propagate through long distances and can also be amplified due to resonant effects in the enclosed basins and nearshore/offshore coastal morphology. The investigation of the amplification of the long-period waves which occurred by the spatial and temporal changes of atmospheric pressure is the one of the objectives of this study. For the different types of regular shaped basins, tests are conducted by numerical modeling solving nonlinear shallow water equations. In the tests, basins with flat, triangular, shelf, upward and downward sloping sections are simulated by using high pressure zone propagating with certain velocity (faster, equal or slower than wave velocity). The change in the sea level is calculated and compared with the theoretical outcomes.