This Monday, September 28, 2026, coastal areas may see unusually high tides due to a mix of natural and weather-related factors. The tide coefficient, a measure used to predict the height of tides, is expected to reach 99, which is considered high because it surpasses the 90 threshold on a scale that ranges from 20 to 120. This high coefficient is caused by the alignment of the Sun, Moon, and Earth during the September equinoxes, which increases the gravitational pull on the oceans. Another period of high tides is forecast around October 27, with a coefficient of 100 recorded in Brest, a coastal city in France. The tide coefficient alone does not account for weather conditions, which can significantly affect sea levels. One such factor is the inverse barometer effect, where lower atmospheric pressure causes sea levels to rise. A drop in pressure by 1 hectopascal (a unit of pressure) can raise sea levels by about 1 centimeter. For example, a low-pressure system with a reading of 980 hPa—35 hPa below the average of 1015 hPa—could cause an additional 35 centimeters of sea level rise. Similarly, a depression with a pressure drop of 30 hectopascals could lead to an increase of about 30 centimeters. When a high tide coefficient, low atmospheric pressure, and strong waves occur together, the result can be water levels that exceed typical predictions. This combination has caused notable flooding events along the French coast in recent years. The greatest risk happens when these factors align, leading to unexpectedly high water levels that can threaten coastal communities. Areas such as Vendée and Charente, in western France, may experience especially dramatic tidal ranges when the coefficient exceeds 110. High tides attract many people who enjoy activities like wading fishing and water sports along the coasts of the English Channel and the Atlantic. However, it is crucial to follow official forecasts from SHOM, France’s hydrographic and oceanographic service, and to monitor local weather conditions, especially changes in atmospheric pressure, to prepare for potential flooding.