Close call! Typhoon Bawu misses annual astronomical high tide by a day; SW to E coasts on alert from July 13

Taiwan is preparing for its annual astronomical high tide, which is expected to commence on July 13 and impact coastal regions in the southwest and along the east coast. Fortunately, Typhoon Bawu is predicted to move away from the island before the high tide arrives, averting a potentially disastrous combination that could lead to significant flooding.

The Central Weather Administration has outlined four major astronomical high tide periods for the year. The first two are scheduled from July 13 to 17 and August 11 to August 15, affecting the southwestern coast (from Chiayi to Pingtung) and the northeastern and eastern coasts (from Keelung to Taitung). The third period is from September 26 to September 30, impacting the western coast (from New Taipei to Changhua) and Penghu. The final high tide is expected from October 26 to October 30, affecting the western coast (Yunlin), Kinmen, and Matsu.

Astronomical high tides occur when the sun, moon, and Earth align, creating stronger gravitational forces that result in higher high tides and lower low tides. The annual high tide represents the peak tidal periods of the year, often coinciding with new or full moons near the autumnal equinox or when the moon is closest to Earth (perigee).

During these periods, coastal areas, especially low-lying regions, are at increased risk of seawater backflow and localized flooding. The weather administration cited the example of Typhoon Kimi in July 2024, which coincided with an annual astronomical high tide, causing severe flooding and seawater inundation in southwestern and northeastern coastal areas. Similar events occurred with Typhoon Vipa in late July last year and other tropical systems in August and September, prompting previous warnings from the agency.