"Maximum tidal height will likely increase, which could potentially lead to coastal flooding," she said.
In addition to bad weather, high waves, and high-speed winds, the potential flooding will coincide with the new moon phase and the perigee, she added.
The Moon is closest to the Earth at perigee, when its gravitational pull on tides also increases, she said.
Coastal flooding is forecast to impact several regions, including Natuna Islands, Riau Islands, Bangka Belitung Islands, Ternate Island, and Halmahera Island, she added.
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In addition, provinces, such as Lampung, Banten, Jakarta, West Java, Central Java, East Java, West Kalimantan, South Kalimantan, East Kalimantan, West Sulawesi, North Sulawesi, Gorontalo, West Papua, and Papua, will be affected by the phenomenon, Karnawati said.
Furthermore, it is possible that the phenomenon will also occur on December 18–22, 2021, due to the full moon phase, she added.
Coastal flooding could also be caused by the increasing intensity of extreme weather from December 2021 to February 2022 due to the Asian monsoon and the La Nina phenomenon, the BMKG head said.
The condition will become worse due to active cyclonic circulation and a cold surge in the South China Sea, which could increase wind speeds significantly to around 25 to 30 knots, she added.
It may cause wave height in the Natuna waters to reach four to six meters, she forecast.
Meanwhile, the rising wind speed in the Pacific Ocean will increase wave heights in the northern part of eastern Indonesia, she said.
"Hence, we advise the public to stay vigilant to anticipate the impact of the high waves and coastal flooding,” Karnawati added.
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