“Hurricane” Hal Needham is a storm surge scientist who specializes in data-driven storm surge analysis. He is the founder and president of Marine Weather and Climate.
Super Typhoon Dujuan slammed into eastern Taiwan today as a Category 4 typhoon, with maximum sustained winds of approximately 140 mph. Dujuan made landfall slightly after 7:00 p.m. local time.
Radar and satellite loops depicted a large, powerful typhoon, which dumped tremendous rainfall on the mountainous island. As with other islands in the region, mudslides will be a major threat as heavy rains try to run off the steep terrain.
Most impacts from this storm appear to be from intense winds and heavy rain so far. Storm surge levels on Taiwan tend to be suppressed because the bathymetry — or offshore water depth — is deep, which does not allow water to pile up as efficiently. Also, Taiwan does not have as many defined bays and inlets as the Philippines, so water does not get funneled or trapped as efficiently.
Although typhoons tend to generate modest storm surge levels on Taiwan, wave heights along the coast are often tremendous. This occurs because waves “feel the bottom” of the ocean and break their energy when they reach shallow coastal waters. On islands with deep bathymetry (and usually high mountains) like Taiwan and Hawaii, most of this wave energy remains intact until the waves strike the shore.
Typhoon Doug in 1994 provides a good example of a super typhoon that generated moderate surge levels but massive waves around Taiwan. Doug produced a maximum storm surge of 5-10 feet near Lungtung Harbor, but wave heights reached 66 feet.