Tuesday, September 13, 2016

Super Typhoon Meranti Threatens China with Major Storm Surge Event

Super Typhoon Meranti barrels through the Pacific and will threaten China with a major storm surge event on Wednesday night.

In the pre-dawn hours local time Wednesday, Meranti approached the southern tip of Taiwan as a Super Typhoon with maximum sustained winds near 190 mph. This would place the storm well above the threshold for a category-5 hurricane in the Atlantic or Eastern North Pacific basins.


Super Typhoon Meranti was centered just south of Taiwan in the pre-dawn hours of Wednesday. Source: NOAA

Fortunately for Taiwan, Meranti's center of circulation is forecast to track south of the island. Nonetheless the powerful storm will inflict damage from extraordinary waves, wind and heavy rain/ mudslides.

The real concern for coastal flooding will come Wednesday night, as Meranti approaches China's coast as a Super Typhoon, with winds equivalent to a category-4 hurricane. The Joint Typhoon Warning Center predicts Meranti's maximum sustained winds will be 115 knots (132 mph) around midnight tomorrow local time, as the storm is centered just off the coast of China.

The U.S. Navy's Joint Typhoon Warning Center forecasts Super Typhoon Meranti to track towards China during the day on Wednesday. 

Meranti's storm surge potential will be a great concern in places like Xiamen, China. In 1983, Super Typhoon #4 took a similar track to Meranti and generated a 5.87-ft (1.79-m) storm surge in Xiamen (Liu 2002). The 1983 typhoon was weaker than Meranti, however, approaching the coastline with 80-knot (92 mph) winds.


Of course, typhoon size is a factor in storm surge height as well. If Meranti's size remains comparable or larger than the 1983 typhoon, and the winds remain stronger, the surge potential will be greater than in 1983, and could exceed 10 feet (3 m) in portions of coastal China. The country observes a storm surge of this height around once every three years; 15 surges exceeding 10 ft (3 m) were observed in the 50-year period from 1949 to 1998 (Tang et al. 2011).

Super Typhoon #4 in 1983 took a similar track as Meranti. Maximum sustained winds were lower than Meranti's forecast on approach to China. Source: Unisys Corporation.

Although such storm surge heights may not sound extreme by global comparison, the impacts of a coastal flood like this could be severe, given the dense coastal population in China. Even two decades ago, the 3.28 ft (1-m) coastal plain in China contains 73 million people (Han et al. 1995), enabling  low-magnitude surges to have major impacts.

Typhoon Fred in 1994 provided an excellent example of severe coastal flooding impacts in China from a moderate storm surge level. Even though the highest storm surge level only reached 8.83 ft (2.69 m) (Le, 2002), this typhoon destroyed 323 miles (520 km) of seawalls, inundated 189 towns and flooded more than 22 million people (Le, 2000).

China's densely populated coast is vulnerable to major impacts from even moderate storm surges. The city of Xiamen, pictured above, may experience a major storm surge, depending on Meranti's track. Image: realbusiness.co.uk

This should cause coastal residents to take precautions and share for a widespread storm surge from Meranti.

Coastal populations should also consider Meranti's timing when considering evacuation. Meranti's greatest surge potential will come around the time of landfall, which will be after midnight on Wednesday night. It is always harder for people to discern a flood situation during the dark of night, so it is wise for coastal residents to either evacuate or prepare for storm surge during the daylight hours on Wednesday.


REFERENCES

Han, M., J. Hou, and L. Wu, 1995: Potential impacts of sea-level rise on China’s coastal environment and cities: A national assessment, Journal of Coastal Research, 14, 79–95.

Le, K., 2000: An analysis of the recent severe storm surge disaster events in China, Nat. Hazards, 21, 215–223.

Le, K., 2002: Severe storm surge disasters and strategic measures, Mar. Forecasts, 19(1), 9–15.

Liu, J., 2002: Feature and Varied Rule of Typhoon Storm Surge along the Coast of South East China Sea. Marine Forecasts19, 1, 81-88.

Tang, L., J. M. Zhan, and Y. Z. Chen, 2011: Typhoon process and its impact on the surface circulation in the northern South China Sea, Journal of Hydrodynamics, 23(1), 95–104.

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