Super Typhoon Meranti barrels through the Pacific and will threaten China with a major storm surge event on Wednesday night.
Note: This post was originally published on Hurricane Hal’s blog and is reposted with permission from the author.
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.
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 Forecasts, 19, 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.
Note: This post original appeared in the Natural Hazards, GIS and Disaster Management blog and is used with permission from the author.
Update: The author posted an update on the earthquake’s impacts and response on September 12, 2016.
I have nearly 35 years of professional experience in South Louisiana hydrology, including extensive work on flood risk for the Amite River Basin since 2001. First of all, kudos to The Advocate for the great work in covering the flood and flood risk information over the last two weeks. Unfortunately Mr. Robert Taylor’s letter “Flood mapping needs to change” which appeared on Monday August 29th continues to perpetuate six critical misunderstandings about flood maps and the National Flood Insurance Program (NFIP) maps. Since Mr. Taylor is the CEO of Louisiana Bankers Association, it is important to address these misunderstandings.
1. Flood maps technically belong to the local community—and the community can update the maps anytime they wish. Because local communities do not often initiate/fund updates, and because FEMA has a long backlog of requests to assist local communities in map updates along with a tight budget, we should, as a practical matter, expect many or most NFIP maps to be outdated.
2. Ironically, when local communities do initiate a map update themselves, it is almost always to REDUCE flood zones. This reduces flood insurance premiums and saves homeowners money over the short term.
3. Keep in mind the name of the maps—“Flood Insurance Rate Map.” The mapping of the flood hazard is intended to simply be sufficient to support the NFIP rate determinations. For national actuarial purposes, maps only need general regional level accuracy, not rigorous accuracy at every point on the map. Even brand new FIRMs have limitations in local accuracy given the NFIP’s goals.
4. Even the best possible flood hazard evaluations, which are done for risk assessments at very sensitive locations such as major urban areas and nuclear power plants, can have statistical uncertainties of 30 percent in estimating a 100-yr (1 percent annual chance) flood depth. That equates to three feet of uncertainty on a 100-yr flood depth of 10 feet. Professional hydrologists know that estimates of flood hazard are really “scientific guesstimates”—which is one reason why investing in map updates sometimes makes little sense.
5. Virtually every Louisianan lives in a flood hazard area. No mortgage banker should ever tell a borrower that they do not “require” flood insurance. Perhaps this is appropriate as a legal matter (and only after a very carefully worded explanation during the loan closing), but NEVER as practical or financial matter!
6. Flood risk reduction would be better served if the mortgage industry in Louisiana would urge passage of a bill by our Legislature mandating that ALL borrowers obtain flood insurance.
Our state has probably lost over a billion dollars in NFIP payments this year due to underinsurance. Unfortunately, as an earlier blog post pointed out, fixating on NFIP maps will not fix the problem of underinsurance. Fixing this fundamental problem in the how the NFIP is administered requires expanding the flood risk pool to include properties in the 500-yr (0.2% percent annual chance flood risk zone) and 1000-yr (0.1% percent annual chance flood risk zone).
Editor’s Note: An earlier version of this post appeared as a letter in The Advocate on August 29, 2016.