Monday, July 7, 2014

Super Typhoon Bart (1999) May Provide Insight on Neoguri Surge Potential

Super Typhoon Neoguri is a powerful typhoon packing winds of 130 kts (150 mph). The cyclone is forecast to strengthen to a category-5 typhoon, with winds reaching 140 kts (161 mph) as it tracks towards Japan. Image:NOAA

Super Typhoon Neoguri is now a well-developed tropical cyclone, packing winds of 130 knots (150 mph). The Joint Typhoon Warning Center forecasts strengthening of this typhoon, as maximum sustained winds may reach 140 knots (161 mph), while it tracks west of Okinawa. Such intensification would make Neoguri a category-5 hurricane if it were located in the Atlantic Ocean.

This typhoon is forecast to track W of Okinawa, before curving towards the NE and making landfall on the Japanese Island of Kyushu. Although Neoguri is forecast to weaken to a category-3 typhoon by landfall, storm surge correlates better with pre-landfall winds than wind speeds at landfall (Jordan and Clayson 2008; Needham and Keim 2014), so a relatively large storm surge may still occur.

Super Typhoon Neoguri is forecast to pass W of Okinawa as a category-5 tropical cyclone, then curve towards the NE, before making landfall as a major tropical cyclone on the island of Kyushu, Japan. Source:Weather Underground

Neoguri may take a similar track towards Kyushu as Super Typhoon Bart in 1999. Bart also passed west of Okinawa as a category-5 typhoon, before moving NE and making landfall on Kyushu with maximum sustained winds of 115 mph. Maximum sustained wind speeds of Bart and Neoguri may be comparable as they track west of Okinawa and move towards landfall in Kyushu.

Bart generated a 3.5 m (11.5 ft) storm surge in Yatushiro Bay (Kawai et al. 2009), which tied it for first place with Typhoon Vera in 1959 as the highest storm surge in Japan’s history, according to SCIPP's global SURGEDAT dataset. SURGEDAT has identified the location and height of 11 historical storm surge events in Japan since 1911. Unfortunately, Bart’s surge peaked near the time of a spring high tide, which further exacerbated storm surge flooding. This enabled flood waters to reach the roofs of one-story houses, while the surge claimed 12 lives (Kawai et al. 2009).

Super Typhoon Bart (1999) followed a similar track and had similar intensity as the forecast track and intensity of Super Typhoon Neoguri. Bart passed west of Okinawa as a category-5 typhoon, and then weakened to a category-3 typhoon with winds of 100 kts (115 mph) at landfall on Kyushu, Japan. Map Source: Unisys Corporation.

However, when Bart made landfall on Kyushu, it passed just west of Yatushiro Bay, enabling the storm to push a tremendous amount of water into the bay on strong southerly winds. We still do not know if Neoguri will take a similar track. If Neoguri tracks farther east, for example, it would pass to the east of Yatushiro Bay, enabling the strongest winds to blow offshore out of the bay. Therefore, while Bart's surge history may provide some general insights about surge potential from Neoguri, slight differences in typhoon track may result in large differences in surge heights at specific locations.

Super Typhoon Bart tracked just west of Yatushiro Bay, Japan, enabling strong south winds to push a 3.5 m (11.5 ft) storm surge into the Bay. This surge level is tied for Japan's highest water level in SCIPP's SURGEDAT database. Slight differences between Bart's and Neoguri's tracks may drastically change surge heights at specific locations. Image and info: Hal Needham


On island nations like Japan and the Philippines, a slight change in a typhoon track can change surge levels at a particular location dramatically. Deep inlets and bays, as well as jagged island coastlines oriented in different directions makes surge levels very localized in these countries. This was made obvious last autumn, when powerful Super Typhoon Haiyan generated a catastrophic, but localized storm surge in the Philippines. Bays and inlets near the location of landfall greatly enhanced surge levels around places like Tacloban, which observed a wall of water more typical of a tsunami than a storm surge.

Neoguri will be monitored very closely and slight changes in track forecast will likely result in large changes in storm surge heights. Coastal populations should be aware that storm surge in such situations is very localized, as one location may observe a high storm surge, but another location 20 km away may observe little or no storm surge. The most vulnerable areas to surge will be locations that are exposed to strong, onshore winds.

Jordan II, M.R., and C.A. Clayson, 2008: Evaluating the usefulness of a new set of hurricane classification indices. Monthly Weather Review, 136, 5234-5238.
Kawai, H., N. Hashimoto, and M. Yamashiro, 2009: Real-time Probabilistic Prediction of Storm Water Level at Japanese Ports. Proceedings of the Nineteenth (2009) International Offshore and Polar Engineering Conference, Osaka, Japan, June 21-26, 2009. International Society of Offshore and Polar Engineers (ISOPE).

Needham, H.F., and B.D. Keim, 2014: Correlating Storm Surge Heights with Tropical Cyclone Winds at and before Landfall. Earth Interactions, 18, 1-26.

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