UPDATE: There are significant changes (as of Friday mid day Middle America Time) in the track and strength of the storm, mostly good news for china. See here for updates.
A large typhoon (hurricane) is heading for China and is expected to make landfall in the vicinity of Shanghai. The image above is from the Japan Meteorological agency, and the image below is from JAM via Jeff Masters Blog.
Apparently Chan-hom will make landfall in a region that very rarely sees typhoons. Chan-hom will be, according to Masters,
… one of the strongest typhoons on record for a portion of the country unused to strong typhoons. Of particular concern is Chan-hom’s storm surge, which has the potential to bring the highest water levels ever observed into Shanghai, China’s most populous city, with 23 million people in the metro area.
This is all going to happen Saturday US time, in the wee hours of the morning, but PM locally. The storm, now a category 4, will likely be a category 2 at the time of landfall, which is still a problem.
The region has real tides, so a storm surge of several feet during low tide may be not such a big deal, while a storm surge on top of high tide could be devastating. In 1956 a storm came through with a nearly 6 foot storm surge but the normally 7+ foot tide was not high. In 1997, Winnie, a mere Category 1, struck near Shanghai. According to Jeff Masters,
the storm surge from Winnie was only 5.5″ (14 cm) below the top of the 19.2-foot (5.86 meter) Suzhou Creek floodgate that protects downtown Shanghai on the Huangpu River, which flows through the center of town. This floodwall was rated to protect against a 1-in-200 year flood, and was overtopped by about one foot (30 cm) along a 8.5 mile (13.7 km) section inland from the downtown area, flooding over 400 homes
The tied, therefore, will make a huge difference, and it is probably too early to say much about the co-occurrence of high tide and Chan-hom’s landfall.
Jeff has a LOT more on this storm and several related issues such as sea level rise in the area at his post.