Severe Weather in Japan

Tornadoes form by three basic steps; step 1 is the first object that forms is a rotating body of air at the ground and this occurs because of vertical wind shear. The higher that you are in altitude, the higher the wind speeds will get. Step 2 happens when horizontal rotating air is lifted off the ground by the updraft of a thunderstorm. Once this horizontal rotating mass is lifted into a vertical position it is considered a mesocyclone. By step 3 the mesocyclone is fully developed in the updraft of the storm. If a tornado develops it comes from the wall cloud located in the lower part of the cloud. In the United States, tornadoes tend to travel southwest to northeast (west to east) in the United States. This is because of an increased frequency of certain tornado producing weather patterns. Wind blows across the United States from west to east, so the tornadoes are going to follow the thunderstorms and winds across the country. In Japan, tornadoes do occur often but it is far less devastating than parts of the United States. Annually, an average of 20.5 tornadoes occur in Japan. However, only 1 tornado prior to 2000 made it to F4 on the Fujita Scale, and since 1960, no tornado has killed more than 10 people in Japan-even despite its dense population. In the United States, 1,200 tornadoes occur annually.

http://www.wunderground.com/blog/weatherhistorian/f5ef5s-and-the-worlds-deadliest-tornadoes

According to this map, Japan is between low and moderate risk of tornadoes, and it is not as high risk of a place as the eastern part of the United States.

Based on the graph on our blog assignment, tornado occurrences appear to have increased over time. This may not be true just because the occurrences have increased because of global warming or other weather phenomena that could increase dramatically one year, but decrease dramatically the next.


The three main requirements for hurricanes to form are 1)consistent heating of the surface, 2)high humidities, and 3)cumulus and cumulonimbus clouds. The ingredients for hurricane formations are warm ocean temps (equator ward 20 N,S), Coriolis needed to initiate the spinning (between >5N, S) and low values of vertical wind sheer. In Japan, because of the location they are called typhoons. Japan is in the red zone for large typhoons and tropical storms, and satisfies all of these requirements for severe weather such as typhoons and tropical depressions/storms.

The different types of formation regions are used because hurricanes are called by different names depending on where they are on the globe. Hurricanes happen in the Atlantic and East Pacific oceans (mainly USA), while cyclones happen in the Indian Ocean near Australia and are normally south of the equator. Typhoons (what Japan has) happen off the coast of China and Indonesia.

http://www.learnnc.org/lp/editions/nchist-recent/6248

As shown above, hurricanes move through the USA from east to west. This is the dominant direction in which hurricanes travel because of the wind sheer and pressure, because the trade winds and winds aloft go in the opposite direction.

Hurricanes (typhoons) happen in Japan, and Okinawa, Japan is right in the pathway for normal "typhoon alley." On average, 10.3 typhoons a year will approach within 300km of Japan. Years in which 12 or more actually strike Japan is considered 'many typhoons' while a year with 8 or less is considered 'few typhoons.' 


Comparing this to the USA, I found 5 hurricanes strike the United States coastline every 3 years. Only two of these hurricanes are expected to be major hurricanes, passing category 3 or higher.