Occurrence and Course
There are three areas of high atmospheric pressure around Japan: Pacific, Continental, and Okhotsk high pressure areas. The typhoon related high pressure areas are mainly Pacific and Continental areas, and they move seasonally as shown in fig. 1.
The typhoon occurs on the South Pacific. It moves along the out side of the Pacific to the north west and turns to the north, or goes to the out side of the Continental high pressure areas. The course of the typhoon is affected by the location of two high pressure areas. So the course seasonally changes as shown in fig. 2.
Fig. 1 Two High Pressure Areas
Fig.2 Typical Courses of TyphoonsClassification
Typhoons are classified by their size and strength as shown in Table 1 and 2.
Table 1 The size of the typhoon
(Radius: Vw >= 15m(49ft)/sec)
Size Typhoon's radius km(miles) Large 500(310) <= Radius < 800(497) Very Large 800(497) < Radius Table 2 Typhoon's strength
Strength Max. Vw: m/sec(ft/sec) Strong 33(108) <= Vw < 44(144) Very Strong 44(144) <= Vw < 54(177) Fierce 54(177) <= Vw Damage caused by wind
The relation between wind velocity and damage is shown in Table 3.
Table 3 Relationship between wind velocity and damage
Vw: m/sec(ft/sec) Damage 10(33) It's impossible for anyone to put up their umbrellas 15(49) Signboards begin to fly 20(66) Twigs break 25(82) Roof tiles fly and TV antennas fall 30(98) "Amados" (sliding doors) slip out. Some houses fall The wind velocity around the vortex of air
The typhoon in the Northern Hemisphere is a counterclockwise vortex of air shown as in Fig. 3. When the typhoon is at rest, the wind velocity at the same distance points from the center is almost equal, that is, V=Vw. When the typhoon center moves at a velocity of Vc, the wind velocity on the right side of travelling direction is nearly equal to V=Vw+Vc, and on the left side is V=Vw-Vc: the wind on the right side is stronger than the wind on the left side.
Fig.3 Wind Velocity
Typhoon and Wakayama
We are usually afraid of the typhoons that move northwards on Kii-Suido(Kii channel) and the east end of Shikoku island because the wind in Wakayama City becomes stronger than the other course by the phenomenon shown in Fig. 3.
We had such kind of big typhoons called "Muroto Typhoon" and "The second Muroto Typhoon." The courses were almost the same as shown by the red dotted line in Fig. 4.
Fig.4 Muroto Typhoons
The 1st. Muroto: September 14, 1934, dead and missing persons 3,066.
The 2nd. Muroto: September 15, 1961, dead and missing persons 202.
I heard that the victims of the second Muroto Typhoon were decreased by the improvement of the disaster prevention measures.
