3.2. TC recurving position and track
Tropical cyclone tracks are generally determined by nearby
airflow of the North Pacific high, and TCs tend to move along
the edges of the North Pacific high air mass (Liu and Chan,2008). A TC recurving position refers to the path that a TC
takes when it forms at a low latitude in the northwestern Pacific
and first moves towards the northwest; then, it recurves
towards the northeast as it travels further north. In this study,
TCs that moved straight without any clear recurving position
and TCs that moved in an irregular oval pattern were excluded
from the analysis of the TC recurving position data (e.g., 37
summer TCs and 5 fall TCs were excluded).
Fig. 3 illustrates the difference between summer (JuneeAugust)
and fall (SeptembereNovember) TC recurving positions.
The data show that, on average, summer TCs (28.0N,
125.0E) recurve in the northwest more than fall TCs (25.3N,
126.3E), which means that TCs are more likely to migrate
towards the southern Sea of Japan in the fall and there is a
higher chance of TCs reaching the KP during the summertime.
This result can also be seen in the tracks of TCs shown in
Fig. 4. Fig. 4 illustrates the tracks of both summer and fall TCs
that occurred during 1966e2009. The TCs that affected the
KP took place primarily in the east of the Philippines or from
the northwestern Pacific region. These TCs tend to move towards
the northwest in the beginning and then change direction
towards the northeast once they reach the westerlies
region. As shown in Fig. 4, we found that summer TCs tend to
move farther north than fall TCs and that quite a lot of TCsaffect the KP. The tracks of fall TCs were mostly over the
Japanese Archipelago.
In terms of the average intensity of TCs, it was found that
fall TCs (mean of minimum central pressure: 945.76 hPa,
coefficient of variation: 0.418) were slightly stronger than
summer TCs (mean of minimum central pressure: 959.51 hPa,
coefficient of variation: 0.579). However, there was a relatively
wide range of fluctuations in the minimum central
pressures of fall TCs. The mean frequency of TC genesis was
4.34 per year (coefficient of variation: 0.027) in the summer
and 3.09 per year (coefficient of variation: 0.032) in the fall. It
was also found that the frequency of summer TCs tended to
decrease over time, but the frequency of strong TCs with over
64 knots of maximum wind speed increased. This increase in
the frequency of strong TCs could lead to an increased risk of
flood damage caused by heavy rainfall and strong winds
during the summer season. On the other hand, there were no
statistically significant differences in the frequency of fall TCs
over the KP.