c. TC rainfall in relation to TC intensity
Another factor that may also affect TC rainfall is the TC
intensity. Previous studies suggest that the instantaneous
TC rainfall increases with storm intensity and that the
inner-core mean rain rate of major hurricanes is about 2–3
times larger than that of a tropical storm (Rodgers et al.
1994; Rodgers and Pierce 1995; Jiang et al. 2008). As such,
we also look into the relationship between TC rainfall
severity and TC intensity. As illustrated in Fig. 5, heavier
TC rainfall in Hong Kong is associated with TCs of higher
intensity. The mean maximum sustained wind speed associated
with extreme and moderate TC rainfall is 56
and 53 kt (1 kt 5 0.5144 m s21
), respectively, which are
significantly greater than that of the weak rainfall group
(47 kt) at 99% confidence based on the Student’s t test.
The positive relationship between TC rainfall and TC
intensity is basically in accord with previous studies
(Rodgers and Pierce 1995; Jiang et al. 2008). Besides,
Rodgers and Pierce (1995) previously noticed that the
correlation between the mean rain rate and the maximum
wind speed increases most significantly as TCs intensify
from the stage of depression to tropical storm, while the
correlation becomes weaker for more intense TCs. Similar
to their results, the smaller difference in TC intensity
associated with the extreme and moderate rainfall groups
suggests that other factors, such as TC tracks and moisture
circulations, might play a dominant role in modulating
TC rainfall when TCs become more intense.