在那个pdf文件里，第14页，写得很清楚：

Singapore’s weather is traditionally classified into 4 periods
according to average prevailing wind directions:
a) Northeast Monsoon Season (December to Early March)
b) Inter-monsoon Period (Late March to May)
c) Southwest Monsoon Season (June to September)
d) Inter-monsoon Period (October to November)
The transitions between the monsoon seasons occur
gradually, generally over a period of 2 months. The winds
during these transitions or Inter-monsoon Periods are usually
light and tend to vary in direction daily.

楼主说 南西季风 这个很郁闷。。。southwest的中文就是西南。。。不是南西。。。