The Environment 1 309
of the central transitional zone vary depending upon the relative influence of Pearl River water and marine currents.
During the winter dry season, the Kuroshio oceanic current brings warm water of high salinity from the Pacific through the Luzon Strait. The freshwater discharge of the Pearl River is much lower than in the summer and salinity is more uniform across Hong Kong. The coastal Taiwan current also brings cold water from the northeast. down the South China coast, affecting inshore waters.
The normal tidal range in Hong Kong waters is between one and two metres, depending on the relative influence of the moon and sun. The tidal pattern is complex due to the relative effects of the diurnal and semi-diurnal components. The basic pattern during flood tides is for oceanic water to flow north into Mirs Bay and west through Lei Yue Mun into Victoria Harbour and through Kap Shui Mun and the Ma Wan Channel. This flow is reversed during the ebb tide. Maximum tidal currents generally range from 0.5 to 1.5 knots, peaking at up to five knots in narrow channels.
Climate
Hong Kong's climate is subtropical, tending towards the temperate for nearly half the year. November and December are generally regarded as the best months of the year with pleasant breezes, plenty of sunshine and comfortable temperatures.
January and February are cloudier, with occasional cold fronts bringing in cold. northerly winds. Temperatures can drop below 10 degrees Celsius in urban areas. Sub-zero temperatures and frost occur on high ground infrequently. March and April can be mild and pleasant but humid. Fog sometimes disrupts air traffic and ferry services because of reduced visibility.
From May to August, it is hot and humid with occasional showers and thunderstorms. Afternoon temperatures often exceed 31 degrees, but at night temperatures generally stay around 26 degrees.
Hong Kong is more likely to be affected by tropical cyclones between June and October. When a tropical cyclone is some 1 000 kilometres southeast of Hong Kong, the weather is usually fine and exceptionally hot. If cyclones get close they can bring high winds and heavy and widespread rain. Landslips and flooding sometimes cause considerably more damage than the winds.
About 80 per cent of the annual rainfall falls between May and September. August is the wettest month while January is the driest. Severe weather phenomena in Hong Kong include tropical cyclones, strong winter and summer monsoon winds, monsoon troughs and thunderstorms with associated squalls. Waterspouts and hailstorms occur infrequently, while snow and tornadoes are rare.
The Year's Weather
It was the third wettest year on record, mostly due to a very active southwest monsoon in the summer bringing in plenty of moisture. The total rainfall of 3 214.5 millimetres was some 45 per cent above the normal 2 214.3 millimetres. June 2005