– 7
The spring range varies with the locality within the Straits from 3.7 metres in the vicinity of One Fathom Bank to 1.6 metres in the vicinity of Horsburgh Light. The prevailing flow is influenced by the NW current which has a rate of about knot but can vary considerably. In the north the
3
4
spring rates vary from about 1 1/2 knots in the main fairways to 1 1/2 to 3 knots in more restricted channels. In the vicinity of Singapore the tidal streams can attain rates of 6 knots with associated eddies and overfalls.
These strong tidal streams cause large uniform sandwaves on the seabed. The height of these sandwaves, which form at right angles to the water flow, varies from 4 to 7 metres. There are also large long sand ridges running parallel with the tidal streams.
The climate of Malacca and Singapore Straits is typically equatorial with uniform high temperature, high humidity and copious rainfall. There are no large air and sea surface temperature variations throughout the year. There are also no distinct wet or dry months as rain falls during every month of the
year.
Two main seasons can be distinguished, namely the Northeast Monsoon and the Southwest Monsoon seasons, with two shorter inter-monsoon periods. The beginning and end of each monsoon is usually not well defined. Generally the Northeast Monsoon is from late November to March and the Southwest Monsoon
from May to September. Prevailing winds are generally northwest to northeast during the Northeast Monsoon and southeast to southwest during the Southwest Monsoon. Wind speeds are on average below 10 knots throughout the year. Occasional strong wind gusts are possible when showers or thunderstorms are in the vicinity.
The most significant weather phenomenon during the Southwest Monsoon and the two inter-monsoon periods is the occasional occurrence of late night and early morning thunderstorm squalls known as "Sumatras". These storms usually give rise to southwest and northwest winds gusting to 20-30 knots and heavy rain. A strong "Sumatra" may produce gusts of 40-50 knots or higher. However, although the onset of these "Sumatras" is sudden, adverse weather conditions associated with them seldom persist for more than one or two hours although moderate to light rain may continue to fall for several hours.
The sea is almost invariably smooth or slight within the Strait with a range of average values from 1/2 to 1 1/2 metres within a period of
3 to 5 seconds
Visibility in general is good over the whole area (10 kilometres or more about 95% frequency and less than 1 kilometre below 0.5% frequency) except during heavy rain squalls. Haze can occur in the southern part of the Strait during the SE monsoon. During 1992 there was a prolonged period of thick haze reducing visibility to less than one kilometre, thought to have been caused by peat on Sumatra smouldering in the heat.
Reliable statistics for the volume of traffic passing through the Straits could not be determined with any certainty, however it is known that over 30,000 ships, of which about 30% are tankers, pass through the Straits annually. In 1992, 81,300 vessels of 75 gross tonnes or over arrived in the Port of Singapore. These figures do not take into account local traffic engaged in trade across the Straits and fishing vessels which are numerous and can be encountered in most areas.
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