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	FAQ FAQs-Meteorological Service General What was the coldest temperature recorded in Singapore? What is Singapore's climate like? What are Sumatras? What are the various sources of meteorological data? How do we forecast the weather? What are the uses of climate data? What is the reference level of the tide measurement? Waterspout How are waterspouts formed? What is the speed and lifespan of a waterspout? How often do waterspouts occur near Singapore waters? Which time of the year do waterspouts occur more frequently? Can waterspouts be forecasted? Are waterspouts dangerous? What are some of the safety tips for waterspouts? Tsunami What is a tsunami? How fast can a tsunami travel and how soon could it impact on coastal areas after it has formed? How can we differentiate a tsunami wave from normal ocean waves? What time of the day are occurrences of tsunamis more likely? How are tsunamis detected? Could Singapore be affected by a tsunami? What should I do if I got caught in a tsunami event? What are the warning signs of tsunami? Any roaring noise, strong wind? Where can additional information on tsunamis be found? Back to Top What is the coldest temperature recorded in Singapore? The lowest minimum temperature ever recorded in the month of December is 20.6 deg C ( on 2 Dec 1964), while the lowest temperature ever recorded (since record began in 1929) is 19.4 deg C (on 31 Jan 1934). Cool weather over Singapore are caused by the following conditions : i ) periods of cloudy to overcast weather accompanied by rain which blocks out the heat from the sun ii ) season and prevailing wind Usually the Northeast Monsoon months of December and January are the cooler months of the year with average highest temperature of 29..9 deg C as compared to 31.5 deg C in the months of April and May, and with average minimum temperature of 23.1 deg C in Dec and Jan as compared to 24.3 deg C in the months of April and May. The early part of the Northeast monsoon (months of December and January) is usually characterised by generally cloudy and windy conditions with rain periods lasting for 2 to 3 days at a stretch. The cool north-east winds which blow over Singapore during this time of the year originate from the cold winter conditions of the interior of the Asian continent. . Back to Top What is Singapore's climate like? Singapore's average annual rainfall is 2357.8 mm. Climatologically speaking, February falls in the latter half of the Northeast Monsoon Season and is a relatively dry month. In fact, it has only 11 raindays as compared to 20 days in December, which lies in the wet part of the Northeast Monsoon. Hence, the drier weather in February is expected. March is the last of the Northeast Monsoon months. There is a tendency for the rainfall to slightly increase in March. This results from a gradual increase in shower activity arising from connective heating in the afternoon and early evening over the island. However, despite the above observations based on long-term records, from year to year there could be variations in the degree of dryness due to annual climatic fluctuations. In general, dry weather is the result of lack of convection or stable atmosphere which prevents the devleopment of rain-bearing clouds. Vertical uplifting of the air is weak when the atmosphere is stable or this could be cause by descending air over a large area ? as is often observed during periods of widespread haze in SW Monsoon months. Winds blowing from dry regions are usually lacking insufficient moisture thus preventing clouds from forming. Strong winds aloft sometimes inhibit the vertical development of rain-bearing clouds. Singapore has two main seasons, the Northeast Monsoon (December to March) and the Southwest Monsoon season (May to September), separated by two relatively shorter inter-monsoon periods. Although there are no distinct wet or dry periods, the mean monthly rainfall shows drier weather conditions from May to July and wetter conditions in the months from November to January. . February is also a relatively dry month. The beginning and end of the monsoons are usually not very well-defined. Hence, from year to year, there could be slight delay in the beginning or end of a monsoon period. This probably accounts for the monthly rainfall anomaly experienced from year to year. Back to Top What are Sumatras? Sumatras are lines of thunderstorms which usually occur between March and November each year. These squalls (lines of thunderstorms) develop at night over Sumatra or the Malacca Straits and move east towards Singapore and Peninsular Malaysia usually during the pre-dawn and early morning. They are often characterised by sudden onset of strong gusty surface winds and heavy rain lasting from 1 to 2 hours as they move across the island. Maximum gusts of up to 50 knots have been recorded during the passage of a Sumatra squall (Gusts are temporary rise in wind speed). Back to Top What are the various sources of meteorological data? Meteorological data are obtained from various sources such as through a network of weather observational stations located at various parts on the island. These observational stations include synoptic stations, weather radars, weather satellites, upper air observing stations and lightning sensors to name a few. Other sources include an exchanged of meteorological data with other national meteorological centres in the region through the Global Telecommunication System (GTS) of the World Meteorological Organisation(WMO). The Singapore National Meteorological Center is linked to counterparts in the neighbouring countries by medium to high-speed telecommunication circuits which form part of the Regional Telecommunications Network of the GTS. Back to Top How do we forecast the weather? Many factors are taken into consideration when a forecast is to be made. One requirement for any forecast is the availability of meteorological data which must be reliable, accurate and regular. With the numerous meteorological data we analyse weather patterns. With the analysed weather charts together with numerical weather prediction products, satellite images, knowledge of the climatology of the area and experience, a forecast is made. Numerical weather prediction products are computer generated forecast models. These run on supercomputers and they provide predictions of on atmospheric vairables such as rainfall, pressure, temperature, wind etc.. Back to Top What are climate data used for? Climate data are used in various industries such as the construction industry, in legal firms, marine industry and many more. Some uses of climate data are given in our Climatological Services webpage Back to Top What is the reference level of the tide measurement? Tides are measured relative to a reference point known as 'Chart Datum'. Chart Datum is the lowest water level recorded over a fixed period (usually 18 years) at a particular point. Back to Top How are waterspouts formed? A waterspout is a weather phenomenon usually observed under cumuliform clouds during intense weather conditions associated with thunderstorms. Due to the lower pressure conditions under the clouds in such conditions, one or two columns of water can be sucked towards the base of the clouds, giving the traditional picture of a funnel. The funnel is really a thin cloud of tiny water droplets. Back to Top What is the speed and lifespan of a waterspout? In waters off Singapore, the speed of the movement of the waterspouts over water could be up to 15 knots. Waterspouts have short life cycle of up to tens of minutes. Back to Top How often do waterspouts occur near Singapore waters? The Meteorological Services does not have any statistics on the occurrences of waterspouts over Singapore waters, as they could not be physically identified on the weather radar. However, an average of one to three occurrences of waterspouts over Singapore waters has been reported yearly. Back to Top Which time of the year do waterspouts occur more frequently Waterspouts can occur at any time of the year, but more likely between March and October when intense thunderstorm formation is highly possible. Back to Top Can waterspouts be forecasted? Waterspouts are generally associated with the occurrence of intense thunderstorms over the sea. However, it is difficult to forecast the occurrence of waterspouts because not all thunderstorms lead to the formation of waterspouts. Back to Top Are waterspouts dangerous Waterspouts are known to dissipate rapidly near the coast and are not expected to cause danger to lives and property on land, besides the usual dangers associated with thunderstorms. Back to Top What are some of the safety tips for waterspouts? If a waterspout is sighted, immediately head at a 90 degree angle from the apparent motion of the waterspout. Never try to navigate through a waterspout. Although waterspouts are usually weaker than tornadoes, they can still produce significant damage to you and your boat. Back to Top What is a tsunami? A tsunami is a series of enormous waves formed in the sea or near the coast and is generated by violent undersea disturbances such as earthquake- induced movement of the ocean floor, landslides and underwater volcanic eruptions. Most tsunamis are caused by earthquakes in the sea that induce movements in the sea floor. From the area where the tsunami originates, waves travel outwards in all directions and can travel great distances. In deep water the tsunami wave is not noticeable, but when it approaches the shore it increases in height. All tsunami are potentially dangerous and can be extremely violent and damaging when they hit the shore. Graphic from 'Tsunami - The Great Waves' (Publication by NOAA/IOC/ITIC/LDG), 2002 Not all earthquakes, however, will produce tsunamis. Normally, it would require an earthquake with a magnitude exceeding 7.5 on the Richter scale to produce a destructive tsunami. Back to Top How fast can a tsunami travel and how soon could it impact on coastal areas after it has formed? In deep ocean, tsunami waves can travel at speed exceeding 800 kilometers per hour and a wave height of less than a meter. As they reach the shallow waters of the coast, the waves slow down and the water can pile up into a wall of destruction tens of meters or more in height. The effects can be amplified where a bay, harbour or lagoon funnels the wave as it moves inland. Large tsunamis have been known to rise over 30 meters. Even a tsunami 3-6 meters high can be very destructive and cause many deaths and injuries Tsunamis can reach coastlines more than 1000 km away within in a few hours Graphic from 'Tsunami - The Great Waves' produced by NOAA/IOC/ITIC and LDG, 2002 Back to Top How can we differentiate a tsunami wave from normal ocean waves? Tsunami waves are distinguish from ocean waves by their great length between wave crests, often exceeding 100 kilometers or more in the deep ocean and by the time between these crests, ranging from 10 minutes to an hour. Often the first wave may not be the largest. The danger from a tsunami can last for several hours after the arrival of the first wave. Back to Top What time of the day are occurrences of tsunamis more likely? Tsunami can occur at any time, day or night. Back to Top How are tsunamis detected? Earthquake monitors and sea level gauges that detect earthquakes and abnormal changes in sea level could be used to detect and provide early warning of tsunamis. Currently the Pacific Tsunami Warning System operates from Hawaii to issue warnings for potential tsunamis in the Pacific Ocean. If a tsunami is detected, coastal areas lying in the predicted path are warned. There is currently no similar system for detection and warning of potential tsunamis in the Indian Ocean. Graphic from 'Tsunami - The Great Waves' produced by NOAA/IOC/ITIC and LDG in 2002 Back to Top Could Singapore be affected by a tsunami? Earthquakes in our region are more prone to occur along the major fault-lines off the outer coasts of Sumatra, Java and the Philippines. Due to its geographic location, Singapore is sheltered by the Indonesian Archipelago in the west and south and the Philippines in the east. Therefore it is very unlikely for Singapore to be directly affected by a tsunami. Back to Top What should I do if I got caught in a tsunami event? If you are at the beach or near the ocean and you feel the earth shake, move immediately to a higher ground. Do not wait for a tsunami warning to be given. In some cases the sudden draw down of sea level resulting in receding of the shoreline, sometimes by a kilometer or more is a sign of preceding or in between crests of tsunami waves. Head for the high ground as quickly as possible. Do not stay at or approach the beach to investigate. If you are advised to evacuate, do so immediately. Stay away from the area until local authorities say it is safe. Do not be fooled into thinking the danger is over after a single wave - a tsunami is not a single wave but a series of waves that can vary in size. Do not go to the shoreline to watch for a tsunami. When you can see the wave, it is often too late to escape. Back to Top What are the warning signs of tsunami? Any roaring noise, strong wind? Tsunamis are caused by an underwater disturbance -- usually an undersea earthquake. Hence, if you feel the ground shaking near the coast, be ready to evacuate at once to higher ground. People who are near the seashore during a strong earthquake are at the highest risk. Rapid changes in the water level are an indication of an approaching tsunami. If you see an unusual disturbance of the ocean, such as the water withdrawing far from shore, it is important to move to high ground. As the waves approach the shallow coastal waters, they may appear normal and the speed decreases. In some cases, the water level may remain low for quite some time, due to the longer period of tsunami waves. However, as the tsunami nears the coastline, it may grow to great height and smash into the shore, causing much destruction. The first wave of a tsunami is generally not the largest. It is important to stay away from the coast until wave activity has subsided, which is commonly several hours or up to days until local authority declares that it is safe. Most important of all, heed all the natural warning signs, as well as the official warnings and advisories issued by local authority. Hence, it may be fairly quiet before a tsunami strikes. When a tsunami approaches, there will be a roaring sound. But the sound of a tsunami will be different from the usual sea surf. There will be a significant departure from the usual higher frequency of sea waves breaking on shore. Tsunamis may or may not be accompanied by strong winds. As mentioned, tsunamis are commonly triggered by undersea earthquakes. They are not meteorological phenomenon, and thus are not usually associated with strong winds or heavy rain. High waves driven by typhoons and storms are called storm surges and are of a different nature from tsunamis. Back to Top Where can additional information on tsunamis be found? Pacific Tsunami Warning Centre http://www.prh.noaa.gov/ptwc/abouttsunamis.htm National Oceanic and Atmospheric Adminstration http://www.noaa.gov/tsunamis.html Back to Top