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seven squalls a month, and slightly less frequently during the southwest monsoon (June–September), with an average of six a month. In comparison, approximately 2.5 squalls per month are observed during the northeast monsoon from
December to March. Sumatra squalls observe a clear diurnal pattern and are much more likely to occur in the predawn hours (12 a.m. to 6 a.m.
125:, killing four and damaging 56 houses and 36 schools. Fallen trees and power outages were also reported. In the evening of 17 September 2024, a Sumatra squall felled several trees across Singapore, damaging vehicles and blocking roads. Loose items were flung around by winds gusting up to 83.2 km/h (51.7 mph), and a glass roof at
211:
The mechanisms behind the formation and propagation of
Sumatra squalls are not well understood, as observations are sparse and there is thus little data to work with. Several hypotheses exist to explain the development of the initial convective cells that later form the Sumatra squall: heating of air
163:
A 2016 paper by Lo and Orton used data on 1,337 Sumatra squalls affecting
Singapore from January 1988 to December 2009 to compile a climatology of Sumatra squalls. They found that Sumatra squalls occur most commonly during the inter-monsoon periods (April–May and October–November) with an average of
255:
below the front-to-rear jet transporting air back to the surface, and a cold pool at the surface just behind the leading edge. The
Sumatra squall then moves eastwards and grows in size and intensity over the Straits of Malacca, driven by the formation of new convective cells at the squall's leading
109:, Malaysia. A particularly severe Sumatra squall that affected Singapore on 12 June 2014 produced a gust of 103.7 km/h (64.4 mph), and resulted in 54 incidents of fallen trees or branches. Another severe Sumatra squall affected Singapore on 10 July 2014, causing flash floods in
100:
Typically, Sumatra squalls affect
Malaysia and Singapore for one to two hours in the night or morning, producing heavy rains along with wind gusts of 40–80 km/h (25–50 mph). The highest recorded wind gust in Singapore—144.4 km/h (89.7 mph) on 25 April 1984, in
154:
to resolve. Individual forecasters subjectively assessing the outputs of various regional- and global-scale models and analysing real-time observations can have moderately accurate results, though the process is slow and laborious.
132:
Along the
Straits of Malacca, one of the world's most important shipping lanes, the gusty winds of Sumatra squalls make the narrow strait difficult to navigate, which could result in maritime accidents. A letter published in the
272:
is too insignificant to generate enough rotation. The squall peaks in intensity near or over
Malaysia and Singapore, and becomes more diffuse and disorganised after exiting land, eventually dissipating over the South China Sea.
84:. Sumatra squalls typically form in the predawn hours and early morning, and last for a few hours. They may occur at any time of the year, but are most common from April to November, coinciding with the
989:
Ly, Duy Khiem; Tan, Cheng Ann; Ma, Qiang (2016). "Characteristics of
Sumatra Squalls and Modelling of the Squall-Generated Waves". In Gourbesville, Philippe; Cunge, Jean A.; Caignaert, Guy (eds.).
139:
in 1923 noted that boats in the
Straits of Malacca were blown ashore by Sumatra squalls. Sumatra squalls are also responsible for significant lightning activity over the strait. The
187:, despite its influence on thunderstorm activity in the tropics, has no effect on the frequency of Sumatra squalls, though it may serve to enhance their intensity. The presence of
801:
Sun, Xiangming; Huang, Xiang-Yu; Gordon, Chris; Mittermaier, Marion; Beckett, Rebecca; Cheong, Wee Kiong; Barker, Dale; North, Rachel; Semple, Allison (1 April 2019).
240:
below an altitude of 4 km (2.5 mi) and easterlies above that, is necessary for the individual cells to organise into and persist as a squall line.
168:) and morning (6 a.m. to 12 p.m. UTC+8); over half the squalls observed made landfall in Singapore between 3 a.m. and 8 a.m. local time.
135:
150:
Accurately predicting the development of
Sumatra squalls is difficult as the relatively small size of Sumatra squalls make them difficult for conventional
88:
and inter-monsoon periods when the prevailing winds have a greater westerly component. The passage of Sumatra squalls can result in fallen trees,
294:
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Beck, Ferdinand; Bárdossy, András; Seidel, Jochen; Müller, Thomas; Fernandez Sanchis, Elvira; Hauser, Andreas (March 2015).
316:
508:
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Yi, Lan; Lim, Hock (2006). "Semi-idealized COAMPS® simulations of Sumatra squall lines: the role of boundary forcing".
345:
105:—was produced by a Sumatra squall. In 1996, a Sumatra squall caused record-high rainfall and damaging flash floods in
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118:
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can serve to increase the frequency of Sumatra squalls by shifting the prevailing winds to the west or southwest.
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243:
After the initial development phase, the Sumatra squall behaves as a typical squall line, with a front-to-rear
32:
A Sumatra squall over Singapore in the evening of 29 July 2022, viewed from the Stadium Riverside Walk in
608:
184:
859:
He, Shaoneng; Goodkin, Nathalie F.; Kurita, Naoyuki; Wang, Xianfeng; Rubin, Charles Martin (16 April 2018).
802:
640:
Chan, Man Yau; Lo, Jeff Chun‐Fung; Orton, Thomas (May 2019). "The structure of tropical Sumatra squalls".
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associated with squalls can pose a risk to nearby aircraft, especially during landing or takeoff, as the
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over the Western Pacific Ocean and Southeast Asia, resulting in a weaker southwest monsoon. Conversely,
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as it intensifies, but does not evolve further to a comma-shape as the turning effect of the
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777:"CNA Explains: What is a Sumatra squall and how did it bring a sudden storm to Singapore?"
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Ilhamsyah, Y; Koesmaryono, Y; Hidayat, R; Murjaya, J; Nurjaya, I W (February 2017).
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803:"A Subjective and Objective Evaluation of Model Forecasts of Sumatra Squall Events"
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92:, and property damage. Shipping along the Straits of Malacca may also be affected.
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609:"ST Explains: What's a Sumatra squall, and how does it affect S'pore's weather?"
583:"Strong winds, heavy rain batter Singapore, uprooting trees and slowing traffic"
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1038:
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861:"Stable Isotopes of Precipitation During Tropical Sumatra Squalls in Singapore"
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Advances in Geosciences: Solid Earth, Ocean Science & Atmospheric Science
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556:"Elak memandu, berada di tempat terbuka ketika cuaca buruk – MetMalaysia"
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121:. On 17 September 2018, a Sumatra squall impacted the Malaysian state of
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926:"Statistical analysis of sub-daily precipitation extremes in Singapore"
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parcels at the surface by the warm waters of the Straits of Malacca,
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970:. Meteorological Service Singapore. 19 January 2021. p. 8
232:. Once these thunderstorms develop, the presence of vertical
21:"Sumatras" redirects here. For the island in Indonesia, see
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edge (and not by the prevailing winds). The squall forms a
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482:"Sumatra squall brings rain and gusty winds to Singapore"
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536:(in Malay). Universiti Putra Malaysia. 19 September 2018
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generated by air flowing down the eastern slopes of the
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events may result in more frequent Sumatra squalls. The
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IOP Conference Series: Earth and Environmental Science
435:"Wind gust in Friday's storm strongest in eight years"
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Quarterly Journal of the Royal Meteorological Society
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from the east coast of Sumatra and the west coast of
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years, such as 1997 and 2015. This is due to reduced
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Quarterly Journal of the Royal Meteorological Society
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322:. National Environment Agency. 2009. pp. 21–22
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376:"The general features of tropical Sumatra Squalls"
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346:"When the equatorial climate is not so equitable"
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688:"Notes on the "sumatras" of the malacca straits"
236:, caused by contrasting westerlies in the lower
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374:Lo, Jeff Chun-Fung; Orton, Thomas (July 2016).
965:"2020 Climate and Weather: The Year in Review"
865:Journal of Geophysical Research: Atmospheres
991:Advances in Hydroinformatics: SIMHYDRO 2014
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507:Chua, Grace; Aw, Cheng Wei (10 July 2014).
207:Internal structure of a typical squall line
68:, producing heavy rain and gusty winds in
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117:. The squall also felled a tree near the
509:"Storm downs trees, causes traffic jams"
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607:Mujibah, Fatimah (18 September 2024).
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293:. Meteorological Service Singapore.
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344:Bevan, Simon (14 September 2020).
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171:Fewer squalls are observed during
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581:Lee, Elaine (18 September 2024).
452:
433:Rashith, Rahimah (1 April 2018).
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297:from the original on 20 July 2021
291:"Weather Systems: Sumatra Squall"
119:Singapore Institute of Management
16:Squall line in Sumatra, Indonesia
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460:"Fenomena Cuaca: Garis Badai"
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113:and along a slip road on the
64:and moves eastwards over the
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44:(plural: Sumatra squalls or
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185:Madden–Julian oscillation
56:—that develops over the
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807:Weather and Forecasting
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716:(subscription required)
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462:(in Malay). MetMalaysia
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317:"Weatherwise Singapore"
1128:Geography of Singapore
704:10.1002/qj.49704920807
534:"Fenomena Garis Badai"
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877:2018JGRD..123.3812H
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562:. 18 September 2018
392:2016Wthr...71..175L
222:Peninsular Malaysia
70:Peninsular Malaysia
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66:Straits of Malacca
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1008:978-981-287-615-7
613:The Straits Times
587:The Straits Times
513:The Straits Times
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230:Barisan Mountains
189:tropical cyclones
115:Kranji Expressway
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896:10220/45120
486:TODAYonline
238:troposphere
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52:—a line of
50:squall line
1112:Categories
277:References
234:wind shear
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177:convection
141:wind shear
60:island of
58:Indonesian
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268:near the
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191:over the
159:Frequency
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82:Indonesia
74:Singapore
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560:The Star
295:Archived
249:updrafts
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46:Sumatras
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902:20 July
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642:Weather
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380:Weather
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326:20 July
301:20 July
270:equator
181:La Niña
173:El Niño
96:Effects
62:Sumatra
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103:Tengah
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224:, or
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