The Impact of the Typhoon to Peninsular

Malaysia on Orographic Effects

Fuyi Tan, Hwee San Lim and Khiruddin Abdullah School of Physics

Universiti Sains Malaysia

11800, Penang, Malaysia

fuyitan@yahoo.com, hslim@usm.my, khirudd@usm.my

Abstract—Remote sensing techniques have been

used to study the impacts of the tropical cyclone.

In order to figure out the relationship of typhoon

with orography effect, precipitation products are

acquired from Feng Yun 2D; and Global Digital

Elevation Model (GDEM) from ASTER satellite

was applied as well. After combining both the

precipitation and elevation products of

Peninsular Malaysia (PM), rainfall distribution

patterns are distinctly affected by the mountains

range. Titiwangsa Mountain range is the major

mountain range which is able to influence the

movement and distribution of the raining clouds.

Normally, Titiwangsa Mountains can separate

the raining distribution into 2 parts which is east

and west side of the PM. Sometimes, rains can

happen at both sides simultaneously when

allowable weather conditions exist such as during

typhoon activity. The other mountains which are

higher than two thousands meters in PM are also

able to change the rainfall distribution patterns

since some raining clouds are lower than this

elevation. 2 types of typhoon tail effects are

defined by high low pressure system and

centrifugal force reaction.

Keywords-Peninsular Malaysia (PM); rainfall;

mountains; typhoon; pressure

I. INTRODUCTION

The PM is close proximity to one of the

world’s most active cyclogenesis region which

including Western North Pacific (WNP) and

South China Sea (SCS) in the Western Pacific.

This region has 27 cyclones per year in

average with half of them reaching typhoon

intensity. Even though PM is not directly on

the path of these cyclones, certain impacts

have existed during the typhoon season. In

order to study the rainfall distribution patterns

during typhoon season, terrains of PM are

studied as well.

In general, East and West Coast region of

PM have different rainfall patterns in term of

spacial and temporal since these regions are

divided by the Titiwangsa Mountains which is

high enough to affect low level atmospheric

weather condition. Sudden change of the

weather system in synoptic scale such as

tropical cyclone that is significant will

modifies the basic atmospheric state through

the entire troposphere. Thus, regional rainfall

rate and distribution patterns are vary with the

tropical cyclone system.

Typhoon activity almost never bring direct

treat to PM because it is located at equator

region where it is always immune from this

natural disaster. Nevertheless, the tails of the

typhoon has cause the sudden change of the

rainfall rate at that period. In order to study the

indirect impacts of the typhoon to PM; and the

relationship of the typhoon on the topography

in PM, review for the Taiwan studies are made

since Taiwan experiences many typhoons

every year. Therefore, they are extensively

studied for topography or orographic effects to

the tropical cyclone cases. They proved that

close relationship between mountain terrains

and tropical cyclone activities are exist in term

of pressure, wind, track path, intensity and

precipitation.

Previous studied have shown that

significant intensity, structure and track

changes when the typhoon is close to the

island or continental region [1-6]. The terrains-

typhoon interaction caused the track of

typhoon to deflect and sometimes become

discontinuities; at the same time the magnitude

of the wind also reduced by the mountain

range due to friction effect and restriction of

the wind movement; and landfall location may

also affected by the complexity of mountain

ranges. The above studies and experiment also

prove that the orographic effect has to be

considered if the tropical cyclone is

approaching to the continental region because

the complexity of the orographic effect may

influence the activity of the cyclone.

Recently, scientists in different country

have studied the rainfall accumulation and

rainfall distribution patterns of the tropical

cyclone when associate with orographic effect.

The high ranges mountains not only cause the

track to deflect from its origin path but will

also change the typhoon intensity, structure as

2011 IEEE Symposium on Business, Engineering and Industrial Applications (ISBEIA), Langkawi, Malaysia

978-1-4577-1549-5/11/$26.00 ©2011 IEEE 286

well as the rainfall patterns[7]. Even though

Colón-Pagán (2009) has studied the orographic

effects on rainfall induced by the passage of

tropical cyclones over mountainous islands

(focus on the landfall case but not the tail

effect of the typhoon), he found that the

rainfall is maximum in the higher mountain

regions [8].

Besides that, the mountains play an

important role in bringing heavy rainfall by

blocking and convecting warm moist air to the

top of the mountains [9]. In worst case, the

orographic effect will cause flood over the

region in the low plain area due to longer

period of rainfall. Cheung (2008) also suggest

that the orographic effect is one of the

important factor to vary the amount of rain rate

and distribution of rainfall patterns [10]. The

rainfall distribution patterns of the approaching

tropical cyclone will be modified by the

mountains range to a certain degree. The above

studied were related to the case of landfalling

of the tropical cyclone or very near to the

continental region. However, in this study we

were investigating the tail effect of the

typhoon when associated with the mountains

range.

Even though typhoon never makes

landfall into PM, the tails of the typhoon may

also bring certain impacts (heavy rain, strong

wind or even cause to flooding) to PM.

However, the track of typhoon Ketsana in

2009 was not direct influenced by the

orography of PM because of the great distance

between them, so the track and pressure of the

typhoon will not discuss in this study but only

focused on the tail effect of the typhoon in

term of precipitation. Thus, we are using the

FY-2D satellite data and the ASTER satellite

data to determine the relationship of the

orographic effect with the impact tail effect of

the typhoon in PM in term of elevation and

rainfall distribution pattern respectively.

II. STUDY AREA

PM is divided into East and West Coast

region by a mountain range. This mountain

range is called Banjaran Titiwangsa or

Banjaran Besar by locals since this is the main

mountain range that forms the backbone of the

Peninsula Malaysia. The length of this

mountain range is about 480km starts from

Phuket mountain range in Southern Thailand

and ends in the south near Jelebu, Negeri

Sembilan, Malaysia. The highest peak in

Titiwangsa Mountains is Gunung Korbu

2183m (7162ft), the second highest in

Titiwangsa Mountain is Mount Yong Belar

(2181m) and followed by Mount Gayang

(2173m). However the highest peak in

Peninsular Malaysia is Mount Tahan (2187m)

which located at Tahan Range which have

shown in Table 1. The fifth highest in PM is

located at Kelantan (2171m). In addition, 10th

highest mountain in PM is Mount Benum

which is one of the study locations.

Digital Elevation Model of Southeast Asia

with latitude and longitude are edited whereas

PM with latitude 0-8°N and longitude 99-

105°E are focused in this study (refer to Fig.

1). From this figure, topography of the PM is

seen clearly in different height with different

colours.

TABLE I. ELEVATION AND POSITION OF THE MOUNTAINS IN PENINSUALR MALAYSIA

Mountain State Elevation

(m)

Latitude

(N)

Longitude

(E)

Mount

Tahan

Pahang 2187 4°38΄ 102°14΄

Mount Korbu

Perak 2183 4°41΄ 101°18΄

Mount

Yong

Belar

Perak 2181 4°44΄ 101°20΄

Mount Gayang

Perak 2173 4°46΄ 101°22΄

Mount

Chamah

Penang-

Kelantan

2171 5°8΄ 101°20΄

Mount

Benum

Pahang 2107 3°50΄ 102°06΄

Figure 1. The Digital Elevation Model of Southeast Asia with latitude and longitude are edited whereas Peninsular

Malaysia with latitude 0-8°N and longitude 99-105°E are

focused in this study. Triangle areas are the mountains listed at Table 1.

III. METHODOLOGY

The main study is to figure out the

relationship of the typhoon impacts with the

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orographic effects in PM. Mountains

information can be obtained from website

http://www.peakware.com/peaks.html?choice=

AsE. Moreover, according to the Advanced

Spaceborne Thermal Emission and Reflection

Radiometer (ASTER) data

http://asterweb.jpl.nasa.gov/gdem-wist.asp,

global digital elevation model v001 (ASTER

GDEM) have been downloaded and edited by

PCI Geomatics software to produce an

elevation map.

Typhoon Ketsana is one of the most

popular typhoons in year 2009. Thus, satellite

data at this typhoon periods for cloud and

precipitation variation is obtained from

http://satellite.cma.gov.cn/arssen. These

satellite images are analyzed and correlation is

made for rainfall with the mountains region in

PM.

IV. RESULTS AND DISCUSSION

Atmospheric’s circulation change during

tropical cyclone activity. Tropical cyclone

activity varies the weather in PM if the tropical

cyclone track is near the PM region. Basically

the typhoon tail will bring more rainfall and

stronger wind when the typhoon is more

intense and closer to PM. Elsner (2003) stated

that the straight-moving typhoon is significant

threat to Southeast Asia [11]. Thus, typhoon

Ketsana case is chosen in this study because

this typhoon is in reasonable distance and

intensity with stable track (refer to Fig. 2). Fig.

2 shown the typhoon Ketsana almost has

straight line movement. This typhoon activity

provides much information for low level

atmospheric circulation such as changes of

cloud structure, wind variation and

precipitation distribution patterns. This is

because typhoon activity has a strong influence

on the entire tropospheric circulation and

weather of the surrounding regions. Therefore,

one of the impacts of the typhoon Ketsana in

PM region was being studied by using

geostationary satellite and the results is in Fig.

3.

Although the typhoon is not in direct path

to PM but the tail effect of the typhoon is

significant. The intensity of the rainfall can be

referred to the rainfall scale on the images in

Fig. 3. Rainfall patterns are influenced by

typhoon Ketsana since the atmospheric

circulation is changed based on the typhoon

motion. The rainfall distribution pattern at the

northeast PM (refer from Fig. 3a to 3e) was

tend to move toward the center of the typhoon

since the typhoon system has lower pressure

center. Wind is blowing towards the low

pressure center of the typhoon so the clouds

will follow the wind path as well. Thus, the

rainfall distribution patterns tend to distribute

along the outer flow of the typhoon.

Figure 2. The track and stage development of Typhoon Ketsana. *(JWTC)

According to the images Fig. 3a to 3e, the

rainfall patterns are significantly extended

toward typhoon within these 5 hours. Hence,

rotation of the typhoon is believed able to vary

low level atmospheric circulation since the

phenomena proved that typhoon is able to vary

the atmospheric circulation in synoptic scale.

The deeper the central pressure of the typhoon,

the higher the wind speed will move towards

its center. Besides that, typhoon rotation forced

rainfall towards its direction. There is another

factor that is mountains terrain may also

change the rainfall distribution patterns. Many

previous studies have been made for the

typhoon-orography interaction over Taiwan

Island which always hit by the typhoon.

Fig. 3a shows rainfall dominant at the

northeast part of the PM. The rainfall

distribution is blocked by 2nd

to 5th

highest

mountains Mount Korbu; Mount Yong Belar;

Mount Gayang and Mount Chamah

respectively located at the northern part of

Titiwangsa Mountains (refer to Table 1) so no

rain occurs at northwest region but it gather at

northeast regions. Moreover, raining

movement is significantly blocked and slowed

down by the Mount Tahan. Thus no rain

occurs behind this mount. Nevertheless, parts

of the rainfall continue to move forward due to

the typhoon development system. Therefore,

the rainfall pattern is tending to move at east

and northeast direction. This is because the

rainfall location is located at the western south

of the outer flow of the typhoon.

After an hour, the extended rainfall

patterns toward typhoon Ketsana is more

significant (Fig. 3b). Precipitation still unable

to travel through northwest since Titiwangsa

Mountains is high enough to block its

movement. On the other hand, rainfall has

passed over the Mount Tahan because the

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typhoon system forces the cloud move towards

it and then passed over the mount. At this

moment, the rainfall distribution is gathering at

the northeast of PM from higher terrains to

coastal regions. In the following hour (Fig. 3c),

raining patterns is not much different with the

previous hour. The only different at 0215UTC

is the precipitation move forward a bit so rain

stopped over northern part of Kelantan region.

The raining cloud is further extending to

typhoon system.

a) FY2D_PRE_001_OTG_20090927_0015

b) FY2D_PRE_001_OTG_20090927_0115

c) FY2D_PRE_001_OTG_20090927_0215

d) FY2D_PRE_001_OTG_20090927_0315

e) FY2D_PRE_001_OTG_20090927_0415

Figure 3. There are 5 selected FY2D satellite images a) to e) in rainfall distribution patterns study at 27 Sep 2009.

These rainfall images have been correlated with GDEM.

The relationship of hourly rainfall variations (unit in millimeter/mm) on the terrain of Peninsular Malaysia is

shown. At the same time, the impacts of the typhoon

Ketsana is distinct at the northern part of the Peninsular Malaysia where it is full of mountains.

289

Rains had cover through the Titiwangsa

Mountains and move towards northwest part of

PM which can be view in Fig. 3d. At the same

time, raining cloud from the northwest side

also travel to the Titiwangsa Mountains and

meet with the opposite raining cloud at the

northeast side. From the image, the rainfall is

distinct occur at 2nd

to 5th

highest mountains

over the Titiwangsa Mountains (refer to Table

1). Another rainfall event move to south of the

PM had been stuck by the Mount Benum at

Pahang state (near to middle of the PM). The

raining activity is slowed down by Mount

Benum. The other rainfall area over the South

China Sea continues to move forward to

typhoon system.

At 0415 UTC on 27 Sep, most raining

event happened at the center and east side of

PM which are Pahang and Terengganu (refer

to Fig. 3e). Nevertheless, rainfall rate around

this region is also increasing. This rainfall

activity seems like stuck in the lower elevation

area surrounded by higher topography or

mountains terrain. The raining cloud over the

South China Sea is distinctly going to join with

the typhoon system due to the high low

pressure system. In addition, the rainfall rate is

increasing and its coverage becomes wider and

wider when the raining cloud is close to the

typhoon system.

This interaction of typhoon impacts with

orographic effects are supported by [12].

Kodama shows orographic effects dominate

the local weather regime such as significant

impacts on wind flow, temporal and spatial

rainfall distribution patterns. By using Froude

number (Fr = U/NH), where U is the

undisturbed up stream wind speed, N is the

Brunt–Väisälä Frequency, and H is the

obstacle height, airflows will move around the

landmass if Fr is about 0.1 to 0.3. When

airflow encounters high terrain, it will be

stagnated and then deflected and accelerated

around the topography. Generally winds are

able to move over the island if average Fr is

more than 1.0. Studies by [13-15] also have

similar results with [12] even though their

focus regions and techniques are different.

Based on studies of [12-15], precipitation

distribution patterns are directly cause by

airflow conditions with the terrains effect

which is able to affect the movement of the

cloud and raining cloud as well. Hence, in

different typhoon cases will have different

stage of impacts due to different intensity and

different track of the typhoon. This implies

that in different typhoon will have different

rainfall distribution patterns and it is more

complicated when orographic effects are

included. Besides that, I believe the existence

of 2 type of typhoon tail effect in term of

precipitation. One of it is the raining clouds are

separated from the typhoon system and

distribute to the outer region of the typhoon

due to the centrifugal force; and another one is

the raining cloud form rapidly at surrounding

typhoon environment and then moving into the

typhoon system due to the attractive force

which cause by the high low pressure system.

Normally, this tail effect of the typhoon will

not bring heavy rain to the PM region (in this

case the rainfall rate is less than 10mm per

hour) since the typhoon track occur at least in

latitude ≥5°N and always travel in between 10-

15°N. So, PM which located below 8°N is

usually less affected by the typhoon.

V. CONCLUSION

Titiwangsa range and other mountains in PM

(especially northern part) will affect the

rainfall distribution patterns during the impacts

of the typhoon. Low level raining clouds will

be blocked by the high mountains in PM

especially Titiwangsa Mountains which can

divide or separate the rainfall distribution in

western and/or eastern part of PM. When

rainfall clouds encounter the high mountains

region, the low cloud will move along with the

mountains shape and or else may travel

through the top and then only pass over the

mountain due to the wind flow which pushed

the clouds up. Rainfall mostly will occur

around the mountains region due to the raining

clouds are stuck by the mountains in PM.

These high terrain regions also receive higher

rainfall rate due to the longer time of the

rainfall event. Hence, we believe that the high

terrain region of the northern PM will receive

more rain rate during the typhoon season (if

only the typhoon nearby or moves in straight-

moving path which has a reasonable distance

between them). However, further study must

be continued since interactions of the typhoon

with complex terrains are ever-changing.

ACKNOWLEDGEMENT

First of all, I would like thank to my supervisor

and co-supervisor Dr. Lim Hwee San and Prof.

Khirrudin in assisting my work. I also very

appreciate to NASA by providing free ASTER

GDEM data. One cannot be forgotten their

contribution is National Satellite

Meteorological Center (NSMC) from China

Meteorological Administration (CMA) who

providing the free satellite data for this study.

Malaysia Meteorological Department (MMD)

also provided the general climate information

of Malaysia. Joint Warning Typhoon Center

(JWTC) also provided typhoon report for

2009.

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