Natural Disaster Research Report of the National Research Institute for Earth Science and Disaster Prevention, No. 45 ; February, 2011

Fujiwhara effect; the interaction between T0917 and T0918
Shinya SHIMOKAWA*, Satoshi IIZUKA*, Takahiro KAYAHARA*,
Shinichi SUZUKI*, and Tomokazu MURAKAMI*
Project for “Study on Long-term Prediction of Typhoon Disaster”
Storm, Flood, and Landslide Research Department,
National Research Institute for Earth Science and Disaster Prevention, Japansimokawa bosai.go.jp, iizuka bosai.go.jp, kayahara bosai.go.jp, ssuzuki bosai.go.jp, tmurakami bosai.go.jp

AbstractTyphoon No.17 in 2009 (T0917) caused severe damage to various parts of the Indochinese Peninsula, especially in thePhilippines because it remained stagnant around Luzon for a very long time with complex movement due to interaction
with Typhoon No. 18 in 2009 (T0918). The interaction between two typhoons is called the Fujiwhara effect. We clarified
the process of the interaction between T0917 and T0918 by using satellite images and typhoon tracks. The southward
movement of T0917, which is a typical consequence of the Fujiwhara effect, was observed.
Key words : Typhoon, Fujiwhara effect, Interaction, Southward movement

1. Introduction
Typhoon No.16 in 2009 (T0916) (Asian name: Ketsana,PAGASA*1) name: Ondoy) formed on September 26, 2009. It
landed on Luzon island (the Philippines) and the Indochinese
Peninsula, causing severe damage to the Philippines,Vietnam, Cambodia, and Laos. Eventually, it became atropical depression around the Indochinese Peninsula on
September 30. Almost 80 percent of metropolitan Manila(the Philippines) was left underwater. The total rainfall forthe nine-hour deluge was 410.6 mm, breaking the previous
single-day record of 334.0 mm in July 1967. The minimumpressure was 960 hPa*2), and the maximum wind speed was35 m/s*2).
Subsequently, Typhoon No.17 in 2009 (T0917) (Asian
name: Parma, PAGASA name: Pepeng) formed on September
29, 2009. After repetition of landing on and leaving fromLuzon, it moved on into the South China Sea. After easing
off into a tropical depression, it strengthened again intoa typhoon. It then landed on Nanhai Island (China), and*1) PAGASA is the abbreviation for the Philippine Atmospheric,Geophysical and Astronomical Services Administration.
*2) Minimum pressures and maximum wind speeds are values
reported by the Japan Meteorological Agency. The rainfalls arevalues reported at the actual location. Dates are expressed using
Greenwich Mean Time (GMT).

finally reverted back to a tropical depression around theGulf of Tonkin on October 14. The minimum pressure was
930 hPa*2), and the maximum wind speed was 50 m/s*2).
Both typhoons caused severe damage to various parts of
the Indochinese Peninsula, especially in the Philippines.
There were three reasons for the large amount of damage.
The first was that T0917 was a very strong typhoon. The
second was that the two typhoons, T0916 and T0917, formed
and landed on Luzon in succession. The third was that T0917
remained stagnant around Luzon for a very long time withcomplex movement due to its interaction with T0918 (SeeFig. 1). The third reason is very interesting in terms of its
physical characteristic. This is the so-called Fujiwhara effect,
which was proposed by Dr. Sakuhei Fujiwhara, the thenhead of the Central Meteorological Observatory of Japan(Fujiwhara, 1921).
2. Fujiwhara Effect
The Fujiwhara effect was originally defined as aninteraction between two typhoons (generally, two vortices
with the same rotating direction) that are separated by up toaround 1,000 km. It causes their centers to begin orbiting
cyclonically (generally in the same rotating direction as thevortices themselves) about a point between the two systems.
Recently, however, it is often used more generally to describe* Tennodai 3-1, Tsukuba, Ibaraki, 305-0006, Japan− 23 −Natural Disaster Research Report of the National Research Institute for Earth Science and Disaster Prevention, No. 45 ; February, 2011㻌Fig. 1 Track of T0917 around Luzon (from the presentation by Ms. Olive Luces (Regional Director, Cordillera AdministrativeRegion, Office of the Civil Defense, the Regional Disaster Coordinating Council of the Philippines) in Cordillera,
Phillippines on 29 November, 2009).

the interactions among two or more nearby typhoons. Realtyphoons not only exhibit simple rotation but also undergo
complex movements governed by the distances between them,
their intensity, and the surrounding winds. Their behavior
patterns are classified into five types: complete merger (CM),partial merger (PM), complete straining out (CSO), partial
straining out (PSO), and elastic interaction (EI) (Dritscheland Waugh, 1992, Prieto et al., 2003). The classification
is based on a dynamic view and not a unique one. Anotherexample of a classification can be found in Nyomura (1986).
A series of typhoons can also exhibit multiple behavior types
as they develop (Lander and Holland, 1993: see also the nextsection).
3. The interaction between T0917 and T0918
Satellite images of T0917 and T0918 showed a changeof behavior from EI to PM, followed by PSO, and then
their separation (EI). Specifically, T0917 and T0918 formed
respectively in succession around the Caroline and Marshallislands around September 29, 2009. At that time, T0918 wassituated to the east of T0917. Both typhoons were then moved
westward by easterly winds. Around the time T0917 landed
on Luzon, T0918 was approaching T0917 at high speed, andthe Fujiwhara effect caused T0917 to stagnate around Luzon(EI; from about October 3-4; Fig. 2a). As T0918 approached

Okinawa, T0917 was absorbed and rapidly weakened byT0918 (PM; from about October 5-6; Fig. 2b). The weakened
T0917 was blown south by a combination of the prevailingwind and the northerly winds generated by T0918 (PSO;
around October 7; Fig. 2c; see also Fig. 1 for southward
movement.). Once the southerly movement of T0917 and thenorth-easterly movement of T0918 had established a greater
separation between them, T0917 regained its power andwas moved west by an easterly wind (EI; around October 8;
Fig. 2d). T0918 moved north-eastward and made landfall inJapan, becoming the only typhoon to do so in 2009.
4. Summary and Discussion
Fig. 3 shows the track of T0917 by the Japan MeteorologicalAgency. The track in Fig. 3, as well as the track in Fig. 1
by the Regional Disaster Coordinating Council of thePhilippines, shows the southward movement of T0917
for October 5 through 8. The behaviors of T0917 after
landing again on Luzon from about October 7 through 8 aredifferent for both track data, although the reason is unknown.
The track by the Japan Meteorological Agency shows acounterclockwise movement, but, the track by the Regional
Disaster Coordinating Council of the Philippines showsa clockwise movement. In any case, track data show thesouthward movement of T0917.

− 24 −

Fujiwhara effect; the interaction between T0917 and T0918 − S. SIMOKAWA et al.

㻌Fig. 2 Infra-red satellite images of South-East Asia taken by the Multi-functional Transport Satellite (MTSAT-1R)(IR1: 10.311.3 μm) in 2009. (a) 12:00, 3 Oct., (b) 06:00, 6 Oct., (c) 12:00, 7 Oct., (d) 06:00, 8 Oct. In (c), T0918 is over theJapanese islands. In (d), T0918 is outside the frame of the image. These images were obtained from the Kochi University
meteorology website (http://weather.is.kochi-u.ac.jp/).

Such a southward movement of a typhoon is a typicalconsequence of the Fujiwhara effect because a single typhoon
does not usually move southward. Similar behavior was also
observed in T0015 (Bopha), which formed on September 6,2000, due to interaction with T0014 (Saomai), which formed
just before T0015 (Wu et al., 2003).
5. Summary and Discussion
We clarified the detailed process of the interaction(Fujiwhara effect) between T0917 and T0918 by usingsatellite images and typhoon tracks. The types of interactionchanged from EI to PM, followed by PSO, and then thetwo typhoons separated (EI). In the process, the southward
movement of T0917, which is not observed in usual
typhoons, was observed. With the repetition of landing on
and leaving from Luzon due to this southward movement,

T0917 remained stagnant around Luzon for a very long time,and caused severe damage to various parts of the Indochinese
Peninsula.
Recently, global warming and its effects on natural
disasters have become severe problems. By global warming,
fewer yet stronger typhoons are expected to be generated(IPCC, 2007). However, there is large uncertainty towards
these predicted results. Some recent studies show the opposite
result; for example, a reduction in strong hurricane frequency
under global warming conditions (Knutson, 2008). Therefore,predicting whether the phenomena described in this reportwill increase or not in the future is very difficult. However,from the viewpoint of disaster prevention, evaluating thechanges in disaster with the changes in typhoon activity by
global warming is important (e. g., Shimokawa et al., 2009,Murakami et al., 2011).

− 25 −

Natural Disaster Research Report of the National Research Institute for Earth Science and Disaster Prevention, No. 45 ; February, 2011

㻌Fig. 3 Track of T0917 by Japan Meteorological Agency (http://www.data.jma.go.jp/fcd/yoho/typhoon/route_map/index.html)..

References
1）Dritschel D.G. and D. W. Waugh (1992): Quantificationof inelastic interactions of vortices in two-dimensionalvortex dynamics. Phys. Fluids A., 4, 1737-1744.
2）Fujiwhara, S. (1921): The natural tendency towards
symmetry of motion and its application as a principle inmeteorology. Q. J. Roy. Meteor. Soc., 47, 287-292.
3）IPCC (Intergovernmental Panel on Climate Change)(2007): Climate Change 2007 - The Physical Science
Basis: Contribution of Working Group I to the Fourth
Assessment Report of the IPCC. Cambridge: Cambridge
University Press, 996 pp.
4）Knutson, T.R., J. J. Sirutis, S. T. Garner, G. A. Vecchi
and I. M. Held, (2008): Simulated reduction in Atlantic
hurricane frequency under twenty-first-century warming
conditions, Nature Geoscience, 1, 359-364.
5）Lander, M. and G. J. Holland (1993): On the interactionof tropical-cyclone-scale vortices. I: Observations , Q. J.
Roy. Meteor. Soc., 119, 1347-1361.
6）Murakami, T., J. Yoshino, T. Yasuda, S. Iizuka and S.
Shimokawa (2011) : Atmosphere-Ocean-Wave Coupled

Model Performing 4DDA with a Tropical Cyclone
Bogussing Scheme to Calculate Storm Surges in an Inner
Bay, Asian J. Environment and Disaster Management, 3,(in press).
7）Nyoumura, Y. (1986): A Typhoon Story-from the Record,
Climb Publishing, Tokyo (in Japanese).
8）Preito, R., B. D. Mcnoldy, S. R. Fulton, and W. H.
Schubert (2003): A Classification of Binary Tropical
Cyclone–Like Vortex Interactions, Mon. Wea. Rev., 131,2656-2666.
9）Shimokawa, S., S. Iizuka, T. Kayahara, and S. Suzuki(2009): Studies on Typhoons and their Disasters in
NIED, Report of the National Research Institute for
Earth Science and Disaster Prevention, 75, 33-40 (inJapanese).
10）Wu, Chun-Chieh, Treng-Shi Huang, Wei-Peng Huang,
and Kun-Hsuan Chou (2003): A New Look at the Binary
Interaction: Potential Vorticity Diagnosis of the Unusual
Southward Movement of Tropical Storm Bopha (2000)
and Its Interaction with Supertyphoon Saomai (2000),
Mon. Wea. Rev., 131, 1289-1300.
(Accepted : November 25, 2010)− 26 −