Petilla et al.
Progress in Earth and Planetary Science(2023) 10:32
https://doi.org/10.1186/s40645-023-00563-1

RESEARCH ARTICLE

Progress in Earth andPlanetary Science

Open Access

Changes in intensity and tracks of tropical
cyclones crossing the central and southern
Philippines from 1979 to 2020: an observational
study
Clint Eldrick R. Petilla1,2, Leia Pauline S. Tonga1,2, Lyndon Mark P. Olaguera1,2,3*   and Jun Matsumoto3,4

Abstract
Observational studies on the characteristics of tropical cyclones (TCs) crossing Mindanao and Visayas Islands, in thesouthern and central Philippines, respectively, remain limited. To address this research gap, this study investigatesthe changes in the translational speeds, the direction of motion, and intensities of 8 and 39 landfalling TCs crossing
Mindanao and Visayas Islands, respectively, from 1979 to 2020. The intensities, translational speeds, and direction of
motions of the TCs were characterized by their position before (approaching point; AP), during (landing point; LP),and after (departing point; DP) traversing through Mindanao and Visayas Islands. The results show a significant linear
relationship in the intensity change between AP and DP, indicating a general weakening of TCs as they traverse bothisland groups. About 5 (29) TCs showed a decrease in intensity based on the maximum sustained wind speed (MSW)
after crossing Mindanao (Visayas). The intensity of TCs with at least Typhoon category upon landfall, decreased on
average (percentage) by about 23.33 kts (− 25.4%) and 24.29 kts (− 45.5%) after crossing Mindanao and Visayas,
respectively. The MSW of weaker TCs decreased on average by about 6.67 kts (− 25.0%) and 8.13 kts (− 20.5%) after
traversing Mindanao and Visayas, respectively. Cases with increased (1 TC for Mindanao and 6 TCs for Visayas) and nochange in intensities (2 TCs for Mindanao and 4 TCs for Visayas) after crossing the island were also found. Landfalling
TCs over Mindanao exhibited a characteristic where those deflected rightward (leftward) at AP tend to be deflectedrightward (leftward) at DP, while no pattern was found for the TCs traversing Visayas. Furthermore, TCs moving acrossMindanao and Visayas tend to decelerate as they approach and move away from the island. The findings of thisstudy are essential for disaster mitigation and a greater understanding of the TCs behavior in terms of intensity, translational speed, and deflection.
Keywords Tropical cyclone, Tracks, Topography, Mindanao, Visayas*Correspondence:
Lyndon Mark P. Olaguera
lmolaguera@observatory.ph
Full list of author information is available at the end of the article© The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to theoriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images orother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line
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Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

1 Introduction
Tropical cyclones (TCs) remain one of the most destructive natural phenomena that induce heavy rainfall events,
flooding, and strong wind damages in many tropical andsubtropical coastal regions around the globe, including
the Philippines (Kubota and Chan 2009; Cayanan et al.
2011; Fudeyasu et al. 2014; Cinco et al. 2016; CorporalLodangco and Leslie 2016; Kubota et al. 2017). The Philippines is located along the corridor of TCs over thewestern North Pacific and ranks 2nd in terms of TC landfall, following China (Wu et al. 2004; Kubota and Chan
2009; Fudeyasu et al. 2014). Recent studies showed thatdamage costs associated with TCs in the Philippines havebeen increasing in recent decades (Cinco et al. 2016;
Basconcillo and Moon 2021). In particular, Basconcillo
and Moon (2021) showed that the damage cost associated with TCs during the December to February season,
which is the less active TC season in the Philippines, andin annual terms have increased after 2012. After thisyear, the estimated annual damage cost has been more
frequently exceeding USD 500 million (see their Fig. 1).
Therefore, it is crucial to analyze the characteristics suchas tracks, landfall patterns, changes in the eye wall structure, and multi-scale spatio-temporal variability of TCs
because of their profound socioeconomic impacts andfor improving the country’s disaster mitigation efforts.
As TCs traverse complex terrain after landfall,
the topography affects their characteristics. Recent
observational and numerical studies show that as a
TC interacts with the land surface, its track and associated rainfall may change depending on the initial
behavior of the TC. For example, the slow movementof Typhoon (TY) IN-FA (2021), when it made landfall in Zhejiang, South China, together with the terrain effects under continuous north/northeasterly air
flow resulted in extreme precipitation. Other factors
include topography providing vertical transport ofwater vapor and the development of low-level verticalcirculation along with the terrain effects, resulting in
prolonged intense rainfall (Yang et al. 2022). Idealized
numerical experiments by Huang et al. (2011) on theinfluence of Taiwan’s topography on the track of TY
KROSA (2007) showed that the terrain height of Taiwan played a crucial role in the looping motion of thetyphoon at its landfall, while the topographic shapeand cloud microphysics only played secondary roles,
while for TY ROANU (2016), the Rakhine mountaininfluenced its movement toward Myanmar; without it,
the TC would have moved northwestward with more
rainfall (Maw and Min 2017). In Luzon Island, northern Philippines, numerical experiments showed that
the Sierra Madre Mountain Range might decrease thetranslational speed of TCs, allowing precipitation to

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accumulate over the island (Racoma et al. 2016). Idealized numerical simulations of Tang and Chan (2014)
showed terrain-induced gyres that caused a northward
deflection of TC tracks when they crossed the Philippines and Taiwan. Brand and Blelloch (1973) examinedthe effects of the Philippine landmass on TC tracks
from 1960 to 1970. They showed an evident impactof the Philippines on the speed, movement, and size
parameters of TCs. In addition, they found a reductionin the average maximum sustained wind speed (MSW)of TCs by about 33% and a northward deflection as
they pass through the islands. Moreover, they notedthat the influence of the landmass on TCs is directly
proportional to the area of the terrains. The Philippines has a complex topography with two major islandgroups to the north and south (Luzon and Mindanao
Islands, respectively), and a sea-island mix at its center(Visayas Islands), which should have less influence on
passing TCs than the former two major island groups.
Recently, Wu and Choy (2015) examined 50 TCs(1980–2014) crossing Luzon Island to determine its
effects on their intensities and motion. Their results
showed that TCs weakened as they passed throughthe terrain of Luzon Island and that TCs accelerated(decelerated) as they approached (moved away). Furthermore, they found that TCs deflected to the right(left) before landfall tend to be deflected to the left
(right) after landfall.
Previous studies that examined the TC activity overthe Philippines mainly focused on the seasonal landfalling TCs using either a large domain (i.e., including
the entire Philippines) (Kubota and Chan 2009; Takagi
and Esteban 2016; Lin and Chou 2018) or those TCs
affecting Luzon Island only (Chou et al. 2011; Wu andChoy 2015; Cruz and Narisma 2016; Racoma et al.
2016, 2021; Bagtasa 2019), while limited studies areavailable for Visayas and Mindanao Islands. Althougha small number of TCs influence Mindanao Island, theassociated damage of these disturbances appears to be
exacerbated by the region’s lack of disaster mitigation
measures as demonstrated by the high damage costsof TS WASHI (2011) and TY BOPHA (2012) (henceforth, TC names will be spelled in capital letters with its
corresponding year enclosed in parenthesis). Furthermore, the topographical characteristics of the major
three island groups in the Philippines are different, asshown in Fig. 1. There are three mountain ranges in
Luzon Island, and two broad valley regions are locatedin between these mountain ranges. Mindanao Island
has a more complex topography, with more mountainous regions, and located closer to the equator, where
the Coriolis effect is small. These geographical features
include the Diwata Mountains, North–South MountainPetilla et al. Progress in Earth and Planetary Science(2023) 10:32

Ranges, Davao Oriental Mountains, and KitangladKalatungan Mountains. Visayas, on the other hand, isa sea-island mix. In this study, the main Visayas Islands
consist of the following: Leyte, Samar, Cebu, Negros,
Panay, Mindoro, and Masbate. Therefore, it is expectedthat the three island groups will have different effects
on the TC tracks, intensity changes, and change intranslational speeds.
Based on the above research gaps, the aim of thisstudy is to determine the changes in intensity, translational speed, and direction of movement of TCs passing
through Visayas and Mindanao Island, which has notbeen examined in previous studies. Most TC studies
over the Philippines focused only on the TC season (i.e.,
June to October). However, more TCs affect Visayas
and Mindanao Island during the off-TC season, whichis the main point of discussion of Rodolfo et al. (2018);
hence, all TCs across all months were analyzed in thisstudy. The findings of this study can assist the government in preparing for future extreme events in theregion. Moreover, understanding the specific changes
in the intensity and movement of TCs over certain terrains can help determine vulnerable areas during such
events and improve mitigation efforts.

2 Data and methodology
This study focused only on the landfalling TCs over
Mindanao Island (5–10° N), southern Philippines, andthose that cross the smaller islands in Visayas, central
Philippines (10–15° N), from 1979 to 2020. Mindanao
Island in this study is defined to be the mainland Mindanao, hereinafter referred to as Mindanao, and excludes
the surrounding smaller islands. Landfalling TCs passing
through the Dinagat Islands, northeast of Mindanao, areexcluded in the definition of landfalling TCs over Mindanao. As for the TCs landfalling over the Visayas, only
those TCs crossing the demarcation lines depicted inFig. 1 (solid thick black lines on the eastern (123° E, 15°
N; 127° E, 10° N) and western coast (119° E, 14° N; 122°
E, 8° N) of central Philippines), were used in the analyses.
The TCs must enter and exit the respective demarcationlines to be considered landfalling TCs over Visayas. TCs
that entered and dissipated while inside the demarcation
area without existing are also included in the study.
Three best track positions were defined in this study
following Wu and Choy (2015), which are the approaching point (AP), landing point (LP), and departing point(DP). The AP is the location before the TC makes landfall, while DP is the location after leaving the landmass of
Mindanao Island. For Visayas, we define AP as the point
before a TC makes landfall in any island near the easterndemarcation line depicted in Fig. 1, while DP is the point
when a TC departs the last island to the west of Visayas

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Fig. 1 Topography (m) and the three major island groups (Luzon,
Visayas, and Mindanao) of the Philippines. The major mountain
ranges are boxed. The thick black lines to the east and west of central
Philippines are the demarcation lines used to filter the landfalling TCs
over the Visayas. (SRTM, https://​www.​usgs.​gov/​cente​rs/​eros/​scien​ce/​
usgs-​eros-​archi​ve-​digit​al-​eleva​tion-​shutt​le-​radar-​topog​raphy-​missi​
on-​srtm-1)

or just before exiting the western demarcation line. All
TCs that crossed Visayas have multiple LPs. For simplicity however, as long as the TCs cross Visayas, they will beconsidered to only have one LP.
The data set used to visualize the different topography features of the Philippine Archipelago was from the
Shuttle Radar Topography Mission of the United States
Geological Survey (SRTM, https://​www.​usgs.​gov/​cente​
rs/​eros/​scien​ce/​usgs-​eros-​archi​ve-​digit​al-​eleva​tion-​shutt​
le-​radar-​topog​raphy-​missi​on-​srtm-1).
TCs that have made landfall in Mindanao regardlessof having an LP or no LP, and continued tracking toward
Visayas were excluded in the definition of landfalling TCs
over Visayas, e.g., SARAH (1983), CANESSA (1991),
JANGMI (2014), etc. TCs without data regarding AP and
DP intensities are also excluded from the study.
The intensity, translational speed, and direction of
movement of the TCs were computed based on the
6-hourly best track archive of the World MeteorologicalOrganization from National Centers for Environmental
Information’s (NCDC) International Best Track Archive
for Climate Stewardship (IBTrACS) (NCDC, https://​Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

www.​ncei.​noaa.​gov/​access/​metad​ata/​landi​ng-​page/​bin/​
iso?​id=​gov.​noaa.​ncdc:​C00834). Both translational speed
and direction of movement at a particular best track
position were derived relative to the future 6-hourly position. The study used the Saffir-Simpson scale when examining TC intensity, ranging from Tropical Depression(TD) at < 33 kts, Tropical Storm (TS) from 34 to 63 kts,
and Categories 1 to 5 having > 63 kts or those at Typhoon(TY) category and above based on the World Meteorological Organization standards.
The translational speed of the TC was computed byfinding the difference between the displacement traveledby the TC from the current TC position and its previous
6-h position and dividing the distance by six.
The deflection of the TC was adapted from the methodology of Wu and Choy (2015) wherein the bearing of the
TC was determined by drawing a line from the current TC
position and its previous 6-h position. Then, the change in
deflection in the next 6-h movement direction relative tothe previous 6-h position is defined to be the deflection. Wu
and Choy (2015) also selected a 5° threshold to differentiate
the transient (Δ < 5°) and significant deflections (Δ ≥ 5°).
To test the significance of the differences in the means,
we used the bootstrapping method for hypothesis testing

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as proposed by Efron and Tibshirani (1993). One of theadvantages of this test is that it does not assume normality (nonparametric) between the samples, unlike an ordinary t-test. More specifically, the test is used to check if
there is a significant difference of the TC’s translational
speed or intensity between the 6-h characteristics (e.g.,
AP − 24 vs AP − 18, AP − 18 vs AP − 12, … DP + 6 vs
DP + 12).
The Pearson Product Moment Correlation was also
used to test whether there is a significant correlation
between two distinct groups. In this experiment, the TC
characteristics (intensity and deflection) were separately
tested to check whether a correlation exists when the TC
is at AP versus at DP. The paired bootstrapping method
was used at 10% significance to compare if there are any
significant changes on TC intensity and translational
speed in 6-hourly intervals. For example, the intensity ofa TC is compared to its intensity 6 h before AP and after(i.e., at AP − 6-AP vs AP–LP).

Fig. 2 Tracks of the a 8 TCs that crossed Mindanao and b 39 TCs over Visayas from 1979 to 2020. The crosses (x marks) indicate the genesis(dissipation) location

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

3 Results and discussion
There were 24 TCs that crossed Mindanao from 1979 to2020. The following TCs with recurving or erratic tracks
were excluded in the analysis: (i) formed/dissipated too
close to Mindanao (4 cases) and (ii) incomplete data
upon landfall in Mindanao since WMO does not provide
the windspeed of TCs less than 30 kts. (12 cases). Ultimately, only 8 TCs crossing Mindanao, shown in Fig. 2a,
were used in this study. The intensities of these TC are
the following: five TSs, two Category 2 TYs (C2s), and
one Category 3 TY (C3). Table 1 lists the TCs passing
through Mindanao, which were tabulated by months.
December was a peak month, with 6 TCs. In general,
there were 3 (37.5%) TCs with intensities having at least
Category 1 TY.
For the Visayas, there were 114 TCs that crossed thecentral Philippines from 1979 to 2020. Note that TCs thathave skirted either the Dinagat Islands or northeastern
Mindanao and made landfall in Visayas were includedin this part of the study. The following TCs with recurving or erratic tracks were also excluded in the analysis:(ii) initially made landfall in Mindanao and continued its
track to Visayas (1 case), and (i) recurved northward anddid not cross the west demarcation line (33 cases), and (ii)incomplete data upon landfall in Mindanao since WMO
does not provide the windspeed of TCs at less than 30
kts. (41 cases). Ultimately, only 39 TCs crossing Visayas,
shown in Fig. 2b, were used in this study. The intensities of these TCs are the following: 18 TSs, 11 C1s, six
C2s, three C3s, and one C4s. Table 2 lists the TCs passing through Visayas, which were tabulated by months.
November and December were peak months similar to
those in Mindanao, with 10 and 15 TCs, respectively. In
general, there were 21 (53%) TCs with intensities having
at least Category 1 TY.
Figure 3a and b shows the locations of AP, LP, and DPof the 8 and 39 TCs that crossed Mindanao and Visayas,
respectively. Similar to Wu and Choy (2015), a track may

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have no LP as an intermediate position within Mindanao
or may have more than one LP points (mostly for TCs
traversing Mindanao in a westward direction or thosethat traversed multiple islands in Visayas). Additionally,
the best-track position 6 h before AP and 6 h after DP
was denoted as AP − 6 and DP + 6, respectively, and asimilar notation will be used to other positions, henceforth. Figure 4 shows some examples of TCs having, one
LP, two LPs, and three LPs over Mindanao. Based on
estimation (computation shown in Sect. 3.1) from thenumber of cases with one LPs, 6 TCs, or 75% of the total
analyzed TCs over Mindanao swept the island within 4
to 15 h. On the other hand, TCs pass through Visayas
within 14 to 37 h.
3.1 Characteristics of tracks

Based on Tables 1 and 2, higher TC landfall frequency
occurs during November and December over Mindanao
and Visayas. More TCs form and traverse the central
and southern Philippines in these months following thesouthward migration of the monsoon trough (e.g., Wanget al. 2007).
For TCs landfalling in Mindanao, there were 6 (75%)
TCs with one LP, 1 (12.5%) TCs with 2 LPs, and 1 (12.5%)
TCs with 3 LPs. After the TCs made landfall in Mindanao, about 7 (87.5%) TCs curved northward, mostly
passing through the Visayas, 1 (12.5%) TC traversed
westward and continued toward the Sulu Sea. One TC
exhibited unique track characteristics, TC JANGMI(2014) exited northeastern Mindanao in a northwesterly
track and then curved southward after passing throughVisayas.
Following the estimation method of Wu and Choy(2015), a TC would likely sweep through a distance of
2–4 degrees of longitude over Mindanao, depending on
its actual track. The distance is computed by getting thedifference of the AP and DP. The 95% confidence interval(CI) of the translation speed at AP is between 11.12 andTable 1 List of tropical cyclones that made landfall over Mindanao Island from 1979 to 2020
JAN

FEB

MAR

APR

MAY

JUN

JUL

AUG​

SEP

OCT

NOV

IKE (1984)RI

MAMIE (1982)

DEC
MARGE (1986)
NELL (1993)
WASHI (2011)
BOPHA (2012)RI & RW
JANGMI (2014)
TEMBIN (2017)

Total

0

0

1

0

0

0

TCs are grouped per month, and the year of occurrence is enclosed in parentheses
RI

TC underwent rapid intensification

RW

TC underwent rapid weakening

0

1

0

0

0

6

0

APR

MAY

JUN

2

ROKE (2005)

TC underwent rapid weakening

1

1

2

NANGKA (2009)

NELSON (1982) OWEN (1994) CHANCHU (2006) DOT (1990)

FEB MARTC underwent rapid intensification

RW

RI

Total 1

ROY (1988)

JAN

Table 2 As in Table 1 but for the landfalling TCs over Visayas
AUG​

1

1

VERA (1983) BETTY (1987)RI

JUL

0

RI & RWRI

5MUIFA (2004)

10

HAIYAN (2013)

RI

DURIAN (2004)RI

15

PHANFONE (2019)RI

NOCK-TEN (2016)RI

MELOR (2015)RI

HAGUPIT (2014)RI & RW

WUKONG (2012)

UTOR (2006)RI

FAITH (1998)

AXEL (1994)RI
RI

LOLA (1993)
NEPARTAK (2003)

MANNY (1993)RI

PHYLLIS (1987)RINORRIS (1986)

BEN (1979)RI

KYLE (1993)

MIKE (1989)

RI

RI

NINA (1987)

IDA (1986)
SKIP (1988)RI

MOLAVE (2020)

DEC

HAZEN (1981)RI & RW LEE (1971)

NOV

SON-TINH (2012)

MIRINAE (2009)

ZACK (1995)

RI

GEORGIA (1986)

SEP OCT

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32
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Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

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Fig. 3 Locations of approaching points (AP; red circle), departing points (DP; blue triangle), and landing points (LP; black circle) of the a 8 landfalling
TCs over Mindanao and b 39 landfalling TCs over Visayas

Fig. 4 Examples of cases with a no LP, b one LP, c two LPs, and d three LPs over Mindanao. Red (black) solid circle shows the AP (LP), and the blue
solid triangle indicates the DP of the TCs

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

16.24 kt. Thus, it can be deduced that most TCs would
take about 7 to 14 h. This is also manifested by the factthat there are 6 (75%) cases of TCs having one LP, whichusually follow a northwesterly direction and traverse
along northeastern and northern Mindanao. Note thatTCs having more than one LP are the cases that traverse
through Mindanao in a generally westerly bearing.
For landfalling TCs in Visayas, we treated all the LPs
as one such that their intensity and translational speed
are averaged into one LP. There were 1 TCs that dissipated while traversing through Visayas which is NORRIS (1986). A TC would likely sweep through a distanceof 4–7 degrees of longitude over Visayas, depending on
its actual track. The distance is computed by getting thedifference of the AP and DP. The 95% CI of the translation speed at AP is between 11.09 and 13.79 kts. Hence,
it can be deduced that most TCs would take about 17 to
30 h. After the TC had made landfall in Visayas, 7 (18%)
TCs curved northward, while 31 (79%) TCs continued
to traverse in a westward direction. One TC exhibited
unique track characteristics, MUIFA (2004) looped in asouth-southwesterly direction before making landfall in
the Bicol Region.
We also checked if there were contrasting features if
seasonal instead of the annual analyses were conducted.
Landfalling TCs during June to October (JJASO) andNovember to March (NDJFM) seasons were examined
separately. In terms of frequency, there were about 1 (7)TCs that made landfall during JJASO (NDJFM) for landfalling TCs in Mindanao, while there were about 9 (28)that made landfall during JJASO (NDJFM) in Visayas. The
tracks of TCs during JJASO are all northwestward andcross the northeastern portion of Mindanao, as shown in
Additional file 1: Figure S1, while those during NDJFM
follow a westerly to northwesterly track. For Visayas(Additional file 1: Figure S2), the TCs during the JJASO
recurve northward toward the northern Indochina Peninsula, while TCs during the NDJFM recurve southward
toward the southern Indochina Peninsula. No significant
pattern regarding intensity and frequency of both seasons
was observed for both Visayas and Mindanao. In terms ofcases of rapid intensification and rapid weakening (RI and
RW), only one TC underwent RI during JJASO (i.e., IKE(1984)). For NDJFM, only one TC has undergone RI and
RW (i.e., BOPHA (2012)). For TCs in Visayas, 17 (4) RI
cases were observed, while 2 (1) RW cases were noted for
NDJFM (JJASO). It can be noted no significant differencein the intensities of the intensity drop of TCs between AP
and DP for Mindanao TCs, while there is a significant difference using bootstrap t test (p = 0.01199) of intensity
drop for Visayas TCs, such that TCs during the NDJFM
have a greater intensity drop than JJASO.

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3.2 Changes in intensity

Figure 5a shows the intensity change from AP − 24 to
DP + 12 for the 8 landfalling TCs in Mindanao. The
results show that, on average, TCs tend to intensify
steadily before landfall and weaken sharply at landfall.
More specifically, the average intensity at AP (DP) is
about 63.38 kts (53.13 kts). Then, the TC weakens steadily as it exits Mindanao. A sharp decrease in intensity canalso be seen from AP to LP, which could be partly attributed to the rapid decrease in wind speed due to friction(e.g., Powell et al. 1991; Wu and Choy 2015; Li et al. 2014,2015), changes in the latent heat supply (Bender et al.
1987), and moisture supply over land (Wong and Chan
2006; Li et al. 2014, 2015). The intensity after DP slightly
decreases before leveling off at DP + 12. During thisperiod, the TC may cross the Zamboanga Peninsula orsome islands to the north of Mindanao. However, someTCs may re-intensify after DP + 12, particularly thosecrossing the South China Sea-West Philippine Sea, such
as TC, TEMBIN (2017).
For the 39 TCs landfalling in Visayas, Fig. 5b shows
the intensity change from AP − 24 to DP + 12. Similar tothe patterns observed in Mindanao, TCs tend to intensify steadily before landfall and weaken sharply at landfall. More specifically, the average intensity at AP (DP) is
about 67.95 kts (54.36 kts). A sharp decrease in intensity
can also be seen from AP to LP. The intensity decreases
before leveling off at DP and slightly increases fromDP + 6 to DP + 12 since the TCs may cross the South
China Sea-West Philippine Sea. Additionally TCs may reintensify after DP + 12 such that 4 TCs intensified up to
TD/TS, 6 TCs up to C1, 6 TCs up to C2, 5 TCs up to C3,
and 4 TCs up to C4. For both areas of study, the results
are consistent with the findings of Brand and Blelloch(1973), Bender et al. (1987), and Wu and Choy (2015)
where re-intensification usually starts about 12 h after
landfall.
Figure 6a shows that stronger TCs, in general, tend tohave larger decreases in intensity, while the intensity of
weaker TCs appears to be less affected by Mindanao’s
topography. More specifically, there exists a significant
positive linear relationship for the TC’s intensity drop
before and after landfall (p = 0.0041; significant at 10%;r = 0.88; Fig. 6e). There were 2 (25%) TCs that maintained their intensities, particularly those at TS categories, while 5 (63%) TCs decreased in intensities. About 1(13%) TCs also show a slight strengthening by about 5 kts
after traversing through Mindanao (Fig. 6a, b). For landfalling Visayas TCs, Fig. 6c shows that stronger TCs, ingeneral, tend to have larger decreases in intensity, while
the intensity of weaker TCs appear to be less affected by
Visayas’s topography (Fig. 6c, d). More specifically, there
exists a significant positive linear relationship for thePetilla et al. Progress in Earth and Planetary Science(2023) 10:32

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Fig. 5 Temporal variation of the average maximum sustained wind speed of the TCs from AP − 24 to D + 12 over a Mindanao and b Visayas. Solidline (dashed line) represents the difference between the intensity at two positions is (not) significant at 10% based on bootstrapped t test. Error bars
represent 95% CI

TC’s intensity drop before and after landfall (p < 0.00001;
significant at 10%; r = 0.71; Fig. 6f ). For both Visayas
and Mindanao, the results were consistent with thefindings of Brand and Blelloch (1973), who observed asimilar effect of the Philippines on landfalling TCs. However, TCs passing through Visayas exhibit lesser casesof strengthening such that 6 (15%) TCs increased inintensity, while there were 4 (10%) TCs that maintained

intensity, particularly those with strength at TS category,
while 29 (74%) decreased for TS and TY categories.
Landfalling Visayas TCs are more prone to intensification due to the sea-island mix from the archipelagic
geography (Brand and Blelloch 1973). According to Wu
and Choy (2015) and Powell and Houston (1996), theincreased turbulence induced by larger roughness overland may have more impact on weaker TCs. It is also
important to note that no TCs with at least TY intensities

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

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Fig. 6 a Frequency distribution of the intensity change over Mindanao and b over Visayas. c Scatter diagram showing the intensity change
between AP and DP with respect to different TC categories over Mindanao and d over Visayas. The numbers inside the black circles indicate thetotal number of cases if it is larger than one. The numbers inside the parentheses at the bottom of the figure indicate the total number of cases forthe different TC categories. Relationship of the maximum sustained winds (MSWs) at AP and DP over e Mindanao and f over Visayas.

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

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Fig. 7 Examples of cases with a, b increased intensity, c, d maintained intensity, and e, f decreased intensity based on the MSW difference between
AP and DP, after crossing Mindanao (a, c, e) and Visayas (b, d, f). Points are color coded according to the Saffir–Simpson scale

experienced intensification while passing throughMindanao.
One probable cause that TCs at TS category maintained its strength while traversing is the moisture provided by the sea-island mix. More specifically, Sugino
and Satomura (2010) examined the characteristics of 98
typhoons crossing the Indochina Peninsula from 1979
to 2004, particularly the lifetime after landfall. They

examined two weak typhoon cases (USAGI (2001) andLOLA (1990)) whose lifetimes are longer than normal.
They found that typhoon USAGI (2001) passed through ahumid region over the Indochina Peninsula, while LOLA
(1990) passed near the Gulf of Thailand, which they
hypothesized to have resupplied the moisture for the
maintenance of these two typhoons.

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

For TCs landfalling in Mindanao, the decrease in the
MSW of TCs classified as TS is usually ≤ 15 kts, with anaverage decrease of 6.67 kts, whereas for TCs at TY categories is usually ≥ 15 kts, with an average decrease of
23.33 kts. More specifically, there is a significant difference between the intensities at AP and DP (p = 0.0935;
at 10% significance). Based on Fig. 6b, there are 5 cases(63%) with a decrease in MSW listed as follows: TS (2),greater than C1 or TYs (3). The average drop in intensity for TS is about 25.0% with a 95% CI of 20–30% as
estimated by bootstrapping. For TCs having at least a
TY category, the average drop in intensity is about 25.4%
with the 95% CI of 16.6–30.0% as estimated by bootstrapping. Overall, the drop in intensity for TCs having at least
a TY category is less than 50%. This also coincides withthe study of Kaplan and Demaria (1995), where the windspeed decay rate after landfall is proportional to windspeed. Only 1 TC, MARGE (1986), with a TS category
has been reported to increase in intensity by 5 kts, which
is about a 9.09% increase from its initial strength at AP.
For landfalling TCs in Visayas, the decrease in the
MSW of TCs with intensities at TD and TS is usually ≤ 10
kts, with an average decrease of 8.13 kts, whereas for TCs
at TY categories, it is usually ≥ 20 kts, with an average
decrease of 24.29 kts. More specifically, there is a significant difference in the intensities between AP and DP(p = 0.0225; at 10% significance). Based on Fig. 7, there
are 29 cases (74%) with decrease in MSW listed as follows: TS (8), ≥ C1 TYs (21). The average drop in intensity
for TSs is about 20.5% with a 95% CI of 11.8–22.5% asestimated by bootstrapping. For TCs having at least a
TY category, the average drop in intensity is about 45.5%
with the 95% CI of 26.1–54.6%. Additionally, the intensity
drop is consistent with the study of Kaplan and Demaria (1995) where the wind speed decay rate after landfall is proportional to wind speed. Only 6 TC, all in TS
category, has been reported to increase by an average of
7.5 kts, which is about a 14.1% increase from its initialstrength at AP.
Figure 7 summarizes the tracks of TCs whose intensities increased, maintained, or decreased while traversing Mindanao and Visayas. It can be noted that theTCs traversing Mindanao with increased or maintained
intensities (Fig. 7a, c) are weaker TCs (i.e., TD or TS categories) and traversed through northern and northeastern Mindanao, which is a small portion of land. Chouet al. (2011) also found similar cases of TCs crossing asmall portion of landmass over Luzon Island and Taiwan.
The TCs that have maintained or increased their intensities after traversing Visayas are usually weaker TCs (i.e.,
TD or TS categories) are shown in Fig. 7b, d, except for
CHANCHU (2006), which maintained intensity as a Category 1 TY. It can also be observed that TCs, which have

Page 12 of 23

increased in intensities, followed a northwesterly direction. For both Visayas and Mindanao, stronger TCs hadgreater tendency to decrease in intensity upon departure.
We also examined the TCs that exhibit rapid intensification (RI) and rapid weakening (RW) as they approach
Visayas and Mindanao. DeMaria et al. (2012) defined
RI and RW as a ≥ 30 kt increase and ≥ 20 kt decrease,respectively, within 24 h. Hence, following their definition, we examined cases with RI and RW for landfalling TCs in Visayas and Mindanao. This study used the
TC strength between the genesis point and AP to checkcases with RI/RW. For Mindanao, there were only 2cases of RI, specifically IKE (1984) and BOPHA (2012).
Note that BOPHA (2012) underwent both RI and RW
throughout its lifetime. For Visayas, there were 21 (53%)
cases of RI, shown in Table 2, while there were 3 cases(8%) of RW, which are HAZEN (1981), MIRINAE (2009),
HAGUPIT (2014). If the RI and RW cases were to be
divided between the June, July, August, September, October (JJASO) and November, December, January, February, March (NDJFM) seasons, only one TC underwent
RI for each season of JJASO and NDJFM, while one caseof RW in NDJFM for Mindanao. For Visayas, 17 (4) RI
cases were reported during the NDJFM (JJASO), and 2(1) RW cases in NDJFM (JJASO). Wu and Choy (2015)
noted that RI and RW are caused by numerous dynamic
and thermodynamic processes such as sea surface temperature and vertical wind shear. In summary, RI and
RW cases are rare in the observed TCs that made landfall
over Mindanao (25% and 25%, respectively) compared to
TCs landfalling in Visayas, which have a higher tendency
to undergo RI and RW (53% and 8%, respectively).
3.3 Changes in translational speed

The changes in the translational speed are shown in
Fig. 8. For Mindanao TCs (Fig. 8a), it is evident that thetranslational speed maintains prior to AP while reaching maximum at AP − 18 and decreases abruptly until LP,
while for Visayas TCs (Fig. 8b), the translational speed
steadily increases until it peaks at DP, then decreases at
positions greater than DP. This result is different fromthose found by Wu and Choy (2015) where they foundthe peak at AP, which is 6 h prior to LP due to the interaction of the TC with topography. The gain in speed fromAP − 24 to AP − 6 may be unrelated to the topographyof the island as also noted by Wu and Choy (2015) for
Luzon Island. Both Visayas and Mindanao also show that
there is no relationship between changes in translational
speed and intensity of TCs.
The difference in translational speeds at AP and DP
can be better illustrated from their bootstrapped distribution, as shown in Fig. 9a, b for landfalling TCs over
Mindanao and Visayas, respectively. For Mindanao, thePetilla et al. Progress in Earth and Planetary Science(2023) 10:32

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Fig. 8 As in Fig. 5 but for the average translational speed, (a) for Mindanao and (b) for Visayas

average translational speed at AP and DP is 13.68 kts and14.41 kts, respectively. The corresponding 95% CI for AP
and DP is 11.12 kts to 16.23 kts and 11.96 to 16.86 kts,
respectively. For Visayas, the average speed at AP and DP
is 12.40 kts and 13.11 kts, respectively. The corresponding 95% CI for AP and DP is 11.09 kts to 13.17 kts and11.94 to 14.27 kts, respectively. Based on the significancetest via bootstrapping between AP and DP, there is no
significant difference in the translational speeds of TCs
before and after landfall for both island groups. Bothscenarios require further examination because TCs are
expected to slow down after encountering land surface
due to increased friction and loss of latent heat. It is possible that the TCs crossing Mindanao Island encountereda humid environment (e.g., Sugino and Satomura 2010)or that the soil was wetter than normal conditions, which
may provide adequate energy to sustain TCs in a similarmanner to the ocean environment (Andersen et al. 2013).
Likewise, Brand and Blelloch (1973) noted that central

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

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Fig. 9 Bootstrapped distribution of the translational speed at AP (blue) and DP (white) for a Mindanao and b Visayas. Comparison of thetranslational speeds at AP − 6 and AP for the c 8 TCs over Mindanao and d 39 TCs over Visayas, sorted in ascending order of the speeds at AP − 6.
Increase (decrease) in speeds is shaded in red (blue). One TC over Mindanao, while three TCs over Visayas were excluded since they had no position
at AP − 12, which is necessary for computing the translational speed at AP − 6regions of the Philippines have less effect on the storms
due to Sea-Island mix and small land surface areas.
We further examine the conditions at AP and AP − 6,as shown in Fig. 9c for Mindanao and Fig. 9d for Visayas.
For TCs in Mindanao, about 3 (5) TCs accelerated (decelerated) or 38% (63%), as they approached the island.
However in Visayas, about 19 (20) TCs accelerated(decelerated) or 49% (51%) as they approached the island.
More specifically, the average change in translational
speed from AP − 6 to AP is about − 0.61 kt and 0.028 kt
for Mindanao and Visayas, respectively. Previous studies suggest that the increase in translational speed prior
to landfall may be related to the interaction of TCs withthe topography (Chang 1982; Bender et al. 1987) and friction-induced asymmetry in the large-scale flow, which isone of the reasons for TC drift (Wong and Chan 2006).
Additionally, the change in translational speeds of
TCs after leaving both Mindanao and Visayas (comparing the TS at points DP and DP + 6) was also investigated. For Mindanao, there were 7 or 88% of the cases
showing deceleration and 1 case for acceleration. For
Visayas, 15 (23) or 38% (59%) cases showed acceleration(deceleration), while 1 (3%) TCs maintained their translational speeds. More specifically, the average change intranslational speed from DP to DP + 6 is about − 1.06 kt
and − 1.00 kt for Mindanao and Visayas, respectively.
3.4 Changes in direction of motion

Similar to the methodology of Wu and Choy (2015), in
this study, the change in the 6-h movement direction
relative to the previous 6-h position is defined to be thedeflection. The deflections at AP and DP are examined inthis section such that only cases with one LP for Mindanao were considered, while all TCs regardless of thenumber of LP were analyzed in Visayas for simplicity;
hence, only 6 TCs out of 8 were examined in Mindanao
and all of the 39 cases were examined in Visayas as illustrated in Figs. 10 and 11. To reiterate, a 5-degree threshold similar to those used by Wu and Choy (2015) for the
deflection angle was used to filter out transient wobbles (Δ <|5°|) in the tracks of small amplitudes. Positive

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

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Fig. 10 Comparison of the deflections at AP and DP for those cases with one LP over a Mindanao and b Visayas. For Visayas, all TCs have multiple
LPs, but for simplicity, we only treated them as one LP if they are within the demarcation line depicted in Fig. 1. Positive (negative) values, indicatedby red (blue) bars represent deflections to the right (left). Yellow squares indicate TCs with at least TY intensity(negative) values represent deflections to the right (left),
i.e., clockwise (counterclockwise) deflections. The caseswith deflections Δ ≥ 5° are also summarized in Table 3
which can be noted that the magnitude of deflectionsat AP is generally larger than those at DP (Fig. 10). For
Mindanao and Visayas (Fig. 10a, b), all cases at AP and
DP are within ± 20°.
Figure 11a categorizes the number of TCs that are
deflected at AP and DP based on deflection angles over
Mindanao. In the AP, about 4 TCs were deflected rightward, 3 of which have at least TY category. Additionally,
there were 2 TCs having transient deflection (within ± 5°),
while no TCs were deflected leftward. Based on Table 3,
about 66% of the TCs show deflections at AP, while only

33% show deflections at DP. There is also an apparent tendency for strong TCs (≥ C1) to be deflected to the right at
AP (100%), and none at DP (0%). This indicates an apparent effect of topography on stronger TCs at or near landfall. Weaker TCs appear to be deflected more to the leftof DP (66%) than to the right at AP (33%). TCs that had
made landfall in Mindanao showed that all TCs having a
TY category are deflected to the right at AP and require
further numerical simulations to explain the northward(rightward or positive) deflection of TCs in Mindanao
due to the different terrain features. Wu and Choy (2015)
also noted that the direction change may also be attributed to the uncertainty of position and that further study

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

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Fig. 11 Deflection at AP and DP for the a 6 TC cases with at least one LP point over Mindanao and b 39 TC cases over Visayas. Red (Blue) solid line
indicates positive or rightward (negative or leftward) deflection of 5° or more, whereas the green dashed line represents a deflection less than 5°.
Cases with maximum sustained wind ≥ C1 category are given inside the parenthesis

is required to determine whether there are significant or
abrupt changes at AP and DP due to topography.
Based on Fig. 11b, over Visayas, 12 TCs were deflectedrightward, 6 of which have at least TY category. There
were 20 TCs that underwent transient deflection(within ± 5°), 12 of which have a TY category. Moreover,
7 TCs were deflected leftward, 3 of which having at least
TY category. The results show that there is no significant
pattern for the TC deflection at DP as the number of TC
deflection is distributed across the categories and that

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

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Table 3 Summary of the deflection (Δ) in the 6-h movement direction at AP and DP of landfalling Mindanao TCs using a thresholdof ± 5°. Refer to Figs. 11 and 12 for the counting of cases. Note that Δ ≥ 5° degrees (< − 5°) are regarded as positive or rightward(negative or leftward) deflection
Intensity

Cases

At AP
Δ > 5°At DP
Δ < −5°|Δ| ≥ 5°

Δ > 5°

Δ < −5°|Δ| ≥ 5°MINDANAO
All TCs640

4 (66%)

02

2 (33%)

> TY

3

3

0

3 (100%)000 (0%)

TD/TS

3

1

0

1 (33%)

02

2 (66%)All TCs

39

12

7

19 (49%)163

19 (49%)

> TY

21

6

3

9 (43%)

81

9 (43%)

TD/TS

18

6

4

10 (56%)82

10 (56%)

VISAYAStransient deflections comprise the majority of the count.
Based on Table 3, about 49% of the TCs (19 cases) show
deflections at AP and DP. Note that there exists an apparent tendency for weaker TCs to be either deflected to theleft or right at AP and DP for TCs landfalling in Visayas,
which is contradictory to the observations made in
Mindanao where TCs are deflected to the right at AP andleft at DP. There also exists a strong tendency for a TC to
be deflected to the right at both AP and DP for both > TY
and TS categories.
More specifically in the Visayas region, weaker TCs
appear to be deflected at AP (56%) and DP (56%) thanstronger TCs (43%). This is supported by the findings ofWang et al. (1999) and Wu and Choy (2015), where they
noted that topography is more effective in deflecting
weaker TCs. For Visayas TCs having a strength greaterthan TY category, a deflection to the right is more apparent in both the AP and DP.
Contrary to Wu and Choy’s (2015) findings of anegative correlation for TCs passing through Luzon(r = − 0.65; p value not given) between the deflection
angles at AP and DP, a significant and positive correlation between AP and DP (r = 0.8218; p = 0.0123) was
found in Mindanao and an insignificant and positive
correlation between AP and DP (r = 0.0091; p = 0.9561)
was found in Visayas cases as shown in Fig. 12, wasfound in this study. Note that all of the TC deflection(including the transient wobbles of < 5°) were taken into
account. To demonstrate this positive linear relationship, such that deflection to the left (right) at AP corresponds to the deflection to the left (right) at DP, we
illustrate 3 sample cases for Mindanao in Fig. 13a, b.
Examples of TCs that were deflected leftward both at
AP and DP are WASHI (2011), while examples of TCs
that exhibited rightward deflections both at AP and DP
are IKE (1984), NELL (1993). Additionally there were 5

Fig. 12 Comparison of the deflections at AP and DP for the a 6 caseswith deflections over Mindanao and b 39 cases with deflections over
Visayas. The solid lines represent the linear trends

TCs that exhibited a different change in direction at AP
and DP, which are MARGE (1986), BOPHA (2012), andJANGMI (2014). For TCs which had made landfall in
Visayas, some TCs exhibited similar changes in direction as shown in Fig. 13c, d. However, there is no significant relationship between the deflection angles at
AP and DP as shown earlier in Fig. 12b. This may be

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

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Fig. 13 Examples of cases with leftward (leftward) and rightward (rightward) deflection at AP (DP) over Mindanao (a, b) and Visayas (c, d)attributed to the fact that the inter-island deflections
were ignored in this study.
Wu and Choy (2015) noted that the conditions likely toindicate whether a TC would have a left or right deflection at AP may be determined by cross-examining thetranslational speed, intensity, and direction of motion
from AP − 24 to AP − 6 as shown in Fig. 14a, b for Mindanao and Visayas, respectively. For TCs passing throughMindanao, TCs deflected to the right at AP tend to be
more intense, the translational speed generally consistent,
and the direction of motion varied across all approaching
points. For TCs having a transient deflection, it can beobserved that they are generally weaker compared to theTCs that were deflected positively. It is important to notethat there was only one TC with a transient deflection atAP − 12 to AP − 24 since incomplete data were retrieved
from the JANGMI (2014). As such, this does not provide
a clear and convincing representation of Mindanao TCs
that were deflected to the left. For TCs passing throughVisayas, in the order of greatest to least intensity, TCs
that would undergo transient deflection tend to be themost intense, followed by TCs deflected to the right, thenTCs deflected to the left. In terms of translational speed,in the order of greatest to least magnitude, TCs thatwould be deflected to the right have the greatest speed,
followed by TCs that would undergo transient deflection, then TCs deflected to the left. In terms of the direction of motion, TCs deflected to the right at AP follow anorthwesterly track before landfall, while TCS that would
undergo transient deflection and deflection to the left at
AP follow a more westward direction. In comparison, theresults of Visayas (Mindanao) TCs conform (contradict)with landfalling Luzon TCs from Wu and Choy (2015)
such that TCs undergoing a transient (significant rightward) deflection at AP are the most intense compared tothe other deflection classification.
3.5 Comparison of TC behavior in Luzon, Visayas,
and Mindanao

Table 4 summarizes the differences in the impact of
the Luzon, Visayas, and Mindanao on the intensity,

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

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Fig. 14 Comparison of temporal variation of the average intensity (top) translation speed (middle) and direction of motion (bottom) from AP − 6 toAP − 24 for different groups in terms of the deflections at AP for a Mindanao and b Visayas. The whiskers indicate maximum and minimum values,
the upper and lower limits of the box indicate 75th and 25th percentile, respectively, the solid black line indicates the median, and the circles
outside the whiskers indicate outliers. Red (blue) indicates positive or rightward (negative or leftward) deflection cases. Green indicates otherwise
cases which are transient deflection cases (i.e., deflection |Δ|< 5°)translational speed, and direction of motion of landfalling TCs in each region. The results for Luzon Island
shown in this table were based on Wu and Choy (2015).
In contrast to those landfalling TCs over Luzon, where

there is a logarithmic relationship between DP and
AP, TCs crossing in Mindanao and Visayas have a linear
relationship between DP and AP. This may be attributed to the distance across each islands and island

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

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Table 4 Regional comparison of the changes in intensities, translation speeds, and direction of motions of landfalling TCs over Luzon,
Visayas, and Mindanao. The results for Luzon Island were based on Wu and Choy (2015)
Luzon

VisayasMindanao

Data and methods

Landfalling Luzon TCs at > 15° N arerecorded
50 TCs from 1980 to 2014
More frequent storms during JJASO than
NDJFM

TC passing through the defined demarcation lines between 10 and 15°N
39 TCs from 1979 to 2020
More frequent storms during NDJFM
than JJASO

Landfalling Mindanao TCs
8 TCs from 1979 to 2020
More frequent storms during NDJFM thanJJASOIntensity

Average intensity at AP is 69.2 kts
Decrease in TC intensity at AP versus DP(logarithmic relationship)
Estimated intensity drop for TD and TS
is less than 10 kts, while for TY is greaterthan 10 kts
6 cases with intensity increase for Luzon
TCs (TS & TD Category)
11 RI and 3 RW (24 h before AP and
AP − 6)
Intensity drop levels off at DP + 6

Average intensity at AP is 67.95 kts, while
DP is 54.36 kts
Decrease in TC intensity at AP versus DP(linear relationship)
Average intensity drop for TS is 8.13
kts (− 20.5%), while for TY is 24.29 kts(− 45.5%)
Average intensity increase for TS is about
7.5
6 cases with intensity increase for Visayas
TCs (6 TS)
21 RI and 3 RW (from genesis to AP)
Intensity drop levels off at DP

Average intensity at AP is 63.38 kts, while
DP is 53.13 kts
Decrease in TC Intensity at AP versus DP(linear relationship)
Average intensity drop for TS is 6.67
kts (− 25.0%), while for TY is 23.33 kts(− 25.4%)
Average intensity increase for TS is 5 kts
2 cases with intensity increase for Mindanao TCs (TS)
2 RI and 1 RW (from genesis to AP)
Intensity drop levels off at DP + 6

Translational Speed Average TS at AP is 12.8–14.8 kts (95% CI)
TC takes about 6 to 9 h to transverseLuzon
TC accelerates (decelerates) as it
approaches (departs) from Luzon Island

Average TS at AP is 11.09–13.79 kts (95%CI)
TC takes about 17 to 30 h to traverse
VisayasTC decelerates as it approaches anddeparts Visayas

Average TS at AP is 11.12–16.24 kts (95%CI)
TC takes about 7 to 14 h to traverse
Mindanao
TC decelerates as it approaches anddeparts Mindanao

Direction of Motion Weaker TCs have a greater tendency to
be deflected at AP compared to stronger
TCs
Stronger TCs have a greater tendency to
be deflected at DP than AP
Negative correlation at DP versus AP
direction change (opposite deflection)
Higher TC deflection tendency at DP thanat AP

Weaker TCs have a greater tendency to
be deflected both at AP and DP compared to stronger TCs
No correlation at DP versus AP directionchangeSimilar TC deflection tendency at AP andaYangt DP

Stronger TCs have a greater tendency to
be deflected at AP than DP
All TCs at TY are deflected to the right atAP
Two TCs deflected to the left at DP
Positive correlation at DP versus AP direction change (same direction deflection)
Higher TC deflection tendency at AP thanat DPgroup (i.e., Luzon is narrower compared to Visayas andMindanao), which is relevant to the duration of interaction between topography and the TC. Wu and Choy(2015) noted that the TC’s translational speed accelerates (decelerates) as they approach (depart from) Luzon
Island, which agrees with the behavior of TCs landfalling in Visayas; on the other hand, the opposite wasobserved for TCs passing through Mindanao, where
the translational speed decreases as they approach anddepart the island. Compared to Luzon and Visayas,
Mindanao has a wide terrain with more complex topography, considering the presence of multiple mountains and mountain ranges, which may have caused alarger decrease in the energy budget of the TC; thus,
there is a consistent deceleration of TCs as they traversed the island. More specifically, TCs take about
6–9 h to traverse Luzon, 17–30 h to traverse Visayas,
and 7–14 h to traverse Mindanao. Furthermore, while
there is a slight tendency for TCs to deflect leftward
upon leaving Luzon Island as manifested by the significant negative correlation between DP and AP, there

is a significant positive correlation found between
the deflection angles of TCs before and after crossing
Mindanao, such that a TC deflected to the right (left)
before landfall is likely to deflect to the right (left) after
crossing Mindanao, while no significant linear relationship in terms of deflections has been observed for
TCs in Visayas. Unlike Luzon and Mindanao, which
account for one island each, Visayas is a sea-island mix(i.e., there may have been deflections after traversing
each individual island, which are not considered in thisstudy). When examining the TC behavior from AP − 6
to AP − 24, landfalling TCs over Mindanao that were
deflected to the right at AP are mostly intense TCs thathave generally consistent translational speeds at all
approaching points. For Visayas, TCs undergoing transient deflection tend to be more intense, but TCs thathave a consistently greater translational speed are theTCs that are deflected to the right at AP. An extensive
study of TCs crossing the Visayas group must be done
to fully define how it affects TCs in terms of deflections.

Petilla et al. Progress in Earth and Planetary Science(2023) 10:32

Geography plays a critical role in TC behavior as
it passes through the Philippine Archipelago (Brand
and Blelloch 1973; Tang and Chan 2014; Racoma et al.
2016; Yang et al. 2022). To reiterate, the main landmassesof the Philippines, Luzon Island, Visayas Islands, andMindanao Island are dissimilar. More specifically, threemountain ranges exist in Luzon Island, while Mindanao Island has a complex topography with mountainous regions and is located closer to the equator. Lastly,
Visayas is a sea-island mix found in between Luzon andMindanao.

4 Summary and concluding remarks
This study investigated the climatology and characteristics of landfalling TCs over central and southern Philippines from 1979 to 2020. A total of 8 TCs in Mindanao
and 39 TCs in Visayas were examined in terms of thechanges in tracks, intensities, and translational speeds
as they interacted with the islands’ topography. It wasobserved that TCs have a greater frequency to makelandfall in Visayas and Mindanao during the NDJFM
season, which are considered as the off TC season.
More specifically, there were 6 TCs that made landfall
in Mindanao in December, while there were 10 and
15 TCs that made landfall in Visayas in the months ofNovember and December, respectively. Thus, this isessential information for scientists, engineers, and first
responders to anticipate the increased TC occurrence
during the latter part of the year.
Furthermore, results also show that TCs generally
weaken as they traverse through Mindanao and Visayas.
For TCs traversing through Mindanao, the decreased
intensity as represented by the change in the maximum sustained winds (MSW) of the TCs with at least
Typhoon (TY) intensities is about 23.33 kts on average,
while TCs with intensities of TS are less affected andhave an average decrease of about 6.67 kts. For TCs traversing through Visayas, the average decrease in MSW
with TS intensities is about 8.13 kts. Additionally, TCs
classified as TY, on average, decrease in intensity by
about 24.29 kts. These decrease in intensities may becaused by friction, changes in the latent heat supply,
and a change of moisture supply over land as noted
in previous studies (e.g., Brand and Blelloch 1973;
Wu and Choy 2015). Recall that TCs passing throughVisayas take about 12 to 36 h, which may explain thegreater magnitude of the intensity drop with respect to
Mindanao.
Only 1 TS increased in intensity by 5 kts, which is
NELL (1993), while 2 TSs maintained their intensities, which are JANGMI (2014) and TEMBIN (2017).
For Visayas, 7 TSs intensified, on average, by about 7.5

Page 21 of 23

kts which shows a 14.1% at AP, respectively. The maintenance or intensification of TCs after landfall can be
attributed to weak low-level temperature gradients, sufficient soil moisture, and enhanced surface latent heat
flux (Sugino and Satomura 2010; Andersen and Shepherd
2013; Andersen et al. 2013; Shepherd et al. 2021).
The TCs moving across Mindanao and Visayas decelerate as they approach and move away from Mindanao.
As the TCs approach (move away from) land, there is adecrease (increase) in the moisture and heat from theocean and there is an increase (decrease) in surface friction causing deceleration (acceleration) before (after)
landfall. The translational speed exhibited by landfalling
Visayas TCs is similar to the landfalling Luzon TCs from
Wu and Choy (2015).
Comparing the results from Wu and Choy (2015) overLuzon Island, we found a similar significant intensity
drop upon landfall over Visayas and Mindanao. In termsof translational speed, the results contradict between
Luzon and Visayas-Mindanao wherein TCs accelerate(decelerate) as they approach (leave) Luzon Island, while
TCs for both Visayas and Mindanao decelerate as they
approach and depart the islands. In terms of TC deflection, weaker TCs have a greater tendency to be deflected
at AP compared to stronger TCs that are landfalling in
Visayas and Luzon. This contradicts with the findingsin Mindanao where the stronger TCs have the greater
tendency to be deflected at AP. While no correlation interms of TC deflection has been found between DP and
AP, a similar (opposite) direction of deflection has been
observed in Mindanao (Luzon).
The present study was also able to show that weaker
TCs in Visayas appear to be deflected more at both DP
and AP compared to stronger TCs, which would indicatethat topography is more effective in deflecting weakerTCs (Wang et al. 1999; Wu and Choy 2015). However,this contradicts the findings in Mindanao where stronger
TCs have a greater tendency to be deflected at AP thanweaker TCs. Tang and Chan (2014) attributed the rightward deflection of TCs prior to landfall over Luzon as aresult of the convergence over the Philippine archipelagothat weakens an anticyclonic gyre. These terrain-induced
gyres were found over the mountains of Luzon, which
pushes the TCs in a northeast direction.
This study only examined the characteristics of landfalling TCs over Mindanao (southern Philippines) and
Visayas (central Philippines). However, a lot of issues stillneed to be addressed in future studies. For example, idealized numerical simulations such as those by Tang andChan (2014) may help further elucidate how Mindanao
Island or Central Visayas topography interacts with TCs
crossing it. More specifically, further investigation for thePetilla et al. Progress in Earth and Planetary Science(2023) 10:32

existence of terrain-induced gyres may possibly explain
the northeastward bias of TCs (Tang and Chan 2014).
So far, only one study examined the impact of Mindanao
Island’s mountains on the TC-induced rainfall (i.e., Minamide and Yoshimura 2014). We expect that more insights
will be gained from high-resolution numerical model
simulations on topography-TC interactions. Anotherlimitation of this study is that WMO reports the intensities of the TCs with an interval of 5 and may reduce theaccuracy and that it does not provide TC intensity below
30 kts.
Abbreviations
AP	Approaching point
C1	Category 1
C2	Category 2
C3	Category 3
C4	Category 4
C5	Category 5
CI	Confidence intervalDP	Departing pointJJASO	June, July, August, September, October
WMO	World Meteorological Organization
LP	Landing point
MSW	Maximum sustained wind speed
NDJFM	November, December, January, February, and March
RI	Rapid intensification
RW	Rapid weakeningTC	Tropical cyclone
TD	Tropical depression
TS	Tropical storm
TY	Typhoon
WP	Western PacificSupplementary Information
The online version contains supplementary material available at https://​doi.​
org/​10.​1186/​s40645-​023-​00563-1.
Additional file 1: Figure S1. TC tracks of landfalling Mindanao TCs during
JJASO and NDJFM seasons. The red crosses indicate the genesis location.
Figure S2. TC tracks of landfalling Visayas TCs during JJASO and NDJFM
seasons. The red crosses indicate the genesis location.
Acknowledgements
J. Matsumoto was supported by the Tokyo Human Resources Fund and Tokyo
Metropolitan Government Advanced Research Grant Number (H28–2) at
Tokyo Metropolitan University from the Tokyo Metropolitan Government.
Part of this study was supported by Grant-in-Aid for Scientific Research(No. 19H00562; PI Jun Matsumoto, 17H06116; PI Tomoko Shiroyama of the
University of Tokyo, and 20H01386; PI Yoshiyuki Kajikawa of Kobe University).
This research was also supported by the Science and Technology ResearchPartnership for Sustainable Development (SATREPS; No. JPMJSA1612) fundedby the Japan Science and Technology Agency (JST) and Japan International
Cooperation Agency (JICA) funded by the JST (PI Yukihiro Takahashi of Hokkaido University). L.M.P. Olaguera was supported by the Follow-up Research
Fellowship for Former International Students grant of the Tokyo Metropolitan
University. C.E.R. Petilla and L.P.S. Tonga are grateful for the scholarship provided by the Department of Science and Technology-Science Education Institute (DOST-SEI) and the Office of Admission and Aid of the Ateneo de Manila
University (ADMU) during their undergraduate studies in the Department of
Physics in ADMU. The authors are also grateful to Regional Climate Systems of
the Manila Observatory’s project: High-definition Clean Energy, Climate, andWeather Forecasts for the Philippines for sponsoring this research.

Page 22 of 23

Author contributions
CERP, LPST, and LMPO proposed, analyzed the data, and drafted the manuscript. JM helped in the interpretation, review, and writing of the manuscript.
Funding
The authors declare that there is no funding support used in this study.
Availability of data and materials
The authors declare that they only used open access data in this paper. Specifically, the tropical cyclone data were provided by the Joint Typhoon Warning Center of the US Navy and can be accessed here: https://​www.​metoc.​navy.​
mil/​jtwc/​jtwc.​html?​best-​tracks.

Declarations
Ethics approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
Author details
1
Department of Physics, Ateneo de Manila University, Loyola Heights,
1108 Quezon City, Philippines. 2 Regional Climate Systems Laboratory, Manila
Observatory, Quezon City, Ateneo de Manila University Campus, Loyola
Heights, 1108 Quezon City, Philippines. 3 Department of Geography, Tokyo
Metropolitan University, 1‑1 Minami‑Osawa, Hachioji‑Shi, Tokyo 192‑0397,
Japan. 4 Center for Coupled‑Ocean‑Atmosphere Research, Japan Agency
for Marine Earth Science and Technology, Yokosuka, Kanagawa 237‑0061,
Japan.
Received: 11 August 2022 Accepted: 11 June 2023

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