THE CASE STUDY OF TYPHOON SURIGAE
(BISING)
Philippines sits on the Pacific typhoon belt. An area where
conditions support the formation of tropical storms.
That is why, the Philippines is a typhoon-prone country
that deals with 20 typhoons per year on average.
What are typhoons – and how do typhoons form?
Typhoons, the name for hurricanes that hovers in the
Northwest Pacific Ocean. Typhoons use warm and humid
air as fuel, which is why they only occur near the equator. A
typical typhoon forms due to high temperatures around the
sea surface, as a result of which water evaporates and
becomes warm and humid air. This air moves away from the
surface, leaving an area of lower air pressure below.
Air from surrounding areas with higher air pressure pushes
into this lower pressure area. The new air then becomes
warm and rises as well. As this process repeats, clouds are
formed when the moist air cools off, and when the rain falls,
wind increases, hence the thunderstorm.
This is where the Coriolis force comes into play. The Coriolis
force is caused by the Earth’s rotation that deflects moving
objects to the right in the Northern Hemisphere and to the
left in the Southern Hemisphere.
Development of the Typhoon Surigae (Bising)
As typhoons form over warm ocean waters, one such storm that
emerged was Typhoon Surigae.
Typhoon Surigae began to form in mid-April 2021, with
atmospheric convection developing approximately 1,150 km
south of Guam. By April 10, the disturbance acquired rainbands
and was moving west-northwest. It was classified as a tropical
depression on April 12, and by April 13, it strengthened to a
tropical storm, named Surigae on April 14.
Surigae rapidly intensified into a typhoon by April 16, just north
of Palau, and entered the Philippine Area of Responsibility
(PAR) on the same day, receiving the local name "Bising." The
typhoon made landfall and had significant impacts on the
Philippines, including strong winds and heavy rainfall, leading
to widespread damage. Surigae experienced explosive
cyclogenesis, with maximum sustained winds of 130 km/h (80
mph) and a central pressure dropping to 944 hPa (mbar). The
system weakened as it moved eastward, undergoing center
reformation on April 30. Surigae's remnants continued to
weaken and were ultimately absorbed into another extratropical
cyclone on May 2.
With the added force, a thunderstorm starts to rotate,
which explains why a typhoon spirals in the anticlockwise
direction when observed in the Northern Hemisphere, and
clockwise in the Southern Hemisphere. By the time it
reaches 119km/h, it is officially a tropical cyclone or
typhoon.
As mighty as the typhoon can be, it still loses its strength.
For instance, if it reaches land, it will weaken and begin to
collapse rapidly. This is because without the constant flow
of rising moist and warm air, typhoons lose the energy that
powers the process.
Impact and Aftermath of Typhoon Surigae
Typhoon Surigae struck the Philippines in April 2021,
resulting in at least 10 deaths, affecting over 158,000 people
and displacing over 75,000 people. It also causes a significant
flooding in 22 barangays in Region VIII, with a total of
40,658 families (158,112 persons) were affected across 758
barangays, with 8,585 families (34,560 persons) seeking
shelter in 456 evacuation centers and 10,515 families (40,522
persons) staying with relatives or friends.
The storm damaged 520 houses (52 completely destroyed
and 468 partially damaged), rendered two road sections and
one bridge impassable in Region VIII causing at least ₱272.8
million (US$5.67 million) in damage. The storm led to
widespread flooding and landslides, particularly in Eastern
Visayas and parts of Luzon, complicating relief efforts and
highlighting the need for improved disaster preparedness
and infrastructure resilience in the region. Humanitarian
responses included food, water, and medical aid, but many
communities faced long-term recovery challenges due to the
extensive destruction.