Cyclones

 Cyclones are huge revolving storms caused by
winds blowing around a central area of low
atmospheric pressure.
Wind blows anti-clockwise in the
NH and clockwise in the SH
Typhoon- termed used when it
formed in the Pacific ocean
Hurricane- termed used when it
formed in the Atlantic ocean
Cyclone- termed used when it
formed in the southern ocean and
Indian ocean
Willy-willy- termed used in Australia

 Classification of cyclone according to synoptic
scale
 1. Polar cyclone (polar regions, vast)
 2. Polar lows (polar regions, short)
 3. Extratropical cyclone (mid-latitude cyclone)
 4. Subtropical cyclone (between the equator
and 50o N and S)
 5. Mesocyclone (associated with tornado
formation)
 6. Tropical cyclone (tropics)

 Tropical cyclone is non-frontal synoptic scale low-
pressure system over tropical waters with
organized convection (i.e. Thunderstorm activity)
and cyclonic surface circulation.
This low pressure creates
violent storms that are
characterised by winds
over 100km/h and heavy
rainfall.
They have caused the
loss of life on a number of
occasions due to there
intensity.

 TC has synoptic scales of 100’s km

 Average number of typhoons in the different areas of the world

 1. Warm ocean waters at least (26.5°C) to provide the
heat.
 2. Availability of moisture. Moisture is necessary for
providing latent heat of condensation.
 3. Coriolis force to provide the rotation. (they do not
form within 5o of the equator due to the negligible CF
there).
 4. A seedling or cyclonic weather disturbance with
extra cloud cover.
 5. Almost uniform large scale wind with little vertical
shear to allow heat to accumulate (less than 10m/s).
 6. An exhaust system consisting of a divergent upper
level disturbance.

 Peak intensity of a typhoon is the maximum intensity
the storm reaches during its entire lifetime.
 It results from an accumulation of intensification, which
is equivalent to speed being an accumulation of
acceleration.
 Cyclone can grow depends on two oceanic
factors:
 pre-storm sea surface temperature
 difference in temperature between the surface and
subsurface.
 A warmer sea surface generally provides more
energy for storm development and thus favors higher
intensification rates.

 Evaporation
increases rapidly
as temperature
increases.
 Evaporation=
energy in the form
of latent heat that
fuels the cyclone.

 Orange/yellow regions- tropics between June and
December

 Cold currents
 Without the Coriolis force, surface winds cannot
gain sufficient rotation to converge and the low
pressure of the disturbance cannot be maintained.
 Large values of vertical wind shear disrupt the
formation of a tropical cyclone by interfering with
the organization of deep convection around the
cyclone center.
◦ Wind shear- refers to a change in wind speed or
direction with height in the atmosphere.

Dry air from Sahara can
weaken storms
Dust blocks the sun and
cools the ocean

 Eye: A region 30-65 km in diameter found at the center where skies
are often clear, winds are light, and the storm's lowest
pressure readings are obtained.
 Eye Wall: A ring of cumulonimbus clouds that swirl around the eye.
The heaviest precipitation and strongest winds are found here.
 Spiral Rainbands: Bands of heavy convective showers that spiral
inward toward the storm's center. Thunderstorms are observed
here.

 In the “eye”, air is slowly sinking
(causes compressional warming)
and “warm core”
 The eyewall has a net upward
airflow as a result of numerous
updrafts and downdrafts
 Near the top of the eye-wall
clouds relatively dry air flows
outwards from the center. This
diverging air aloft extending
outwards for 100s km. As the
outflow reaches the cyclones
edges it sinks.
 In the spiral rain bands, air
converges at the surface,
ascends through these bands,
diverges aloft, and descends on
both sides of the bands.

 Strong pressure gradient within
eyewall
 Responsible for strong typhoon
winds. Speed is fastest on
“right” side of the typhoon:
sum of rotational and
forward velocity.
 Rain occurs in eyewall
(heaviest) and spiral rainbands.
 Temperature increases in the
eye because of descending air.

 Tropical Disturbance:
The birth of a hurricane, having only a slight circulation with no
closed isobars around an area of low pressure.
 Tropical disturbances commonly exist in the tropical trade winds at any
one time and are often accompanied by clouds and precipitation.
 Tropical Depression
A tropical cyclone in which the maximum sustained wind speed less
than 64 KPH. Depressions have a closed circulation

 Tropical Storm
A tropical storm has a maximum sustained surface wind speed
between 64 KPH and 117 KPH . The convection in tropical
storms is usually more concentrated near the center with outer
rainfall organizing into distinct bands.
 Typhoon or Hurricane
Typhoon has a maximum winds exceed 117 KPH.

 Tropical Depression (TD) has maximum sustained winds of up to
61 kilometers per hour, equivalent to 33 nautical miles per hour or
more.
Tropical Storm (TS) packs 62 to 117 kilometers per hour.
Meanwhile, a Severe Tropical Storm will only be applicable for the
International Warning for Shipping, and will not be used for general
public dissemination unlike the other categories.
Typhoon (TY) is used in identifying a tropical cyclone with wind
speeds 118 to 220 kilometers per hour or 64 to 120 knots.
Super Typhoon (STY) has maximum sustained winds of more than
220 kilometers per hour. STY is as powerful as 120 nautical miles
per hour or more.

 1. Formative stage
 2. Immature stage
 3. Mature stage
 4. Decay stage
 Formative (Incipient) Stage
◦ The tropical cyclone starts as a low pressure system with
cyclonic wind circulation. At the formative stage, the
surface pressure at the center of the system falls to about
1000 mb The wind speed at this stage is below 34 kt.
Clouds and rainfall are of disorganized squall type.
◦ Cyclogenesis- refers to the process of cyclone
formation and intensification

 Formation process
 Surface water evaporates and is convected
upward
 Air rises and diverges; some air is forced towards
the eye center, where it sinks
 Compressional heating in the eye creates the
warm core and clear conditions
 Divergence aloft and warmer sir results in lower
surface pressure
 Increased surface pressure gradient yields
increased surface winds
 Evaporation increases and the cycle strengthens

 Immature Stage
 At the immature Stage there is a further
drop in surface pressure at the centre of
the system (to below 1000 mb). The
wind speeds increase to hurricane force
(about 64 kt). Clouds and rainfall are
more organized and spiral inwards. The
area involved is still relatively small
(radius is 30 to 50 km)
 Mature Stage
At the mature stage the surface pressure at the center of remains
low but steady (pressure averages 950 mb; values of about 900 mb
have been recorded. The lowest recorded pressure was 870 mb).
The wind speed reach that of the hurricane force (~64 kt), but is
more steady.There is bad weather. (Rainfall may reach 10 – 20 cm
in 3 hours.). The area involved increases (radius ranges from 200 to
1000 km; some systems may reach radii of 1700 km).

 Decaying Stage
 Tropical cyclones decay due to;
 (a) Frictional dissipation (by
surface features),
 (b) Disruption of vortex, (by
terrain or encounter with
westerlies),
(c) Lack of sufficient moisture as they move inland
(d) movement to places of cold sea surface
temperatures
If tropical cyclones move into the extra-tropics they
encounter westerlies. They may dissipate or be
transformed into extra-tropical cyclones.
Typical lifetime is less than a week.

 The lifetime of a cyclone is
determined by how
favourable the atmospheric
environment is, movement,
sea surface temperatures.
 While most cyclones
undergo a life-cycle of 3-7
days some weak ones only
briefly reach gale force
while others can be
sustained for weeks if they
remain in a favourable
environment.
 The longest being
Hurricane Ginger (1971)
that lasted for 30 days.

Size descriptions of tropical cyclones
ROCI Type
Less than 2 degrees latitude Very small/midget
2 to 3 degrees of latitude Small
3 to 6 degrees of latitude Medium/Average
6 to 8 degrees of latitude Large
Over 8 degrees of latitude Very large
There are a variety of metrics commonly used to measure storm
size. The most common metrics include the radius of maximum
wind, the radius of 34-knot wind , the radius of outermost
closed isobar (ROCI), and the radius of vanishing wind
1o lat= 60 nm

 The Philippine Area of
Responsibility (PAR) is
bounded by the black
lines joining the following
points:
25°N - 120°E
 25°N - 135°E
 5°N - 135°E
 5°N - 115°E
 15°N - 115°E
 21°N - 120°E.


 Public Storm Warning Signal Number 1
◦ A tropical cyclone may threaten or affect the locality. Winds from 30-60 KPH may
be expected in at least 36 hours.
◦ A tropical cyclone may threaten the locality. Winds between 61-120 kph may be
expected in at least 24 hours.
◦ A tropical cyclone will affect the locality. Winds of 121 - 170 Kph may be expected
in at least 18 hours.
◦ A very strong typhoon will affect the locality. Very strong winds of more than 171-
220 kph may be expected in at least 12 hours.
◦ Super typhoon. Very strong winds over 220 kph may be expected in at least 12
hours.

PSWS LEAD TIME
(hours)
WINDS
(kph)
IMPACTS OF
THE WIND
1 36 30-60 No damage to
very light damage
2 24 61-120 Light to moderate
damage
3 18 121-170 Moderate to
heavy damage
4 12 171-220 Heavy to very
heavy damage
5 12 More than 220 Very heavy to
widespread
damage

 Winds of 30-60 kph is expected.
 Sea condition
◦ Wave Height: 1.25-4.0 meters
 Damage to structures
Very light or no damage to high risk
structures,
Light to medium and low risk structures
Slight damage to some houses of very
light materials or makeshift structures in
exposed communities.
 Damage to vegetations
Some banana plants are tilted, a few
downed and leaves are generally
damaged
Twigs of small trees may be broken.
Rice crops, however, may suffer significant
damage when it is in its flowering stage.

 Winds of greater than 61 kph and up to
120 kph may be expected in at least 24
hours.
 Sea condition
 Wave Height: 4.1-14.0 m
Storm surge possible at coastal areas
Damage to structures
Light to Moderate damage to high risk
structures;
· Very light to light damage to medium-risk
structures;
· No damage to very light damage to low risk
structures
Unshielded, old dilapidated schoolhouses,
makeshift shanties, and other structures of light
materials are partially damaged or unroofed.
Most banana plants, a few mango trees, ipil-ipil
and similar types of trees are downed or broken
Some coconut trees may be tilted with few others
broken
Rice and corn may be adversely affected
Considerable damage to shrubbery and trees with
some heavy-foliaged trees blown down.

 Winds of greater than 121 kph up to
170 kph may be expected in at least 18
hours.
 Sea condition
 Wave Height: > 14.0 meters
Storm surge possible at coastal areas
Heavy damage to high–risk structures;
· Moderate damage to medium- risk
structures;
· Light damage to low-risk structures
Increasing damage to old, dilapidated
residential structures and houses of light
materials (up to 50% in a community)
Almost all banana plants are downed, some
big trees (acacia, mango, etc.) are broken or
uprooted,
Dwarf-type or hybrid coconut trees are tilted
or downed
Considerable damage to shrubbery and trees
with heavy foliage blown off; some large trees
blown down.

 Very strong winds of greater than 171
kph up to 220 kph may be expected in at
least 12 hours.
 Sea condition
 Wave Height: more than 14.0 meters
Storm surge2-3m possible at coastal areas
Very heavy damage to high –risk structures
· Heavy damage to medium risk structures;
· Moderate damageto low-risk structures
Considerable damage to structures of light
materials (up to 75% are totally and partially
destroyed); complete roof structure failures.
There is almost total damage to banana
plantation,
Most mango trees, ipil-ipil and similar types of
large trees are downed or broken.
Coconut plantation may suffer extensive
damage.
Rice and corn plantation may suffer severe
losses.

 more than 220kph
Expected in12hrs on 1stissuance.
 Sea condition
 Wave Height: more than 14.0 m
Storm surge more than 3 meters possible at
coastal areas
Widespread damage to high-risk
structures
· Very heavy damage to medium-risk
structures
· Heavy damage to low-risk structures;
Almost total damage to structures of light
materials, especially in highly exposed coastal
areas.
Total damage to banana plantation
Most tall trees are broken, uprooted or
defoliated;
Coconut trees are stooped, broken or uprooted.
Few plants and trees survived

 Average number of
typhoons per year-
20
 Months of July-
August and
September have the
highest average
number of typhoons
(>3)
 Typhoons cause
more deaths (68%)
0.5
0.3 0.3 0.4
0.9
1.5
3.4 3.4 3.1
2.7
2.3
1.4
0
1
2
3
4
5
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
NUMBER OF DEATHS
Landslides
(2%)
Floodings
(5%)
Earthquake &
Others(25%)
Tropical Cyclones (68%)

 1. Super Typhoon Haiyan (international name: Yolanda), the strongest
storm ever recorded on land, destroys entire towns across the central
Philippines on November 8, 2013. When the government stopped its count
months later, more than 7,350 people were listed as dead or missing.
 2. Tropical Storm Uring (international name: Thelma) unleashes flash
floods on the central city of Ormoc on Leyte island on November 15, 1991,
killing more than 5,100.
 3. Typhoon Pablo (international name: Bopha) smashes into the main
southern island of Mindanao on December 3, 2012. Rarely hit by major
storms, the unprepared region suffers about 1,900 people dead or missing.
 4. Typhoon Nitang (international name: Ike) hits the central Philippines on
August 31, 1984, killing 1,363 people.
 5. Typhoon Sendong ((international name: Washi )hits the northern part of
Mindanao island on December 16, 2011, killing at least 1,080 people.

 6. Floods and landslides unleashed by Typhoon Trix kill 995 people
in the Bicol region of the main island of Luzon on October 16, 1952.
 7. Typhoon Amy rakes across the central islands in December
1951, with floods, landslides and a massive storm surge killing 991
people.
 8. Typhoon Sisang (international name: Nina) hits the eastern city
of Legaspi on November 25, 1987, triggering giant storm surges
and unleashing mudslides down Mayon volcano that claim 979
lives.
 9. Typhoon Frank (international name: Fengshen) tracks an erratic
and destructive path across the central islands and nearby areas
from June 20, 2008, killing 938 people.
 10. Typhoon Rosing (international name: Angela), with gusts of up
to 260 kilometers an hour, causes carnage in Bicol and later Manila
from November 2, 1995, killing 936 people.

 interaction between two typhoons having a certain distance (about
1300-1400 km depending on the sizes of the cyclones) from each
other and begin to rotate about a common midpoint.
Recently, the definition involved two
or more typhoons that interact from
each other.
Fujiwhara effect' is named after Dr.
Fujiwhara of Japan. He discovered
interaction between two cyclonic
vortices when they were close to each
other.
The point is determined by the relative
mass and the vortices intensity. The
smaller typhoon engaged in such
mutual orbiting always moves faster
than its bigger counterpart. Some
interactions eventually cause the two
typhoons to spiral into the center and
merge.

When two vortices spinning counter-clockwise
draw near and one of the vortices is bigger than
the other, they start spinning around each other
for a brief time with the larger one dominating.
Gradually the lesser of the two gets trapped in
the circulation of the larger one and absorbed.
When comparable vortices spin in opposite
directions, one clockwise, one counter-
clockwise, they press each other away when
they near.

 Cyclone interactions are broken down into four
categories or steps:
 1. Approach and Capture
 2. Mutual Orbit
 3. Merger
 4. Escape.

 Weather stations
 Buoys
 Ships
 Radar
 Aircraft Reconnaissance
 Visible/Infrared Satellites
 Microwave satellites
 Satellite estimates account for vast majority of the
record

1. Tropical cyclones out at sea cause large waves, heavy rain, and high
winds, disrupting international shipping and, at times, causing
shipwrecks.
2. Tropical cyclones stir up water, leaving a cool wake behind them,
which causes the region to be less favourable for subsequent tropical
cyclones.
3. On land, strong winds can damage or destroy vehicles, buildings,
bridges, and other outside objects, turning loose debris into deadly
flying projectiles.
4. The storm surge, is typically the worst effect from landfalling tropical
cyclones, historically resulting in 90% of tropical cyclone deaths.
5. The broad rotation of a landfalling tropical cyclone, and vertical wind
shear at its periphery, spawns tornadoes.
6. Tropical cyclones have been responsible for the deaths of about
1.9 million people worldwide. Large areas of standing water caused by
flooding lead to infection, as well as contributing to mosquito-borne
illnesses.
7. Tropical cyclones significantly interrupt infrastructure, leading to power
outages, bridge destruction, and the hampering of reconstruction
efforts.

1. Bring precipitation. Rainfall increases groundwater and
the water levels of dams that provide drinking water,
irrigation water and power generation.
2. Rains mean water for plants. About 50% of our water
supply comes from rainfall brought by tropical cyclones.
3. Decreases the level of pollutants.
4. Tropical cyclones also help maintain the global heat
balance by moving warm, moist tropical air to the middle
latitudes and polar regions.
5. The storm surge and winds of hurricanes may be
destructive to human-made structures, but they also stir
up the waters of coastal estuaries, which are typically
important fish breeding locales.
6. Tropical cyclone destruction spurs redevelopment,
greatly increasing local property values.

 Tropical cyclones are named to provide ease of communication between
forecasters and the general public regarding forecasts, watches, and warnings.
 1890s - Australian weatherman Clement Wragge started giving female names
to tropical cyclones.
 1900s- male names were also given to typhoons that formed elsewhere.
 1912 - a number of US Air Force pilots, US Navy soldiers, and weather
forecasters named storms with supposed distinction after their wives and
girlfriends.
 From 1963 to 2001, the Philippines had adopted a similar naming system using
Filipino women's names starting from A to Y and ending with -NG or -ING like
“Auring,” and “Yayang.”
These names had been used according to the 19 letters of the Filipino alphabet
until the then Department of Education, Culture and Sports, now Department of
Education, modernized it bringing it up to 26 letters including F, J, N, Q, X, and
Z.
 1998 – Pagasa held a contest to replace the old-sounding female nicknames.
 2001- adopted the new list of names (old names were replaced particularly
those who claimed more lives)

1 2 3 4
2009
2013
2017
2021
2010
2014
2018
2022
2011
2015
2019
2023
2012
2016
2020
2024
AURING
BISING
CRISING
DANTE
EMONG
FERIA
GORIO
HUANING
ISANG
JOLINA
KIKO
LANNIE
MARING
NANDO
ODETTE
PAOLO
QUEDAN
RAMIL
SALOME
TINO
URDUJA
VINTA
WILMA
YASMIN
ZORAIDA
AGATON
BASYANG
CALOY
DOMENG
ESTER
FLORITA
GARDO *
HENRY
INDAY
JOSIE *
KARDING
LUIS
MAYMAY *
NENENG
OMPONG
PAENG
QUEENIE
ROSITA *
SAMUEL *
TOMAS
USMAN
VENUS
WALDO
YAYANG
ZENY
AMANG
BETTY
CHEDENG
DODONG
EGAY
FALCON
GORING
HANNA
INENG
JENNY
KABAYAN
LIWAYWAY *
MARILYN
NONOY
ONYOK
PERLA
QUIEL
RAMON
SARAH
TISOY
URSULA
VIRING
WENG
YOYOY
ZIGZAG
AMBO
BUTCHOY
CARINA
DINDO
ENTENG
FERDIE
GENER
HELEN
IGME
JULIAN
KAREN
LAWIN
MARCE
NINA
OFEL
PEPITO
QUINTA
ROLLY
SIONY
TONYO
ULYSSES
VICKY
WARREN
YOYONG
ZOSIMO

1 2 3 4
ALAMID
BRUNO
CONCHING
DOLOR
ERNIE
FLORANTE
GERARDO
HERNAN
ISKO
JEROME
AGILA
BAGWIS
CHITO
DIEGO
ELENA
FELINO
GUNDING
HARRIET
INDANG
JESSA
ABE
BERTO
CHARO
DADO
ESTOY
FELION
GENING
HERMAN
IRMA
JAIME
ALAKDAN
BALDO
CLARA
DENCIO
ESTONG
FELIPE
GARDO
HELING
ISMAEL
JULIO
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