ATOC 181 Lecture 17: Lecture 17
7 Jun 2018
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LESSON 17
TROPICAL CYCLONES
Tropics
• Region around the equator, between the tropic of Cancer and Capricorn.
• Good reason to bother about them here in Canada: do receive quite a lot of them
• The majority of major hurricanes (cat 4 and 5): East coast of North America is receiving quite a lot of
them.
o Can cause damages
• Are differences between tropical cyclones when in intertropical region and when they reach us here in
Canada
Introduction
• Amongst the most powerful and destructive meteorological systems on Earth
• 80 to 100 develop globally, over 7 large tropical basins each year
o Eastern Pacific
o Atlantic
o Western North pacific
o South Pacific
o South Indian
o North Indian
o Northwest Australia
• many of these make landfall and can cause considerable damages
o high winds, surges and heavy rain
• Ex: Camille in 1969 = category 5 (highest category): did lot of damages
• Destructive of strong winds and rain that result in flash floods → cause lot of accidents
• Speed of winds can reach more than 200km/h
Tropical Cyclones And Hurricanes
• Tropical hurricanes: generic term
• Hurricanes (east or west coast of the Americas), typhoon (in Japan, China), Bagyo, cyclone: strong
tropical cyclones
o brand term that depends on the region
• Large scale low pressure system
• At surface, pressure can be as low as 870 kPa.
• Originating over (sub)-tropical waters with:
o Lot of convective clouds merging together
o Organized convection (strong ascending air)
o Have cyclonic surface wind rotation/ circulation near the surface
o In Northern hemisphere, cyclonic winds = anti-clockwise direction. In South hemisphere = the
opposite
o Earth rotates counterclockwise no matter if stand at south or north poles
• Have 7 major bases: Western Atlantic (start in June, august-Oct, some in Nov), Eastern Pacific, Americas
• Usually in late summer and early autumn for most basins
• Sub-Indian continent and Australia: use the ter cyclones
• Have some also in Philippines
find more resources at oneclass.com
find more resources at oneclass.com
Hurricanes
• From the Carib Indian word: Huracan
• Derived from a Mayan God who created the world with his breath, blowing on the oceans to create dry
land
• Can have tropical cyclones all year around, but very few in January
• More hurricanes in September than in January in the North Atlantic
Naming Tropical Cyclones
• Relatively recent that given names in our regions
• West-idies: “ait’s aes
o E.g: San Felipe in 1876
• Giving them names because they move all the time, so if refer to a system with coordinates, some time
later, they will be somewhere else.
o need to name it when forecasting them and talking about them
• Australian forecaster early 19th century:
o Politician names
• WWII- US army air Corp and navy-Pacific: girlfriends or wives
• Changed: should also give male name
• Depending on the region, there is a commission at WMO: trying to give names to hurricanes
• After 6 and 7 years: repeat the names in the Atlantic
• Also have retired names
• Here: have alternative male and female name.
o Canada, US and Mexico: francophone, Anglophone or Spanish names
• Atlantic region: flowers, birds, trees
• List of names is defined in advance and is in alphabetical order
• Can happen that at some stage have more hurricanes than have names on the list.
• Some hurricanes that created lot of damages or death, by respect, the name is retired: taken out of the
list
o In 2016, Matthew and Otto were retired.
• List for different regions: for the Atlantic, Pacific, for typhoons, etc
Hurricanes and Canada
• Average number of tropical cyclones each year: 3.4
• Quite different in terms of structure and characteristics once reach Canada. Can be quite as powerful
• 40% of all Atlantic tropical cyclones affect Canada on average.
• 1995: Hurricane Luis, category 3 storm
o reach Avalon Peninsula of Newfoundland
o lot of damages and few deaths
• Sep 1996: Hortense near Cape Breton (NS)
o 120km/h winds, flooding, wind damage and power outages
• Hazel: 30 deaths in Ontario. Went through the Gulf of Mexico and up, create lot of damages, killed due
to flooding
• Well-structured hurricanes
• Movie: the perfect storm
o Storm that hit Canada. Typical tropical hurricane that moves north and combines with a cyclone
= strength of both together created huge damages
• Hurricane Juan: 2003
find more resources at oneclass.com
find more resources at oneclass.com
• 2016: Matthew. Destroys part of Cuba, Haiti, St Martin, hit Canada too. Most dangerous one that we got
• there is one happening right now in the US: lot of snow. 70 million people are affected by it.
Canadian Hurricane Centre
• Website
Necessary Conditions For Hurricanes Development
• Warm ocean waters (larger or equal to 26.5deg over 50m of depth)
o Reason why most hurricanes develop in late spring or in summer
• Instable atmosphere:
o if stable, nothing can go up.
o Unstable: Warm hot water will rise and as it dries, have condensation, latent E will be released
and have creation of strong winds.
o If have warm and hot air below cold air, less dense and tends to go up. When the air near surface
goes up: unstable
• Pre-existing near surface disturbance with sufficient vorticity (rotation) and convergence.
o If no disturbance at surface, difficult for hurricane to start. These disturbances will create the
rotation
• Moist air in lower and mid-troposphere
• Minimum distance of at least 500km from equator.
o Coriolis force: force due to the rotation of the Earth. As a result, if moves in North or southern
hemisphere, will be slowly moving towards the right
o Coriolis force: zero at equator. It depends on distance from Equator and it is maximum at poles.
o If too close to Equator, not enough Coriolis force to
maintain or trigger formation of hurricanes
• Low (less than10m/s) vertical wind shear between surface
and upper troposphere.
o Otherwise, if strong wind shear, tends to cut the top
of developing hurricane and it will never develop;
prevent system of clouds from going up
• Upper tropospheric divergence: tends to pull the air from
the bottom.
o On the other hand, if have convergence at top, air
will meet in the middle as have air going up from
surface as convergence happening there too and
from the top, it is going down.
• All hurricanes form when the temperature of oceans is warm
enough.
o Will reach regions where temperature is colder: will either decay or lose some of their strength.
▪ Explain why few hurricanes develop in January: temperature of oceans not warm enough
• Disturbance at low level: when have difference in temperature, there is convergence, which will create
some rotation in some region. Have systems in Africa where have disturbances and they will go over
water (often the case for generation of tropical hurricanes).
• Intertropical convergence zone: lot of convergence and clouds developing there
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
In northern hemisphere, cyclonic winds = anti-clockwise direction. In 2016, matthew and otto were retired: list for different regions: for the atlantic, pacific, for typhoons, etc. Hurricanes and canada: average number of tropical cyclones each year: 3. 4, quite different in terms of structure and characteristics once reach canada. Went through the gulf of mexico and up, create lot of damages, killed due to flooding: well-structured hurricanes, movie: the perfect storm, storm that hit canada. Typical tropical hurricane that moves north and combines with a cyclone. = strength of both together created huge damages: hurricane juan: 2003, 2016: matthew. Destroys part of cuba, haiti, st martin, hit canada too. Most dangerous one that we got there is one happening right now in the us: lot of snow. Necessary conditions for hurricanes development: warm ocean waters (larger or equal to 26. 5deg over 50m of depth, reason why most hurricanes develop in late spring or in summer.
