Tropical storms form over warm ocean waters through the process of convection where warm, moist air rises, cools and condenses, releasing heat. For a tropical storm to form, specific conditions are needed - sea surface temperatures above 26°C, a moist atmosphere, location away from the equator, a pre-existing low pressure disturbance, and little wind shear between the surface and upper atmosphere. Tropical storms typically form within bands of latitude between the equator and 30 degrees in each of the world's seven tropical cyclone basins during their respective peak seasons.

3. Tropical Storm
A tropical cyclone is a storm system with a low-pressure
centre. However, while typical Canadian lows and
storm systems are fueled by a battle between cold and
warm air, tropical cyclones are fueled by a different
process. This process involves water being converted
to water vapour, which is then converted back to liquid
water

4. Warm, moist air moves over the ocean.

5. Water vapour rises into the atmosphere

6. As the water vapour rises, it cools and
condenses into liquid droplets

7. Condensation releases heat into the
atmosphere, making the air lighter

8. The warmed air continues to rise, with moist air
from the ocean taking its place and creating more
wind

9. Conditions Needed For Tropical
Cyclones To Form
 Warm ocean waters to fuel the tropical cyclone.
Studies have shown that sea surface temperature must
be at least 26°C, and this temperature is actually
required to a depth of at least 50 m. That’s why tropical
cyclones can’t form outside of the tropics--water
temperatures are too cold.

10.  A warm, moist tropical atmosphere that
encourages thunderstorm development.
Thunderstorm development is the foundation of the
latent heat release process, the driving mechanism of
tropical cyclones.
 More than 500 km (about 5° latitude) away from
the equator. This is important because the Coriolis
force--the apparent force of the rotating earth--is
necessary to generate the rotation of the growing
disturbance, and without it a low pressure cannot be
maintained. The Coriolis force is slight near the
equator and gets stronger towards the poles.

11.  A pre-existing near-surface disturbance, low-pressure
area or region of convergence. This is necessary because
tropical cyclones cannot generate spontaneously and they
require a trigger mechanism to begin drawing air inwards
at the lowest levels of the atmosphere.
 Little to no vertical wind shear between the surface
and the upper troposphere (the upper part of the
atmosphere where weather occurs, just below the
stratosphere). Vertical wind shear is simply a change of
wind speed or direction with increasing altitude. Large
vertical wind shear disrupts a growing disturbance and can
prevent a tropical cyclone from forming. If a tropical
cyclone has already formed, large vertical wind shear can
weaken or destroy it by interfering with the processes of
deep convection (overturning air) around the cyclone
centre by things such as tilting them over and poking holes
in the warm core.

12. While these conditions are needed to create a tropical
cyclone, it does not mean that they are enough to
create one. Often all of these conditions exist, yet a
tropical cyclone does not form. This is part of the
challenge in forecasting when a tropical cyclone will
develop--a process known as tropical cyclogenesis.

13. When and where tropical cyclones
form
The table below outlines the seven basic tropical cyclone
“basins,” the times of year when each basin is active,
and the names given to the strongest tropical cyclone.
Note on the map that tropical cyclones don’t form near
the equator (the Coriolis force is too weak to initiate
rotation) and they don’t form far away from the
equator (water temperatures are too cold). Therefore,
tropical cyclones typically form within a band of
latitudes.

14. Map
Reference
Ocean Basin Season Season Peak Name When
Winds Exceed
118 km/h
1. N Atlantic Ocean
(includes Caribbean
and Gulf of Mexico)
June to
November
September Hurricane
2. NE Pacific
(east of dateline)
mid May to
mid
November
Late August to
early September
Hurricane
3. NW Pacific Ocean
(west of dateline,
includes S China Sea)
All year Late August to
early September
Severe Cyclonic
Storm
4. N Indian Ocean
(includes Bay of
Bengal, Arabian Sea)
April to June
and October
to December
May and
November
Tropical
Cyclone

15. Map Reference Ocean Basin Season Season Peak Name When
Winds Exceed
118 km/h
5. SW Indian
Ocean
October to May mid January to
early March
Tropical
Cyclone
6. SE Indian
Ocean
(north of
Australia)
October to May mid January to
early March
Severe Tropical
Cyclone
7. SW Pacific
Ocean
All year February to
early March
Severe Tropical
Cyclone