tropical cyclones (science v )

THE TROPICAL CYCLONECyclone- is a big whirling mass of

strong winds and rain moving in counter clockwise direction in the northern hemisphere.

All tropical cyclones originate on the western sides of the oceans in the doldrums, the cyclones move westward and away from the equator.

Around the world, tropical cyclones

are called by different names. They come at different times of the year in different places. For example, in our country the tropical cyclones are called “bagyo”. They usually occur from September to November.

By international agreement, tropical cyclones are classified according to speed of the wind. The weakest is called a tropical depression with a maximum wind speed of up to 63 kilometers per hour (kph) or approximately less than 25 mile per hour (mph).

A depression exist when there is low pressure over a large enough area to be plotted on the weather map. The low pressure near the ocean surface draws in warm, moist air which feeds more thunderstorm.

The winds swirl slowly around the lo-pressure area at first. As the pressure becomes even lower, more warm, moist air is drawn in, and the winds blow faster.

A tropical storm has developed when the maximum wind speed is 64 to 118 kph (25 to 75 mph) and with closed isobars.

Near the center of a tropical storm is a column of warm air, The warmer the column is, the lower the pressure at the surface falls. The low pressure, in turn draws more air into the storm. As more air is pulled into the storm, the winds blow harder.

Typhoon- is an intense tropical cyclone with maximum wind speed exceeding 118 kph.

Typhoon or hurricane has a well-developed eye at its center, surface pressure drops to its lowest in the eye.

In the eyewall of the hurricane is its strongest winds. The warm air spirals upward. The speed of the winds in the eyewall is related to the diameter of the eye. A hurricane’s winds blow faster if its eye is small. If the eye widens, the winds decrease.

Very heavy rains fall from the eyewall and bands of the hurricane. The dense clouds that swirl around the eyewall are called rainbands. They can produce more than 5cm of rain per hour that can

cause floods, and flash floods.Image of typhoon Ondoy that brings

a lot of damage and loss lives to people in Metro Manila.

The center of a typhoon is called the eye. It is the center of calm. It is normally 40 km in diameter. In the eye of the storm, warm air is rising and there are no clouds. At the edge of the eye, the speed of the wind is fastest. The eye is characterized by calm air and sunny sky. The distribution of rain is also not uniform. There is no rain in the typhoon’s eye.

In fact, we can see the sun shining if the eye is over us.

There is much heavy rain in the middle, between the eye and the edge. There is less rain at the edge.

The eyewall is the rim of the eye. It has the stongest winds with very heavy rain, and a very dark sky. The rainbands are bands of heavy clouds which supply water for the abundant rain lasting for many days.