Weather conditions associated with Caribbean systems

FOCUS QUESTION

What are the weather conditions associated with (tropical waves and hurricanes) Caribbean weather systems and formation?

TROPICAL WAVES

Are troughs of low pressure which occur in tropical areas.

Are often seen as inverted troughs of low pressure. A trough is an elongated area of low pressure, usually not associated with a closed circulation.

Disturbances in the tropical easterlies that typically move from east to west.

Across the tropics, causing areas of cloudiness and thunderstorm.

Feature convection typically on the east side (originate from eastern Africa).

Feature convection highly controlled by atmospheric moisture, upper-level features, topography, etc. Are significant rain producers.

Develop into tropical cyclones. To the west of a tropical wave:

Air is descending.

Weather is fair.

Wind blows from the north-east. Atmosphere becomes unstable as the trough passes over an area and there are strong updraughts (rising currents of air). Cumulonimbus clouds form: Resulting in heavy rain and thunderstorms. To the east of the wave:

Wind blows from the south-east. Tropical waves are common from April to November. HURRICANE

A hurricane is a type of storm called a tropical cyclone, which forms over tropical or subtropical waters. It is also a low-pressure system that generally forms in the tropics. Tropical cyclones are classified as:

Tropical depression

Tropical storm

Hurricane is an intense tropical weather system of strong thunderstorms with a well-defined surface circulation and maximum sustained winds of 74mph (64kt) or higher.

Hurricanes originate in the Atlantic Basin, which includes the Atlantic Ocean, Caribbean Sea, Gulf of Mexico, the eastern North Pacific Ocean and, less frequently, the central North Pacific Ocean.

PARTS OF A HURRICANE

Eye: The eye is the ‘hole’ at the centre of the storm. Winds are light in this area. Skies are partly cloudy and sometimes even clear.

Eye wall: The eye wall is a ring of thunderstorms. These storms swirl around the eye. The wall is where winds are strongest and rain is heaviest.

Rainbands: Bands of clouds and rain go far out from a hurricane’s eye wall. These bands stretch for hundreds of miles. They contain thunderstorms and sometimes tornadoes. HOW DO HURRICANES FORM? They only form over really warm ocean water of 80°F or warmer. (This is why it is common in the tropics, where temperatures are high all year round). Hurricanes also need wind action to form.

The thunderstorms with rains begin to move slowly with mild western winds (too much wind will disperse the build-up).

In a day or two, stronger vertical currents build up over the ocean surface upwards.

More warm air rises and the winds begin to move in circular manner, caused by Earth’s rotation.

The rising warm air causes pressure to decrease at higher altitudes.

The entire system is now in circular motion around a central point.

This is called a tropical depression, and it has wind speeds going up to about 38 miles per hour.

In a couple of days, as the system moves over warmer waters, the clouds expand even more and the winds begin to speed up.

Gale-force winds, thunderstorms and heavy rains are in full force at this point. This may be called a tropical storm and have wind speeds of up to 74 miles per hour.

Continuing its movement westwards, the tropical storm may be moving over even warmer waters.

The energy from the warm ocean, in the form of very warm air rising, and the gushing of cooler air replacing it, throws the entire storm into a fury of powerful, huge and monstrous spiral storms that can be seen from space.

The spiral has a calm centre, called the eye. The eye is surrounded by a towering and extremely dangerous vertical movement of thunderstorms.

This is called the eye wall.

The winds of the eye wall are so powerful that it spins and carries huge amounts of ocean water as it moves ashore.

The hurricane now makes landfall (has reached land).

With winds over 74mph to about 160mph, massive destruction is usually inevitable.

As the system is no more over water, its fuel has run out and begins to ease out.

The winds will subside and eventually end, but the rains may continue.