Geog Unit 3 Lecture 2

A tropical system refers to

a tropical cyclonic storm of a warm-core low pressure cell, inward spiraling rainbands, and having sustained winds of more than 73 mph.

For formation, hurricanes

begin life only in warm tropical waters.

Average diameter of hurricanes

~360 miles

Hurricanes exhibit a

strong pressure gradient, generating strong winds, which develops around the center of circulation (the eye) with the strongest winds in the eye wall.

Hurricane systems require

warm, moist air which yields great instability and lift. this is the system fuel source.

Hurricanes must form over warm ocean waters with temperatures

greater than 27 degrees Celsius (81 degrees F)

The Hurricane eye is the

center of low pressure, usually with calm winds, clear skies, and weak downdrafts.

The eye wall is the area

surrounding the systems eye and which exhibits the strongest pressure gradient, leading to intense winds.

The eye wall is typically the section that

causes the most damage.

Some hurricanes may develop double eye walls,

indicating that eye wall replacement is occurring.

Spiral rainbands are typically the

largest part of the storm in terms of areal coverage and consisting primarily of stratus and nimbostratus clouds, with light to moderate rain but embedded thunderstorms are often found within these bands.

Tropical disturbance is the term given to the

initial, disorganized mass of thunderstorms showing a weak pressure gradient and little, if any, cyclonic circulation.

Hurricanes are often in association with

an easterly wave, a large undulation or ripple in the normal trade wind pattern.

Tropical depression is the term given to a

tropical system which shows stronger cyclonic circulation around a weal low pressure center, greater development of the cloud mass.

A tropical depression has sustained winds near the center of the system between

25-38mph, and at this stage, it is assigned a number.

Tropical storm is the term given to a tropical system with a

well-developed cyclonic circulation around a strengthening low-pressure center, the beginnings of an eye wall and spiral rainbands, but usually no visibly distinct eye.

A tropical storm has sustained winds within the eye wall of between

39-73 mph. At this stage, the system is given a name.

A hurricane is a fully

developed tropical system with a strong cyclonic circulation, a visibly distinct center or “Eye”, a strong eye wall and well-organized spiral rainbands.

A hurricane has sustained winds within the eye wall more than

73 mph.

Winds are often on the

right half of the system, tornadoes are also more common in the upper-right quadrant.

Tropical systems have an average life span of

7-10 days but may last over 2 weeks.

Storm surge is the

abnormal rise of sea level and high waves along the coast because of the strong winds and low pressure associated with the hurricane.

The storm surge is most severe on the

right side of the storm as it makes landfall (in the Northern Hemisphere) because the winds here are blowing onshore thus pushing even more water against the coastline.

Storm surge, flooding, and wind damage are usually

the most severe on the right side, especially the upper-right quadrant, of the system.

Tropical Cyclone Seasons - Atlantic Ocean:

June 01 - November 30th with th peak month being September

A hurricane watch indicates that

hurricane winds (>73mph) from an approaching storm are possible within the specified arrea within 48 hours.

A hurricane warning indicates that

hurricane force winds from an approaching storm are expected within the specified area within 36 hours.