Hurricane Development

By Tom R. & Rachel L.
Hurricanes go through many different stages. All hurricanes start off as a tropical depression and then while they strengthen some will become tropical storms. If the storm strengthens further, then it will become a hurricane. If the storm hits the hurricane status, there are 5 categories that can rate the intensity of the storm.

Tropical Depressions

  • A typical tropical depression contains wind speeds of 23-39 mph.
  • Little organization
  • No real "cyclonic" motion
  • Made when thunderstorms come togeather
  • From satellite appears as though it is just a large thunderstorm.

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As one can see it looks just like a bunch of thunderstorms not a hurricane in any way.

Tropical Storms

  • A tropical depression contains winds of 39-73 mph
  • Usually move westward at about 10-20 kmph
  • Can cause damage, mainly in the way of heavy rainfall
  • Also known as tropical cyclones and typhoons
  • Weaken over land
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  • A storm that has evolved so that the wind speeds are over 73mph
  • Happens when surface pressure drops
  • Very clear rotation around center of hurricane
  • Earths strongest tropical cyclones
  • Centered around the eye of the hurricane
  • Rated acording to their wind speed
  • Scale ranges from 1-5 (5 being the strongest hurricane and 1 being the lowest hurricane)

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Category 1

  • 74-95 mph winds
  • Storm surge generally 4-5 feet above normal
  • Main damage done to bushes and unanchored mobile homes--no real damage to other structures
  • Minor pier damage
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This is an image of Hurricane Lili which occured in 2002. As one can see this hurricane has distinguished circular motion but has not developed a clear eye to rotate around yet.

Category 2

  • Winds of 96- 100 mph
  • Storm surge 6-8 feet above average
  • Noticeable damage to shrubs and trees, serious damage on some road signs, and minor damage to roofing
  • Marinas flood
  • Evacuation of some coastal residences and close islands required
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Compared to the image of Hurricane Lili, this picture of Hurricane Isabel in 2003 shows that the hurricane is developing more of an eye and is gradually becoming a more organized storm.

Category 3

  • Winds of 111-130 mph-- serious damage to trees and signs, and some damage to roofing, windows, and doors
  • Storm surge 12 feet above normal
  • Major flooding at coast and destruction of small structures near coasts
  • Major erosion of beaches
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As you can see, the eye of this storm is gradually getting more refined than the category 2 hurricane's eye.

Category 4

  • Winds of 131-155 mph
  • All shrubs, trees, and signs down
  • Extreme damage to roofing, windows, and doors.
  • Roofs collapse
  • Storm surge 13-18 feet above normal
  • Flat ground at most 10 feet above sea level flood as far as 6 miles inland
  • The eye is defined
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Not only is the hurricanes eye getting more refined, but the outer walls of the hurricane is getting more organized while it becomes a more powerful storm

Category 5

  • Winds more than 155 mph
  • serious damage to roofs
  • All signs down and most trees down
  • Storm surge higher than normal by 18 feet
  • Major damage to structures less than 15 feet above sea level within 500 yards of the coastline
  • Massive evacuation of areas low to the ground within 10 miles of
  • The eye is clearly defined
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Compared to the category 4 hurricane, one can see that this hurricane's eye is much larger and the outer walls of this hurricane are much more organized than the category 4 hurricane.

Factors in Hurricane Development

  • Warm ocean temperatures are a fuel sorce for hurricanes when above 80 degrees Fahrenheit
  • Easterly wind flow support the hurricane. Westerly winds help make sure that there is no shearing, which means tearing thunderstorms.
  • Rotation. Without rotation, the wave is only an area of low pressure.
  • All of these factors are necessary for the storm or hurricane to stay strong