1. CHAPTER 11
HURRICANES

2. ANATOMY OF A HURRICANE Hurricane Intense storm of tropical origin
Winds >64 knots (74mph)
Forms:
Warm Northern Atlantic
Eastern North Pacific Oceans

3. ANATOMY OF A HURRICANE
Eye
Eye Wall
Spiral Rain bands

4. ANATOMY OF A HURRICANE Eye: Calm As move into eye:
Air temperature: Increases
Wind speeds: Slow or Slacken
Rainfall: Ceases or Stops
Sky appearance: Sky brightens

5. ANATOMY OF A HURRICANE Eye Wall: Adjacent to the eye Thunderstorms
Whirl around the center and upward (15km or 49,000)

6. ANATOMY OF A HURRICANE Spiral Rain bands: Surface winds:
Increase in speed
Blow counterclockwise (Northern Hemisphere)
Inward toward its center

7. IMPORTANT POINTS Hurricanes form: Hurricane strength:
Over warm tropical waters
Light winds converge
Humidity is high in a deep layer
WINDS ALOFT ARE WEAK
Driving Force: latent heat
Hurricane strength:
Grow in strength
Decrease in strength

8. HURRICANE MOVEMENT Hurricanes mostly form over tropical oceans
EXCEPT: Southern Atlantic & Eastern South Pacific
North Pacific and North Atlantic
Steered by EASTERLY winds and move WEST

9. HURRICANE MOVEMENT

10. HURRICANE MOVEMENT Hurricane Path: Actual path:
Swing north around the subtropical high
Caught in the westerly flow
Actual path:
Determined: storm structure and interaction with the environment
Eastern North Pacific: normally westward away from the coast

11. HURRICANE MOVEMENT The Hawaiian Islands: Weaken before hits islands
Direct path of many eastern Pacific hurricanes and tropic storms
Weaken before hits islands

12. HURRICANE MOVEMENT Question:
Northward moving hurricane over the Atlantic survives longer than its counterpart at the same latitude over the Eastern Pacific
The surface water over the Atlantic is much warmer

13. HURRICANE PATH When on approach from the east:
Highest winds are usually on its north (poleward)
Winds propelling storm push added with winds on the north side and subtract from the winds on the south (equator) side.

14. DESTRUCTION AND DAMAGE
Gloria 9/27/1985
Moving northward but the net transport of water directed eastward toward the coast
Ekman Spiral and Coriolis
North wind caused a net transport of water toward the shore

15. DESTRUCTION AND DAMAGE
Swells
Large waves (10-15m or 33-49ft)
Move outward away from the storm
Damage
Wind
Waves
High Seas
Flooding

16. DESTRUCTION AND DAMAGE
Flooding (Most destructive)
Aided by the low pressure of the storm
Low pressure regions ocean level rise ½ meter
Storm Surge
High water + high winds and the net transport of water toward the coast
Storm Surge- abnormal rise of several meters in the ocean level, which engulfs low-lying areas

17. DESTRUCTION AND DAMAGE
Storm Surge
Before
During

18. DESTRUCTION AND WARNING
Other Damage
Tornadoes
~ ¼ US hurricanes tornadoes
Why?
Not quite known.
Surface topography may play a role by initiating the convergence and so the rising of surface air.

19. HURRICANE WARNING Hurricane Watch Hurricane Warning
Poses a direct threat to an area
24-48 hours before the storm arrives
National Hurricane Center (Florida)
Pacific Hurricane Center (Hawaii)
Hurricane Warning
Appears to strike an area within 24 hours

20. SAFFIR-SIMPSON SCALE Saffir-Simpson Scale “Tropical Depression”
“Tropical Storm” (given name)
Ranked from 1-5
Category 1- Lowest rank
Category 3- Major hurricane
Category 5- Severe damage

21. Damage mainly to trees, shrubbery, and unanchored mobile homes
SAFFIR-SIMPSON SCALE
Scale
Central Pressure
Winds
Storm Surge
Damage mb
in.
mi/hr
knots ft m 1
≥980
≥28.94
74-95
64-82
4-5
~1.5
Damage mainly to trees, shrubbery, and unanchored mobile homes 2
96-110
83-95
6-8 ~
Some trees blown down; major damage to exposed mobile homes, some damage to roofs of buildings 3
96-113
9-12 ~
Foliage removed from trees; large trees blown down; mobile homes destroyed; some structural damage to small buildings 4
13-18 ~
All signs blown down; extensive damage to roofs, windows, and doors; complete destruction of mobile homes; flooding inland as far as 10km (6mi); major damage to lower floors of structures near shore. 5
< 920
< 27.17
>155
>135
>18
>5.5
Severe damage to windows and doors, extensive damage to roofs of homes and industrial buildings; small buildings overturned and blown away; major damage to lower floors of all structures less than 4.5m (15ft) above sea level within 500m of shore.

22. NAMING HURRICANES Assigned “tropical storm” strength By 1953
Previous naming methods:
Latitudes and longitudes
Letters of the alphabet (WWII)
By 1953
Female names used using the alphabet

23. NAMING HURRICANES 1978 1979 Names retired
Eastern Pacific used both male and female
1979
North Atlantic began this alternating practice as well
Names retired

24. WRAP UP HURRICANES
Hurricanes are tropical cyclones with winds that exceed 64 knots (74mph)
Consists of a mass organized thunderstorms that spiral in toward the extreme low pressure of the storm’s eye
Storms are given a name at the Tropical Storm category
The energy source that drives hurricanes comes from primarily a release of latent heat

25. Wrap Up Hurricanes
In the Northern Hemisphere Hurricanes blow counterclockwise around the eye
In the eye the weather is calm, no rain, no wind, sunny
Eye wall: Intense rain, wind, and thunderstorm
Hurricanes develop in warm tropical waters
Hurricanes can spawn tornadoes
Weaken over cold water and land

26. Wrap Up Hurricanes Hurricane damage
Storm Surge, Wind, Flooding
Usually the most damage is caused by huge waves and flooding with the storm surge causes the most damage
Difference between hurricane and typhoon
Location:
western North Pacific areas- typhoon
Australia and India- cyclones

27. References: http://geology.com/hurricanes/named-hurricane-fran.gif