1. Tropical Storms and Hurricanes

2. Super Hurricanes Motivation

3. This material was partially provided by the following sources: Prof
This material was partially provided by the following sources: Prof. Jennifer Collins (Florida State University), Aguado and Burt: Understanding Weather and Climate Comet educational program - UCAR (see websites in the last slide) Mr. Forest Cannon (graduate student Dept. Geography)

4. Tropical Cyclones and Hurricanes
Tropical cyclone and hurricane development, structure, and movement
Hurricane damages, warning systems, and naming conventions

5. They are all considered tropical cyclones
Regional Names
Extremely strong tropical storms go by a number of different names, depending on where they occur.
Over the Atlantic and eastern Pacific they are hurricanes.
Those over the extreme western Pacific are called typhoons; those over the Indian Ocean and Australia are cyclones.
They are all considered tropical cyclones

6. Hurricanes, Typhoons and tropical Cyclones around the globe.
Seasonal Variability and local names
Hurricanes
Typhoons
Cyclones
Hurricanes
Cyclones
Cyclones
Hurricanes, Typhoons and tropical Cyclones around the globe.

7. Some of the main characteristics of a Hurricane
Hurricanes have sustained wind speeds of 120 km/hr (74 mph)
and are typically about 600 kilometers (350 mi) wide.
Sea level pressure near the center of a typical hurricane
is around 950 mb, but pressures as low as 870 mb
have been observed for extremely powerful hurricanes.

8. Hurricanes obtain most of their energy from the
latent heat released by condensation and are most
common where a deep layer of warm water fuels them.
August and September are the prime hurricane months
in the Northern Hemisphere, while January to March
is the main season in the Southern Hemisphere.

10. Did you know…
Hurricane numbers vary considerable each year with a maximum number in the North Atlantic ever recorded in a single year of 15. This of course occurred recently in the infamous 2005 season. A minimum number of 2 occurred in 1982 which was an El Nino year. There is a mean number of hurricanes in this basin of just under 6 a year.

11. Important questions: Why do hurricanes form?
What causes their interannual variability? That is, why sometimes they are so frequent (as in 2005 – 15 hurricanes) and other times so rare (as in 1982 – 2 hurricanes – El Nino year)

12. Gray’s factors for tropical cyclone formation
Geographic
Coriolis Force sufficient to give initial cyclonic spin
Dynamic
Low vertical wind shear (shear is the vertical variation of the wind either in speed or direction)
Thermodynamic
High values of relative humidity
Sea Surface Temperatures > oC (~79-81oF) to a depth of 60 m (~200 ft)
An unstable atmosphere
To answer this one needs to refer to the pioneering work of Bill Gray whose seasonal tropical cyclone forecasts the news often quotes.
When considering the N Atlantic Ocean, Gray noted the factors necessary for tropical cyclone formation.
Coriolis force initiates the spin of the tropical cyclone. It occurs because we are on a rotating planet and causes a right deflection in the NH and a left deflection in the SH resulting in counter clockwise and clockwise flow of air in the NH and SH respectively.
A geographic factor (influenced by latitude)
Dynamic factors
Thermodynamic factors

13. Coriolis effect and hurricanes
Top view
Low
Low
No Coriolis Effects
With Coriolis Effects
(Northern Hemisphere example)

14. Internal Dynamics
Horizontal Pressure Gradient
Coriolis Force L

15. No tropical cyclones, hurricanes or Typhoons: blame Coriolis: 5S-5N
Negligible Coriolis Force near the Equator means there are no hurricanes there
No tropical cyclones, hurricanes or Typhoons: blame Coriolis: 5S-5N
The farther from the equator the greater the coriolis force, it is negligible along the equator. This is why hurricanes do not form on or within a few degrees of the equator.

16. 2nd Inhibiting factor: wind shear
Speed Shear
Direction
Shear
With high vertical windshear the storm gets ripped apart.
Directional wind shear is the change in wind direction with height. In the image (right), the view is looking north. The wind near the surface is blowing from the southeast to the northwest. Upper-level winds are blowing from the SW.
Speed shear is the change in wind speed with height. In the illustration the wind speed is increasing with height as air moves away from the frictional influences.
Strong vertical shear is the combination of directional shear and strong speed shear

17. The effect of Shear on the organization of the storm
Heat and moisture spread out over a larger area
Heat and moisture focused over a small area
More efficient in organizing tropical cyclones

18. Let’s look at December climatology of the zonal wind profile with height between 20S-30N and 100W-30W
Westerlies
Easterlies

19. Example of the mean zonal winds between 100W and 30 W during December El Nino 1997
Example of the mean zonal winds between 100W and 30 W during December La Nina1988
Westerlies
Westerlies
Easterlies
Easterlies

20. Example of the mean zonal winds between 100W and 30 W during December El Nino 1997
Example of the mean zonal winds between 100W and 30 W during December La Nina1988
Westerlies
weaker
Easterly anomalies
Westerlies
intensified
Easterlies weaker
Easterlies near normal
Increase in the vertical wind shear during El Nino years

21. High relative humidity required: one of the most important ingredients to form hurricanes is the release of latent heat to the atmosphere
Latent heat released due to condensation warms the atmosphere and cause the decrease of pressure at surface
There must also be high enough relative humidity for significant condensation to occur, providing latent heat.
Low pressure
As sea level pressure decreases, more air converges at the center of the storm, more latent heat is released and the storm becomes stronger and more powerful, with increasing winds

22. Warm water through depth required: water vapor is the fuel of tropical storms
Sea Surface 28 26
Temperature (°C)
Depth
High sea surface temperatures! This is key, and that’s why talk of global warming is so interesting for those interested in TC formation. According to Grey, the threshold for TC formation is 26C to a depth of at least 60 meters.
The high temperatures have to reach a certain depth because otherwise as the winds of a storm stir up the waters beneath it the cooler waters will rise to the surface and inhibit formation. 24

23. Cyclogenesis
NEGLIGIBLE CORIOLIS

24. Cyclogenesis: origin of cyclones
APPROXIMATE AREA OF WARM SST

25. Ocean Temperature IKE Deadly Hurricanes
IKE

26. Ocean Temperature
IKE

27. Where do Hurricanes originate
Hurricanes often originate as Tropical Disturbances
Tropical disturbances are disorganized groups of
thunderstorms having weak pressure gradients and
little or no rotation.
Most tropical disturbances that enter the western Atlantic
and become hurricanes originate in easterly waves, large undulations or ripples in the normal trade wind pattern.

28. The importance of monitoring wave activity over west Africa
Easterly waves have surface convergence and cloud cover
east of the axis and divergence to the west.

29. Tropical Weather & Waves
Tropical winds typically blow from the east, and when they encounter a slow moving trough of low pressure, called a tropical wave, the winds initially converge and lift to produce showers and thunderstorms.

30. Pre-Existing Disturbance
BILL
FRED
For a tropical cyclone to form, a disturbance must already be present. The convergence at this low pressure system is what initiates the cyclonic development.

31. ORIGIN OF CYCLOGENESIS
Wind Shear
WESTERLIES
EASTERLIES
IDEAL FOR CYCLONES
ORIGIN OF CYCLOGENESIS
DOLDRUMS
NCEP Reanalysis and TC data for composites:

32. When a tropical disturbance develops to the point that
there is at least one closed isobar on a weather map,
the disturbance is classified as a tropical depression.
If the depression intensifies further and maintains wind
speeds above 60 km/hr, it becomes a tropical storm.
A further increase in sustained wind speeds
to 120 km/hr creates a true hurricane.
PHASES OF DEVELOPMENT

33. Hurricane Lifecycle

34. A cross section of a typical hurricane.

35. Internal Dynamics

36. The hurricane eye is a region of relatively clear skies,
slowly descending air, and light winds.
Along the margin of the eye lies the eye wall,
the zone of most intense storm activity with
the strongest winds, thickest cloud cover, and
most intense precipitation of the entire hurricane.

37. Structure of a Hurricane
In this image of Hurricane Elena, the central area of broken clouds is the eye, surrounded by an eye wall cloud and spiral rain bands, with a total diameter nearing 500 kilometers.

38. http://www. nasa. gov/mission_pages/station/multimedia/hurr_ike091008
Hurricane Ike (September 10/2008): downlinked by the crew of the International Space Station, flying 220 statute miles above Earth. The center of the hurricane was near 23.8 degrees north latitude and 85.3 degrees west longitude, moving 300 degrees at 7 nautical miles per hour. The sustained winds were 80 nautical miles per hour with gusts to 100 nautical miles per hour and forecast to intensify. Photo Credit: NASA

39. IKE, September 9/2008

40. Cross-section of a hurricane showing cloud patterns and air flows (a), rainfall intensities (b), pressure distributions (c), and wind speed (d).

41. Hot towers (above) are embedded in some eye walls and last between 30 minutes and 2 hours. Hot towers are localized portions of eye walls that rise to greater heights (up to 12 km, or 7 mi) than the rest of the eye
wall and may indicate that the hurricane will intensify within 6 hours.

42. A hypothetical hurricane moves northward at 50 km/hr. Along the
right-hand side, the 200 km/hr winds are in the same direction as the
movement of the storm, so there is a net-wind speed of 250 km/hr.
On the left side, the net winds are southward at 150 km/hr.

43. Hurricanes and tropical storms have a tendency to move north or
northeast out of the tropics along the southeast coast of North America
and often move in wildly erratic ways. After making landfall,
a tropical storm may die out completely within a few days.

44. Sources of destruction from a hurricane
Winds
Flooding
Rain
Storm Surge
Waves
Tornado
Down-drafts

45. Effects of Tropical Cyclones
Wind and Rain
Storm Surge
Hurricanes are among nature’s most destructive events and annually account for unparalleled environmental destruction and loss of life.

46. Precipitation
Tropical Cyclones account for a large percentage of Annual precipitation in many regions
Single events can be extremely destructive especially in mountainous regions
Create Flooding and Landslides
Influenced by geography

47. Storm Surge
Created by barometric low in hurricane center as well as wind driven piling up of water
Elevated sea level follows storm
For every milibar of pressure decrease, the water level rises 1 cm.
When cyclone makes landfall water surges inland
When associated with high tide can be up to 25 feet
Most destructive part of tropical cyclones
Flooding can last for extended periods of time destroying local infrastructure (New Orleans, Bangladesh)

49. More on the hurricanes Revision of concepts: (second movie)
Movie showing storm surges and impacts on coastal areas

50. Comparison of hurricanes and mid-latitude cyclones
Similarities:
Type of low pressure system
Wind direction
Differences:
Energy derivation
Strongest winds
Surface charts

51. Can you tell if they are tropical or extratropical cyclones?

52. Locations of hurricane landfalls from 1950 through 2004.

53. When forecasters predict that an approaching hurricane
will reach land in more than 24 hours, they issue a
hurricane watch. If it is expected to make landfall
over the United States within 24 hours,
they issue a hurricane warning.
NOAA Official link for hurricane watch

54. Hurricane Watch & Warning
The National Hurricane Center in Florida issues a hurricane watch 24 to 48 hours before a threatening storm arrives, and if it appears that the storm will strike within 24 hours, a hurricane warning is issued.
While some consider the warning area too large, causing unneeded evacuation, such evacuations have saved many lives.
Hurricane Hugo, with peak winds near 174 knots, caused tremendous damage.

55. The Saffir-Simpson scale classifies hurricanes into five categories,
with increasing numbers corresponding to lower central pressures,
greater wind speeds, and larger storm surges.

56. Hurricane Names and Cost
Category 5 Hurricane Andrew (1992) was the costliest US storm (prior to 2005 season!), but it ranks as less intense than 1935 and 1969 hurricanes.
Hurricane names are chosen from an alphabetical list of male and female names for the Atlantic and Pacific, some of which are retired if the storm was especially damaging.

57. Tropical Cyclones names for the Atlantic sector
2009
2010
2011
2012
2013
2014
Ana Bill Claudette Danny Erika Fred Grace Henri Ida Joaquin Kate Larry Mindy Nicholas Odette Peter Rose Sam Teresa Victor Wanda
Alex Bonnie Colin Danielle Earl Fiona Gaston Hermine Igor Julia Karl Lisa Matthew Nicole Otto Paula Richard Shary Tomas Virginie Walter
Arlene Bret Cindy Don Emily Franklin Gert Harvey Irene Jose Katia Lee Maria Nate Ophelia Philippe Rina Sean Tammy Vince Whitney
Alberto Beryl Chris Debby Ernesto Florence Gordon Helene Isaac Joyce Kirk Leslie Michael Nadine Oscar Patty Rafael Sandy Tony Valerie William
Andrea Barry Chantal Dorian Erin Fernand Gabrielle Humberto Ingrid Jerry Karen Lorenzo Melissa Nestor Olga Pablo Rebekah Sebastien Tanya Van Wendy
Arthur Bertha Cristobal Dolly Edouard Fay Gonzalo Hanna Isaias Josephine Kyle Laura Marco Nana Omar Paulette Rene Sally Teddy Vicky Wilfred

58. Hurricane Andrew In video, they added stuff about Andrew.
Andrew happened whilst film was being produced.
Andrew moved thru Homested, South of Miami
Often a double wammy happens as a hurricane hits land, goes over gulf and hits another place.
Camile CAT 5: 1969
Gilbert didn’t get much press as it didn’t kill many people
Andrew
Katrina: will go down in the record as most devastating storm
Rita did damage but in a couple of years from now, she will be forgotten.
Figure 5.41

59. Hurricane Andrew Devastation in Homestead, Florida August 24, 1992

60. Rita 9/23/05 Katrina 8/28/05 Wilma 10/21/05
Emily
7/21/05
The number of Atlantic tropical storms (purple), hurricanes (orange), and Category 3–5 hurricanes (green) by year, 1851–2004.

61. What was the deadliest hurricane in the USA history?

62. At the turn of the last century Galveston, Texas was a sophisticated seaport of 38,000 people, a city prosperous from the cotton trade and richer in millionaires than even Newport, R.I. It was the first city in Texas with phones and electricity, and its residents enjoyed a grand lifestyle: an opera house, 50 miles of streetcar track and foreign consulates for 19 countries. On Friday evening, Sept. 7, 1900, many of the residents of Galveston were settling down to dinner, few if any of them concerned about the steady 15 mph northerly wind rattling their windows. Within 48 hours, at least 8,000 of the townspeople --almost one in five Galvestonians -- would be dead, victims of the single worst natural disaster in U.S. history. The tragedy killed more Americans than the legendary Johnstown Flood, the San Francisco Earthquake, the 1938 New England Hurricane and the Great Chicago Fire combined.

63. The 15 deadliest Atlantic Hurricanes in history : 1742-2009
Rank:
Name / Areas of Largest Loss:
Dates:
Deaths: 1.
"Great Hurricane" Martinique, Barbados, St. Eustatius
10-16 Oct 1780
22000 2.
Great Galveston Hurricane
8 Sep 1900 3.
Mitch: Honduras, Nicaragua
10/ /5 1998
9086 4.
Fifi: Honduras
14-19 Sep 1974 5.
Dominican Republic
1-6 Sep 1930
8000 6.
Flora: Haiti, Cuba
9/30-10/8 1963 7.
Pointe-a-Pitre Bay, Guatemala
6 Sep 1776
6000 8.
Newfoundland Banks
9-12 Sep 1775
4000 9.
Puerto Rico, Carolinas
8-19 Aug 1899
3433
10.
FL, PR, Martinique, Guadeloupe, Turks
12-17 Sep 1928
3411
11.
Cuba, Cayman Islands, Jamaica
4-10 Nov 1932
3107
12.
Jeanne: Haiti, Dominican Republic, Bahamas, Florida
13-29 Sep 2004
3000
13.
Central Atlantic
16-17 Sep 1782
14.
Martinique
Aug 1813
15.
El Salvador, Honduras
4-8 Jun 1934

64. *Very interesting material for consultation: (comet/ucar website)
Video of Tropical Cyclone Ingrid (2005) making landfall in Australia:
Hurricane intensity scale:
Access comet website
Pass: victory

65. Work in groups: Summarize what you have learned regarding:
1) tropical cyclones names
2) tropical cyclones formation, development, propagation
3) Characteristics (rain, winds, pressure)
4) Inhibiting factors
5) Damages
6) Warning and watch
7) Role of El Nino/La Nina phenomenon for the frequency of hurricanes

66. Interpret the information provided in the next slide