Hurricanes
What is a hurricane?
• A hurricane is a type of tropical cyclone,
the general term for all circulating weather
systems over tropical waters
• Hurricanes rotate counter clockwise in the
Northern Hemisphere and clockwise in the
southern hemisphere.
When Is Hurricane Season?
• June
through
November
st
31 .
st
1
Hurricane Facts:
Tropical storms need warm water(at
least 80 degrees) to grow
The warm water evaporates into the
storm, releasing the stored heat
energy when it condenses
The average hurricane uses as
much energy in a day as the entire
US in 6 months
More Hurricane Facts…
Hurricanes help maintain the heat
balance of the Earth
Hurricanes move with large
currents of air in the atmosphere.
The direction of the storm is not
altered by land masses.
Hurricanes can not be stopped
with nuclear weapons or cloud
seeding
What conditions must be present
for a hurricane to develop?
• Warm ocean
temperatures (>80˚ F)
up to 60m deep
• Little to no wind shear
• Low pressure system
at least 5˚ North or
South of Equator
• Rotation caused by
winds
Statistics
• Each year, on average, 10 tropical storms,
of which six become hurricanes, develop
over the Atlantic Ocean, Caribbean Sea,
or Gulf of Mexico.
• Many of these remain over the ocean;
however, about five hurricanes strike the
United States coastline every three years.
• Of these five, two will be major hurricanes,
category 3 or greater on the SaffirSimpson Hurricane Scale
Hurricane Anatomy
Comparison of Terms
• Tropical Disturbance
Group of thunderstorms in the tropics
that are present for at least 24 hours
• Tropical Wave
Lack of circulation, winds <25 mph and
every direction
• Tropical Depression
Closed circulation but disorganized,
winds at least 25 mph
Comparison of Terms
• Tropical Storm
Shower and thunderstorm moves over
closed circulation, winds greater than 39
mph
•
Hurricane
Eye is developed, winds > 74 mph
A Hurricane
• Maximum sustained winds of 74 mph (64
• knots) or higher.
• In the western Pacific, hurricanes are called
"typhoons," and similar storms in the
Indian Ocean are called “cyclones”
• In the Atlantic, they are called “hurricanes”.
Compare the following…
By what two factors is hurricane
strength measured?
Wind Speed
Barometric Pressure
What is the Scale Used to
Categorize Hurricanes?
Saffir-Simpson Scale
Category
Max Wind Speed
(mph)
Min. Surface
Pressure (mb)
Storm Surge m
(ft)
1
74-96
> 980
1-1.7 (3-5)
2
97-111
979-965
1.8-2.6 (6-8)
3
112-131
964-945
2.7-3.8 (9-12)
4
132-155
944-920
3.9-5.6 (13-18)
5
> 155
< 920
> 5.7 (>19)
Source: http://kids.earth.nasa.gov/archive/hurricane/saffir-simpson.html
How do Hurricanes
Destroy?
1. Wind
2. Rain
3. Storm Surge
4. Tornadoes
WIND
HEAVY
RAIN
AND
FLOODING
STORM SURGE
Southwest Florida
averaged about two
hurricanes per decade
through 1960, but only
near-misses since then!
Hurricane Season 2001
1961 to 1999 were hurricane free
The population of Southwest Florida is
more than 8 times what it was in 1960!
Most of the new people live within 10
miles of the coast or tidal water!
No one knows for sure what will happen
with the next storm, which may come
sooner than later, based on climate
studies!
Why no Hurricanes?
Luck
and the Atlantic Ocean
thermohaline
conveyor belt!
Higher salt levels in the North
Atlantic (1930s, 1940s & 1950s)
cause the Atlantic currents to
speed up, bringing more major
hurricanes to the US Coast!
Lower salt levels (1900-1925
and 1970-1994) cause the
current to slow down and fewer
major hurricanes impact the US
Coast!
The Atlantic thermohaline
conveyor belt circulation
is moving quickly once
again. This is likely the
beginning of a 2 to 3
decade long period of
increased hurricane
landfalls on the US
Coastline!
A LARGER RISK OF HURRICANES
+
MANY, MANY MORE PEOPLE
=
A BIGGER RISK THAN
EVER!
1930 - 2005
Costliest Storms in US History
2006 NOAA Hurricane Outlook
9 of the last 11 Hurricane Seasons have been have
been above normal
2006 NOAA Hurricane Outlook
13 - 16 Named Storms ( 11 is the normal average – 28 in 2005)
8 - 10 Hurricanes ( 6 is the normal average – 15 hurricanes in 2005)
4 - 6 Major Hurricanes (Cat 3 or greater with winds 111 mph or greater)
( 2 is the normal average – 7 major in 2005)
80% chance above normal, 15% chance near normal, 5% chance
below normal
NOAA’s 2006 Seasonal
Hurricane Outlooks
Atlantic
Outlook
Chance Above Normal
Chance Near Normal
Chance Below Normal
Tropical Storms
Hurricanes
Major Hurricanes
ACE % of Median
Categorical
Outlook
80%*
15%
5%
East Pacific
Outlook
Central Pacific
Outlook
5%
15%
80%
NA
13-16
12-16
8-10
6-8
4-6
1-3
135%-205% 45%-85%
Above
Normal
Below
Normal
2-3 tropical systems
(includes tropical
depressions)
Below
Normal
* 80% is highest probability ever issued in a May Outlook
14
Hurricane Floyd
Hurricane Floyd (1999) caused
massive flooding in North Carolina