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 1st through November 31st.

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 Saffir-Simpson Hurricane Scale

Hurricane Anatomy

Comparison of Terms

• Tropical DisturbanceGroup 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 DepressionClosed 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 ScaleCategor

yMax 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. Rain3. Storm Surge4. Tornadoes

WINDWIND

HEAVYHEAVY

RAINRAIN

ANDAND

FLOODINFLOODINGG

STORM SURGESTORM SURGE

Southwest Florida Southwest Florida averaged about two averaged about two

hurricanes per hurricanes per decade through decade through

1960, but only near-1960, but only near-misses since then!misses since then!

Hurricane Season 2001

1961 to 1999 were hurricane freeThe 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?Why no Hurricanes?

LuckLuck

and the Atlantic and the Atlantic Ocean thermohaline Ocean thermohaline

conveyor belt!conveyor belt!

Higher salt levels in the North Higher salt levels in the North Atlantic (1930s, 1940s & 1950s) Atlantic (1930s, 1940s & 1950s) cause the Atlantic currents to cause the Atlantic currents to speed up, bringing more major speed up, bringing more major hurricanes to the US Coast!hurricanes to the US Coast!

Lower salt levels (1900-1925 Lower salt levels (1900-1925 and 1970-1994) cause the and 1970-1994) cause the current to slow down and fewer current to slow down and fewer major hurricanes impact the US major hurricanes impact the US Coast!Coast!

The Atlantic thermohaline The Atlantic thermohaline conveyor belt circulation conveyor belt circulation is moving quickly once is moving quickly once again. This is likely the again. This is likely the

beginning of a 2 to 3 beginning of a 2 to 3 decade long period of decade long period of increased hurricane increased hurricane landfalls on the US landfalls on the US

Coastline!Coastline!

A LARGER RISK OF A LARGER RISK OF HURRICANESHURRICANES

++

MANY, MANY MORE PEOPLEMANY, MANY MORE PEOPLE

==

A BIGGER RISK THAN A BIGGER RISK THAN EVER!EVER!

1930 - 2005

Costliest Storms in US History

2006 NOAA Hurricane Outlook9 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 East Pacific Central Pacific Outlook Outlook Outlook

Chance Above Normal 80%* 5%Chance Near Normal 15% 15% NAChance Below Normal 5% 80%

Tropical Storms 13-16 12-16 2-3 tropical systems Hurricanes 8-10 6-8 (includes tropical Major Hurricanes 4-6 1-3 depressions) ACE % of Median 135%-205% 45%-85%

Categorical Above Below BelowOutlook Normal Normal Normal

* 80% is highest probability ever issued in a May Outlook 14

Hurricane Floyd

Hurricane Floyd (1999) caused Hurricane Floyd (1999) caused massive flooding in North massive flooding in North

CarolinaCarolina

http://www.nasa.gov/mpg/126449main_katrina_fred_animation.mpg