Global atmospheric circulation

Location of cyclonic storms

Due to Coriolis forces, cyclonic storms must form at least 300 mi from the Equator (about 5 degrees N or S)

Traits common to tropical cyclones Form between latitudes of 5° and 20° N

or S Most common in summer months of

respective hemisphere Form in E or SW Pacific, E N Atlantic

Ocean, and N Indian Ocean Rotational winds produce low pressure Warm water of 25 - 26° C [77-80° F]

Extratropical cyclones Form over land or water in higher

latitudes, usually 30 - 70 ° latitude Cool central cores driven by jet stream

Circulation pattern around eye

Eye wall

North Atlantic storm tracks

Definitions of Tropical, Low-Pressure Weather Systems. Storms begin as Disturbances and can Become

Hurricanes Tropical disturbance

Organized mass of convectional air and thunderstorms with partial rotation present; generally 100 to 300 nautical miles in diameter that originate in the subtropics or tropics

Tropical depression Closed circulation with sustained winds of 38 mph (33 kt

or 62 kph) or less Tropical storm – NAME ASSIGNED NOW

Sustained winds (1-minute measurement, 10 m above water) of 39 mph (63 kph or 34 kts) up to 73 mph (63 kts)

Hurricane Sustained winds of 74 mph (119 kph or 64 kts) or more

Naming of storms Done when tropical storm forms (winds

> 39 mph) Helps keep track of storm Six lists are used which repeat in 6 yrs Men’s names added in 1979 and

alternate with women’s names each year

This year–Alberto, Beryl, Chris, Debby, Ernesto…

Names retired for major storms Hugo, Carla, Floyd, Katrina, Rita, Sandy,

Wilma 77 retired since 1954, 28 since year 2000!

For United States, between 1851 and 2004, tropical storm occurrence rate

On average 8.5 storms per year 5.2 hurricanes 1.8 hurricanes hit land in U.S.

Worst months September, August, October

NOAA Predictions for 2013 season Jun 1 – Nov 30)

13 to 20 named storms 7 to 11 become hurricanes (>74 mph

winds) 3 to 6 will be major hurricanes (111 mph

or greater – Category 3)William Gray (Colorado State University) predicts 18 named storms 9 make hurricane status (>74 mph

winds) 4 major hurricanes (Category 3 or

higher)

Thermal energy drives cyclone Rotational forces extract more water

and heat from ocean surface Unstable conditions aloft Concentration of energy toward

center Spinning ice skater effect Conditions worsen

In northern hemisphere Storms curve to right Prevailing trade winds, Bermuda High

and Coriolis forces affect storm tracks

Two jet streams33,000 ft altStronger110 mph winter55 mph summer

43,000 ft altweaker

Cape Verde source area

Year 2005 was the worst in terms of number of named storms 21 formed, all names were used, so

Greek letters were assigned to the last six

Letter not used for names Q, U, X, Y, Z

Comparative activity2005 hurricane activity

2006 hurricane activity

Comparative activity2008 hurricane activity

2010 hurricane activity

Hurricane season for 2012

Hurricane Sandy changes

Oct 25, 2012 Oct 28, 2012

Hurricane Sandy facts Worst North Atlantic storm in 2012; second most costly in US

history ($50 billion; 285 died in seven countries)

Category 3 when it hit Cuba; intensity changed but was Cat 2 when offshore of US

Largest Atlantic storm (1,100 miles in diameter) Called “Superstorm” due to its severity and widespread damage;

merged with Arctic cold front Hit coast of New Jersey on Oct 29th, relatively late in the season Warm sea surface temperatures off East Coast (about 5 deg F

above normal) High pressure cell off Greenland stopped its normal eastward

motion Massive flooding in New Jersey and New York city.

Effects of cyclonic storms Storm surge

Wind-pushed waves; fetch in NE quadrant Lower pressure raises water level Effects amplified in bays and lagoons; seiches Worst at high tide Record surge 42 ft in Australia!

Flooding Greatest killer; often freshwater (rainfall

flooding) Avg hurricane produces rainfall equal to the

flow of the St. Lawrence River in THREE SECONDS!

Heavy rain Average storm produces about one trillion

gallons of rainwater daily, 3x annual usage in U.S.

T. S. Allison in 2001 dumped 37 in rain on Houston

Hilly topography affects rainfall; H. Agnes 1972 in Appalachian Mtns of eastern United States

High winds Direct damage Storm surge

Hatteras Island, NC, breached by Hurricane Isabel Sept 2003

Beach erosion in H. Dennis, 9/1/99

NC Outer Banks

Categories of Cyclones Wind damage

Category 1: 74 – 95 mph Category 2: 96 –110 mph Category 3: 111 – 130 mph Category 4: 131 – 155 mph Category 5: > 155 mph

Highest recorded winds – 190 mph Eyewall has highest velocity; landfall

location important

Wind velocities within a hurricane

Typical storm track off east coast of U. S.

H. Andrew, Aug 23-25,1992

Damage from Hurricane Andrew 1992

Risk factor for United States

Insurance Flood insurance $300 per year Wind and hail damage - $2,100 per year

Additional add on to cover roof damage Both required by bank for lending Deductible is 10 per cent of home value, so for a

$300,000 home it is $30,000; amount goes to 15% if the storm has a name

If a dead tree fall into your property, the owner of

the tree is liable; if it is a live tree, you pay! Ha!

Major hurricane hazard map

Highest

Second highest

Most costly storms in U.S.Rank Hurricane Year Category Damage

1 Katrina (LA,MS,AL) 2005 3 81,000,000,000

2 Andrew (SE FL, SE LA) 1992 5 26,500,000,000

3 Wilma (S FL) 2005 3 20,600,000,000

4 Charley (SW FL) 2004 4 15,000,000,000

5 Ivan (AL/NW FL) 2004 3 14,200,000,000

6 Rita (SW LA, N TX ) 2005 3 11,300,000,000

7 Frances (FL) 2004 2 8,900,000,000

8 Hugo (SC) 1989 4 7,000,000,000

9 Jeanne (FL) 2004 3 6,900,000,000

10 Allison (N TX) 2001 TS 5,000,000,000

11 Floyd (Mid-Atlantic & NE ) 1999 2 4,500,000,000

12 Isabel (Mid-Atlantic) 2003 2 3,370,000,000

13 Fran (NC) 1996 3 3,200,000,000

14 Opal (NW FL, AL) 1995 3 3,000,000,000

15 Frederic (AL, MS) 1979 3 2,300,000,000

Sandy $50 billion2012