Transcript North Atlantic Hurricanes

North Atlantic Hurricanes
Presented By:
Jess Downing
Karen A. Kosiba
Hurricanes are:
• Tropical cyclones.
• Two-Celled Vortices
(contain both upward
and downward
motions).
• Cyclonic in the lower
levels and anticyclonic
in the upper levels.
• Atlantic Hurricane
Season: JuneNovember
Classification
• Tropical Cyclone: A tropical cyclone is the
generic term for a non-frontal synoptic scale lowpressure system over tropical or sub-tropical
waters with organized convection (i.e.
thunderstorm activity) and definite cyclonic
surface wind circulation.
• Tropical Depression: TC with winds near the
surface of less than 39 mph.
• Tropical Storm: TC with winds 39 to 74 mph.
• Hurricane: TC with winds of 74mph or greater.
http://www.aoml.noaa.gov/hrd/tcfaq/t
cfaqA.html#A2
Saffir-Simpson Hurricane
Damage Potential Scale
Naming a Storm
• Alphabetical, alternating female/male
• Names of minor hurricanes are reused on a
6 yr. cycle.
• The NHC retires a storm’s name if it
incurred heavy losses of life or extensive
property damage.
– Ex: Hugo (89), Andrew (92)
Hurricane Structure
• Eye
• Eye Wall
• Rain bands (Feeder bands)
Eye
• Generally free of tall
clouds.
• Winds are light.
• Air aloft is warm and
dry.
• Surface air pressures
are lowest due to
sinking and warming
of air.
• Diameter = 16-70 km
Book: Hurricanes of the North
Atlantic
Eye Wall
• Ring of cumulonimbus
clouds immediately
surrounding the eye.
• Contains strongest
winds and heaviest
rains.
• Contains (the majority
of) intense rising
motions.
Hurricanes of the North Atlantic
Spiral Feeder Bands
• Appearance (from
space) similar to a
spiral galaxy.
• Heavy rains and
squalls (strong winds
of short duration with
sudden
onset/dissipation).
• Outermost bands can
be 1000 km from
hurricane center.
Hurricanes of the North Atlantic
An Approaching Hurricane
• With the arrival of the first spiral rain
band—hard brief rain and sudden wind
gusts.
• Followed by partial clearing until the next
rain band arrives and squally weather
returns.
• As the center of the hurricane approaches,
frequency and intensity of the squall
increases.
Approaching Hurricane Cont.
• As the eye passes, winds become light
before switching direction and gaining
strength.
• The largest winds occur in the right side of
the vortex—the vector sum of the wind
velocity and the storm velocity.
How Does a Hurricane Work??
• Hurricanes are heat engines.
• Energy is provided by evaporation of warm
water from oceans.
• Water vapor carried up in cumulonimbus
towers.
• Rising air cooled by expansion leading to
condensation.
Hurricanes of the North Atlantic
Hurricanes Cont.
• Condensation releases energy which maintains
storm circulation.
• This release of latent heat reduces the rate of
adiabatic cooling (below that of dry air) thus
providing a constant upward force on the air
parcels.
• As long as the upper level outflow is greater than
the lower level inflow—the pressure will drop and
the storm will intensify.
Hurricanes of the North Atlantic
Favorable Environmental Conditions for
Hurricane Development
• SSTs of at least 26.5°C [80°F] throughout a depth of 50 m [150
ft]. Warm waters are necessary to fuel the heat engine of the
tropical cyclone.
• An atmosphere which cools fast enough with height such that it is
potentially unstable to moist convection.
• Relatively moist layers near the mid-troposphere 5 km [3 mi].
• A minimum distance of at least 500 km [300 mi] from the
equator—Need the Coriolis Effect!
• A pre-existing near-surface disturbance with sufficient vorticity
and convergence.
• Low values (less than about 10 m/s [20 kts 23 mph]) of vertical
wind shear between the surface and the upper troposphere.
Vertical wind shear is the magnitude of wind change with height.
http://www.aoml.noaa.gov/hrd/tcfaq/t
cfaqA.html#A10
Hurricane Fran,
hurricanetrack.com/1996.html
Hurricane Movement
• Hurricanes move with the air flow in which they
are embedded.
• Weaker storms are steered by low level winds.
Strongest storms are moved by upper level winds.
• Hurricanes of low latitudes track to the west—
Pushed by NE trade winds.
• Hurricanes of higher latitudes track more NW
steered by the anticyclonic flow around
subtropical high pressure system.
1999 Hurricane Season
www.botany.hawaii.edu/faculty/
cm_smith/Dictyota.htm
Hurricane Damage
•
•
•
•
Storm Surge
Inland Flooding
Wind Damage
Tornadoes
• What is it?
Storm Surge
– Domes of water produced by the action of
cyclonic winds during a hurricane, in which the
sea level can be up to five meters higher than
normal (Camille had a storm surge of 7m!)
– Waves on top of the surge are especially
damaging during high tide
• Causes 90% of deaths (drowning)
• Residents in low lying areas at greatest risk
• Water can be pushed into bays and rivers
(flooding)
• Erosion
• Sea water weighs 64 lbs per cubic foot!
Storm Surge Possibilities
www.swfrpc.org/hurr.htm
http://www.bahamasnet.com/images/r
oad1.jpg
Inland Flooding
• Usually brought on by heavy, storm-induced
rains that quickly swell rivers and streams
• These flooding rains are most dangerous for
people living inland
– Hurricane Camille (69) killed 109 people in VA
after making landfall in LA
Wind Damage
• Ability to be most
destructive to property
• Wind driven flying
debris
• Erosion
www.ci.hilton-head-island.sc.us/
Hurricane/family.html
Tornadoes
• Cause most damage in local areas far
removed from coastal regions.
• Approximately one-fourth of landfall
hurricanes produce tornadoes.
• Tornadoes produced are usually F2 or
below.
• Tend to form in the front right quadrant of
the hurricane—vertical wind shear is
greatest.
Saffir/Simpson Scale
and Property Damage
• Cat 1: No damage to building structures. Minor
damage to mobile homes, shrubbery, and trees.
Some coastal road flooding and minor pier
damage. Some roof, door, and window damage on
buildings.
• Cat 2: Considerable damage to vegetation, mobile
homes, and piers. Coastal and low-lying escape
routes flood 2-4 hours before arrival of eye wall.
Small craft in open anchorage break moorings.
Some structural damage to small residences.
Hurricanes of the North Atlantic
Property Damage Con’t
• Cat 3: Mobile homes are destroyed. Flooding near
the coast destroys smaller structures with larger
structures damaged by floating debris. Terrain
lower than 5 ft ASL may be flooded inland 8 mi or
more. More extensive wall failure with some
complete roof structure failure on small
residences.
• Cat 4: Major erosion of beach. Major damage to
lower floors of structures near shore. Terrain lower
than 10 ft ASL may be flooded, requiring
evacuation of residential areas inland to 6 miles.
Complete roof failure on many homes and
industrial buildings.
Hurricanes of the North Atlantic
Property Damage Con’t
• Cat 5: Some complete building failures with small
buildings blown over or away. Major damage to
lower floors of all structures located less than 15 ft
ASL and within 500 yd of the shoreline.
Evacuation of areas on low ground within 5 to 10
mi of shore may be required.
Hurricanes of the North Atlantic
According to FEMA, Hurricane Georges cost them
$2.5 billion alone. (http://www.fema.gov/library/df_7.htm)
www.fema.gov/library/
Hurricane Warnings
• Coastal communities are divided up into
zones according to their susceptibility to
damage (in order of severity):
– 1. Barrier islands and beaches.
– 2. Mainland surge areas exposed to over-wash
flooding from the storm surge.
– 3. Areas far enough inland to avoid the surge.
Hurricane Warnings Con’t
• Coastal hurricane warnings are usually issued 18
to 24 hours prior to expected arrival of the
hurricane.
• This time interval is an optimized trade off
between the desire to provide maximum warning
lead time and the ability to keep the size of the
warning area within reasonable limits.
• Lead times are determined by how long it is
expected to take to get people out of harm’s way.
Societal Vulnerability to
Hurricanes
• Dramatic rises in coastal populations
– More people = higher property values
– Approx 45 million live on coast (TX to ME)
• More vacationers to coasts
– Usually to the barrier islands or immediate
shoreline
• Problems with evacuating the crowded
areas
– FL keys can require up to 36 hrs to evacuate
Hurricane Deaths Have Decreased—
Property Losses Have Increased
www.usgcrp.gov/.../
overviewChangingNation.htm
Probability of a Named Storm
http://www.aoml.noaa.gov/hrd/tcfaq/t
cfaqG.html#G12
Landfall Hurricanes
Picture Page
• http://www.usgs.gov/themes/hurricane.gif
• http://www.foe.co.uk/campaigns/climate/im
ages/hurricane.jpg
• http://jrscience.wcp.muohio.edu/coriolis/hur
ricanes.html
The Boys Who Know
it All
• Hurricane Hunters
• Red Cross Safety Tips
• Chris Landsea's FAQs