Hurricanes: The Evil Wind
Anthony R. Lupo
Department of Soil, Environmental, and Atmospheric Science
302 E ABNR Building
University of Missouri – Columbia
Columbia, MO 65211
Hurricanes: The Evil Wind
• Hurricanes are a tropical system, which have a
unique structure, and, sometimes, unique
behavior.
• “Hurricane” is a Spanish/French/Indian word
literally meaning “evil wind”
• In the Atlantic, there are typically 6 hurricanes
and 10 named storms. They typically last for 5 10 days.
Hurricanes: The Evil Wind
• Hurricanes have a special structure, one
that is quite different from mid-latitude
storms.
• There is no frontal structure in tropical
systems and they are “warm core”. That
is, they are warmer in the center than in
the surroundings.
Hurricanes: The Evil Wind
Hurricanes: The Evil Wind
• They also need an atmosphere with very little
wind shear (in the vertical) to exist. Otherwise,
the circulation can be disrupted.
• Hurricanes are sustained by the release on heat
due to condensation. They are a convective
engine.
• They are “spun down” over land by frictional
forces.
Hurricanes: The Evil Wind
• In summary, they need:
– A pre-existing area of low pressure.
– An atmosphere with little shear
– Waters of 80o F (26o C) or more.
Hurricanes: The Evil Wind
• Hurricane movement is generally east to west in
the tropics, but in the vicinity of North America
are influenced heavily by mid-latitude
circulations.
• Winds in a deep layer (850 hPa – 200 hPa), 1
mile – 6 miles up, influence their movement.
• Models now doing a good job with their
movement.
Hurricanes: The Evil Wind
• Terminology:
• Tropical “wave” – is an area of low pressure and
thunderstorms with strong gusty winds, and no
“closed” center.
• Tropical depression – has sustained winds of up
to 35 kts (39 mph), and a closed “cold” center of
low pressure.
Hurricanes: The Evil Wind
• Tropical storm – storm acquires a name,
and winds are sustained from 35 – 65 kts
(39 – 74 mph). At this point, they are
warm core storms.
• Hurricane – acquires an eye and sustained
winds over 65 kts (74 mph).
Hurricanes: The Evil Wind
• Tropical Entities passing within 250 miles
of Norfolk, VA since 1938.
F
M
J
Subtrop.
1
2
Depres.
2
6
7
11
3
3
6
9
12
21
7
2
58
6
3
2
2
13
5
6
3
15
4
2
1
8
1
2
Trop. S.
M
A
1
J
Cat 3
Cat 4
Cat 5
1
1
S
O
N
1
Cat 1
Cat 2
A
D
Tot
4
32
3
Hurricanes: The Evil Wind
• Tropical Entities passing within 250 miles
of Birmingham, AL since 1938.
F
M
A
M
J
J
A
S
O
Subtrop.
N
D
Tot
0
Depres.
4
5
6
6
2
23
Trop. S.
2
1
3
6
2
14
1
3
2
1
7
Cat 1
Cat 2
1
1
Cat 3
1
1
Cat 4
Cat 5
Hurricanes: The Evil Wind
• Since 1938, 1961-1969 was the longest
“threat free” period, and the 1960’s the
quietest decade with 2 storms. The 1980s
were not far behind with only 3 events.
• The year of 2005 was the worst, 5 storms
pass within 250 miles of Birmingham.
(August 2004, 2 storms!)
Hurricanes: The Evil Wind
• During the 1960s through 1990s, there
were only 15 events (mean 4 storms per
decade). During the “oughts” (2000s),
there were 15 storms.
• Tropical storm threat is greatest in
September. Season gears up in June and
winds down by mid-October.
Hurricanes: The Evil Wind
• Ivan (2003) – In AL, none dead and $2.0
B in damage.
Hurricanes: The Evil Wind
• Frederic (1979) – costliest hurricane in US
history up to 1989.
Hurricanes: The Evil Wind
• Eloise (Sept 1975) remained a Category 3
well inland, brought torrential rains and
much flooding along the east coast.
Hurricanes: The Evil Wind
• "Preparation through education is less costly than learning through
tragedy.“ - MAX MAYFIELD, DIRECTOR NATIONAL HURRICANE CENTER
• Hurricane Watch – hurricane conditions could
happen at your location in 36 hours.
• Hurricane Warning – hurricane conditions are
expected within 24 hours.
• Source: (http://www.nhc.noaa.gov/) National
Hurricane Center
Hurricanes: The Evil Wind
• Storm surge and heavy rains are the
biggest killers in a hurricane, not winds,
lightning, or tornadoes.
• People should be aware that they should
take any tropical system seriously. Some
of the biggest killers have not been
hurricane intensity.
Hurricanes: The Evil Wind
• Hurricane numbers during a season are
impacted by El Nino. El Nino can influence the
atmospheric ingredients mentioned earlier.
• There tend to be fewer / less intense hurricanes
in an El Nino year. This is mainly because of the
inactive Gulf and Caribbean.
Hurricanes: The Evil Wind
• Upper tropospheric trough!
Hurricanes: The Evil Wind
• Hurricane numbers also fluctuate on the
decadal time-scale, especially since the El
Nino in influenced in this manner.
• There is little long term trend in Atlantic or
Pacific hurricane numbers.
Hurricanes: The Evil Wind
• Are there more severe hurricanes?
• Long term, the ratio of Cat 3 – 5 storms
to all storms is 42%
• In 2000 – 2009, this ratio was 49%, a bit
higher.
Hurricanes: The Evil Wind
• All things being equal, warmer waters will
cause more and stronger hurricanes, but
remember, these storms need a
cooperative ocean and atmosphere.
• There is no evidence climate change is
leading to more hurricanes.
Hurricanes: The Evil Wind
• Check this out………
• 2005 (27) versus
1933 (21)
Hurricanes: The Evil Wind
• Questions?
• Comments?
• Criticisms?
• LupoA@missouri.edu
Hurricanes: The Evil Wind