Hurricanes: The Evil WindAnthony R. Lupo

Department of Soil, Environmental, and Atmospheric Science

302 E ABNR BuildingUniversity 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 A M J J A S O N D Tot

Subtrop.

1 2 1 4

Depres.

2 6 7 11 3 3 32

Trop. S. 1 6 9 12 21 7 2 58Cat 1 6 3 2 2 13Cat 2 1 5 6 3 15Cat 3 1 4 2 1 8Cat 4 1 2 3Cat 5

Total 1 3 12 17 39 37 16 4 129

Hurricanes: The Evil Wind• Tropical Entities passing within 250

miles of Birmingham, AL since 1938. F M A M J J A S O N D Tot

Subtrop.

0

Depres.

4 5 6 6 2 23

Trop. S. 2 1 3 6 2 14Cat 1 1 3 2 1 7Cat 2 1 1Cat 3 1 1Cat 4Cat 5

Total 6 7 12 16 5 46

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