Chapter Mostly 11 Hurricanes
Tropical Weather
Noon sun is always high, seasonal temperature changes small
Daily heating and humidity = cumulus clouds and afternoon thunderstorms
Non-squall clusters loosely organized clusters of thunderstorms
Tropical squall line- Thunderstorms in the tropics align in a row of vigorous convective cells
tropical wave or easterly wave a weak trough of low pressure in the tropics that tends to move
from east to west
Seasons defined by precipitation as opposed to temperature
Instead of isobars streamlines that depict wind flow are drawn since isobars provide little useful
information in the tropics because pressure varies only slightly
Anatomy of a Hurricane
Intense storm of tropical origin with winds greater than 64 kts; typhoon, cyclone, tropical
cyclone
Eye
Eye wall
Spiral rain band
Latent heat
The Right Environment
o Tropical waters with light wind
o 26.5C sea surface temperatures (June-November)
o Surface converge trigger (tropical wave)
o Coriolis effect: 5-20 latitude
The Developing Storm
o Cluster of thunderstorms around a rotating low pressure
o As latent heat is released inside the clouds, the warming of the air aloft creates an area of high
pressure, which induces air to move outward, away from the high.
o The warming of the air lowers the air density, which in turn lowers the surface air pressure.
o As surface winds rush in toward the surface low, they extract sensible heat, latent heat, and
moisture from the warm ocean.
o As the warm, moist air flows in toward the center of the storm, it is swept upward into the clouds
of the eyewall.
o As warming continues, surface pressure lowers even more, the storm intensifies, and the winds
blow even faster.
o This situation increases the transfer of heat and moisture from the ocean surface.
Hurricane Formation and Dissipation
Hurricane Stages of Development
o Tropical Disturbance
o Tropical Depression
o Tropical Storm
o Hurricane (> 65kts)
The Storm Dies Out
o Cold water, land
Hurricanes and Mid-latitude Storms
o Hurricane warm core low
o Mid-latitude cold-core low
o Hurricane + upper level trough = mid-latitude cyclone
Hurricane movement
o General track: west, northwest, northeast
o Much variation
Naming hurricanes - Process has changed over the years:
o Name of place of landfall
o Latitude and longitude
o Letters of the alphabet
o Alphabetical names
o female Alphabetical, alternating female and male names
o Retirement (Katrina, Camille [1969, Category 5, Mississippi])
Swells-large wave that carry the energy of a storm to distant beaches
Storm surge on north side of storm (tide)
Hurricane spawned tornadoes
Saffir-Simpson scale - 1 weakest, 5 strongest
A hurricane watch issued by the National Weather Service is the best indication that a hurricane
will likely strike your area within 24 hours.
On the Saffir-Simpson scale a category 5 storm would indicate a very strong hurricane.
Most of the destruction caused by a hurricane is due to flooding.
high winds.
Storms that form in the tropics are given names when they reach tropical storm strength.
Hurricanes can't form along the equator because the Coriolis force is too small along the equator.
A weak trough of low pressure found in the tropics and along which hurricanes occasionally form
is called an easterly wave.
The vertical structure of the hurricane shows an upper-level outflow of air, and a surface inflow
of air.
The main reason hurricanes don't develop (well, one recorded) over the south Atlantic Ocean
adjacent to South America is because the surface water temperatures are too cold.
The main source of energy for a hurricane is the warm ocean water and release of latent heat
energy by condensation.
Hurricanes dissipate when they move over colder water, they move over land, or surface inflow
of air exceeds upper-level outflow of air.
Some more about tornadoes and thunderstorms:
Hamilton Crossroads, AL is the community with the tornado damage that I showed extensively in
class.
Flooding was caused by the tornado that I discussed in class (but was not in the textbook) by a
water tower that was knocked down.
An anvil cloud forms near the top of a thunderstorm where the thunderstorm cloud reaches a
stable region of the atmosphere.
The strongest tornado is one with a thick funnel cloud and a vertical orientation (unlike the whole
thunderstorm, which is strongest with a tilted updraft).
Lightning may occur from a cloud to the ground, from one cloud to another cloud & within a
cloud.
The so-called "Tornado Belt" of the United States is located in the Central Plains.
Light flashes darting upward from the tops of thunderstorms are called sprites and blue jets; I
think that I forgot to mention this in class.