 | In-Depth Hurricane Information | |
 | Below is hurricane information pertaining to almost every aspect of a hurricane. Enjoy this vast wealth of data and check back as information will be continously added as the science of Hurricane Meteorology is a large and growing one! | |
New! Hurricane warning north atlantic archive!
The archive will eventually have a page for every storm in the atlantic ever recorded!
Each page will include a meteorological analysis, damage overview, radar data,
satellite data, and various tracking data as well as a satellite image representative of
the storm.
North Atlantic Archives
Visit the WeatherCore Forecasting Tutorial for information on
tropical cyclone forecasting. Read the one on this page first though to understand the tropical cyclone.
WeatherCore Forecasting Tutorial
The Tropical Cyclone
Hurricanes are basically a very mature
stage of the tropical cyclone. Tropical Cyclones are defined as a
non-frontal synoptic scale low pressure system over tropical or sub-tropical
waters with a definite surface circulation. This is the basic theory
of tropical cyclones but, there are variations. Sub-Tropical
cyclones for example basically meet these criteria but, they
also have many traits of a mid-lattitude system such as a large
windfield. Another variation is extratropical cyclones. Extra
tropical cyclones also meet the requirements but, they recieve
thier energy from temperature difference unlike tropical
cyclones which recieve thier energy from cloud and rain
formation. Read on to learn more.
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| Tropical Cyclone | Sub Tropical Cyclone | Extra Tropical Cyclone |
Tropical Cyclone Formation
Even though tropical cycones may grow into forces
of nature with unmatched power, they do start subtly. It all begins
when a impulse of energy such as an easterly wave from Africa
travels over an area of ocean of about 80 degrees or more. (This
temperature pretty much marks the threshold for energy needed
to produce a tropical cyclone.) The water must be 50 meters deep
also. The atmosphere also must be moist because dry air severely
inhibits development and there must be low atmospheric shear.
The final requirement is the point of generation must be 500 km
from the equator because if its closer there will be no spinning due
to the coriolis effect. If all these requirements are meant the impulse
will start to generate convection and the tropical cycone formation
would begin.
The above image shows convection developing which is the
beginning of Tropical Cyclone formation. Image courtesy of
Steven Maciejewski.
Tropical Disturbance
As the convection becomes more widespread and long
lasting a tropical disturbance is born. A tropical disturbance
is defined as being an area of convection from 200 to 600 km
in diameter that has originated in the tropics or sub tropics and
moves with a non frontal character. The most important thing
is it must mantain itself for 24 hours but, it doesnt need to have
a windfield. Most disturbances die but, a lucky few with the
right ingredients develop a spin due to the coriolis effect and
strengthen into tropical depressions.
The above image shows a tropical disturbance. Notice the
wealth of convection but, lack of orginization.
Tropical Depression
Once the disturbance has an estabilished windfield and
a closed surface circulation, a tropical depression is born. Depressions have
anywhere from 25 to 38 mph winds. Usually at this stage features typical to a
tropical cyclone such as spiral bands form. If conditions remained right the
depression will continue to strenghten torwards tropical storm status.
The above image shows a tropical depression. Notice more centralized
organization and signs of a surface circulation.
Tropical Storm
As winds increase above 38 mph in a tropical
depression, a tropical storm is born. A tropical storm is a tropical
cyclone with winds from 39 to 73 mph. At this stage outer rainfall
bands become very distinct. Tropical storms are also the first
dangerous level of a tropical cyclone. They can cause many utilities
to fail and damage property.
The above image shows a tropical storm. Notice the very distinct banding
and surface circulation.
Hurricane
When a tropical storm finally breaks the 73 mph
barrior a hurricane is formed. At this stage eye features
such as the eye and eyewall develop. Banding also becomes much more organized
and a central dense overcast forms. Hurricanes are infamous for thier power
as they have caused massive destruction across the globe. Hurricane
winds are 74+ mph but, they are divided into 5 categories. Categories
1 and 2 represent typical hurricanes but, are still powerful. A storm can
strengthen far beyond cat 2 though when the ingredients are just right.
The image above shows a regular hurricane . Notice the distinct eye features
and banding. However it is not even close to perfect as told by its lopsided
convection.
Major Hurricane
When a hurricane breaks the 115 mph mark a major
hurricane is born. At this stage the features of a tropical cyclone fully mature
and become nearly perfect. This represents category 3 to 5 hurricanes which
cause by far the most devestation. Major hurricanes can break the 200 mph
mark rarely and that represents the absolute strongest tropical cyclone
possible. Ingredients need to be near perfect for major hurricane formation.
The image above shows a major hurricane. Notice how all features in the
storm have become nearly perfect and it looks like a textbook hurricane.
Tropical Cyclone Inhibitors
Even though hurricanes are one of the most powerful
weather systems on Earth, they can still be weakened, destroyed, or prevented
by many factors. The biggest weakener of tropical cyclones
is land. When a tropical cyclone hits land its essentially like not giving your
car gas. Same thing goes for cold (<80 degree) water, except its more drawn out.
If the tropical cyclone is over land for too long, it will die.
Another land feature that destroys tropical cyclones even faster is mountains.
Mountains rip into the anatomy of a tropical cyclone and can destroy a tropical
cyclone rapidly. A good example is any tropical cyclone passing over
Hispanolia. Land features are not the only problem for tropical cyclones
however. Atmospheric inhibitors have much more variety and sometimes more
power. The greatest atmospheric inhibitor is wind shear. Wind shear is
variance in wind at different altitudes and basically elongates or cuts a cloud
depending on strength. A tropical cyclone can only form in less than 20kt
shear and if it gets above that no tropical cyclones can form as they will
be blown apart. Any existing cyclones would rapidly die. Another well
known inhibitor of tropical cyclones is dry air. Dry air can come from many
sources like the saharan desert which produces the SAL. This air layer
rapidly weakens hurricanes when it enters a storm. This goes for all
dry air. Another inhibitor of tropical cyclones is the Earth's spin. This
effect known as the coriolis effect makes a 1000 km no hurricane zone
on the equator. Thus, there are many factors that inhibit tropical cyclones
and make the job of forecasting intensity difficult to say the least!
The image above shows a tropical cyclone being inhibited by shear. This shows how strong of an effect some inhibiting factors can have on a tropical cyclone.
Tropical Cyclone Features
A tropical cyclone is a very complex weather system.
It has many features which all play a vital role in the development and
in the maintaining of the storm system. Below are the many features
that make up a tropical cyclone.
Surface Low
The surface low of a tropical cyclone is a pivital
component to providing energy and initiating a tropical cyclone. Since the
surface low is essentially an area of lower pressure air flows in torwards it
in a cyclonic effect. This effect is clockwise in the southern hemisphere and
counterclockwise in the northern hemisphere. This results in moisture being
drawn torwards the center of the tropical cyclone which along with the low
pressure results in a more favorable environment for convection. This then
strengthens the surface low and a feedback loop is made. Another
important aspect of the surface low is its at the surface. This results in the
strongest winds at the surface and thus, the damaging effect of tropical
cyclone wind.
This above image shows a tropical cyclone with a well defined surface low.
The Warm Core Engine
The warm core engine is what produces the massive
amounts of energy released by tropical cyclones and without it no tropical
cyclone could exist. The first step of the engine is moisture rising and
condensing when it hits the cold upper atmosphere. When this happens
energy is release due to physics and gives more energy into the storm.
This will then draw in more moisture and make a feedback loop. This
effect also makes the storm warmer than its surroundings and it thus,
is called a warm core. Also, the dry air produced after condensation
is called outflow and it vents out over the top of the storm. This is
vital to the engine.
This above image shows the process of a warm core tropical cyclone engine.
Spiral Bands
Spiral bands radiate outwards from the eyewall and form a spinning area of rain near the center of the storm.
As they get farther away from the storm however, breaks form in the spiral bands due to subsidence from
the top of the band. These gaps of subsidence become bigger as one travels from
the storm. The spiral bands are comprised of powerful and rapidly moving
thunderstorm cells that form near the eyewall and dissipate at the end of the
bands many hundreds of miles away. Spiral bands can have very strong winds due
to thier rapid movement combined with the associated wind field.
This above radar animation shows spiral bands spiraling outwards from the eyewall with associated cells.
Outflow and Subsidence
As mentioned earlier the warm core engine creates a
dry air exhaust known as outflow. Subsidence is also created which creates a
no cloud zone around a hurricane and in the eye(maybe). This
is very important to the mantaining of the storm system because if the outflow
was restricted energy lacking air would be trapped in the storm(dry air) and
the storm would be suffocated. On an interesting note, spiral bands make
thier own subsidence much the sameway as a whole hurricane does except
on a smaller scale.
This above image shows the outflow of a tropical cyclone. The outflow can be identified through the blue arrows which show outfow strength and direction.
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The Eye and Eyewall
The eyewall is a small circular band of convection
where the strongest winds in the hurricane exist. It surrounds the
eye of the hurricane. The eye is an area of relative calm in the hurricane surrounded by
the eyewall. The eye is believed to be produced by 1 0f 2 theories: the mass
is centrifuged out of the eye into the eyewall causing calm. The other one is subsidence
from eyewall convection creates an area of calm in the eye. Subsidence
stops 1-3 km above the surface in the eye sometimes making a stadium
effect. Sometimes 2 eyewalls form but, the inner eyewall collapses into
the eye from outer eyewall subsidence causing cyclone weakening. The
eye and eyewall of a hurricane are some of the most unique features to
a hurricane.
The above image shows a look inside the eye. The eyewall is surrounding it and there is an area of calm in the middle.