Formation of a hurricane?

Question

How do hurricanes form? steps?

Answer 1

Here is an Excelent link to the formation of tropical Cyclones (Hurricanes)

http://www.srh.noaa.gov/srh/jetstream/tr...

Tropical Cyclone Introduction

A tropical cyclone is a warm-core, low pressure system without any "front" attached, that develops over the tropical or subtropical waters, and has an organized circulation. Depending upon location, tropical cyclones have different names around the world. In the:

Atlantic/Eastern Pacific Oceans - hurricanes

Western Pacific - typhoons

Indian Ocean - cyclones

Regardless of what they are called, there are several favorable environmental conditions that must be in place before a tropical cyclone can form. They are:

Warm ocean waters (at least 80°F / 27°C) throughout a depth of about 150 ft. (46 m).

An atmosphere which cools fast enough with height such that it is potentially unstable to moist convection.

Relatively moist air near the mid-level of the troposphere (16,000 ft. / 4,900 m).

Generally a minimum distance of at least 300 miles (480 km) from the equator.

A pre-existing near-surface disturbance.

Low values (less than about 23 mph / 37 kph) of vertical wind shear between the surface and the upper troposphere. Vertical wind shear is the change in wind speed with height.

Tropical Cyclone Formation Basin

Given that sea surface temperatures need to be at least 80°F (27°C) for tropical cyclones form, it is natural that they form near the equator. However, with only the rarest of occasions, these storms do not form within 5° latitude of the equator. This is due to the lack of sufficient Coriolis Force, the force that causes the cyclone to spin. However, tropical cyclones form in seven regions around the world.

See the probabilities for the Atlantic Basin by month.

One rare exception to the lack of tropical cyclones near the equator was Typhoon Vamei which former near Singapore on December 27, 2001. Since tropical cyclone observations started in 1886 in the North Atlantic and 1945 in the western North Pacific, the previous recorded lowest latitude for a tropical cyclone was 3.3°N for Typhoon Sarah in 1956. With its circulation center at 1.5°N Typhoon Vamei's circulation was on both sides of the equator. U.S. Naval ships reported maximum sustained surface wind of 87 mph and gust wind of up to 120 mph.

The seedlings of tropical cyclones, called "disturbances", can come from:

Easterly Waves: Also called tropical waves, this is an inverted trough of low pressure moving generally westward in the tropical easterlies. A trough is defined as a region of relative low pressure. The majority of tropical cyclones form from easterly waves.

West African Disturbance Line (WADL): This is a line of convection (similar to a squall line) which forms over West Africa and moves into the Atlantic Ocean. WADL's usually move faster than tropical waves.

TUTT: A TUTT (Tropical Upper Tropospheric Trough) is a trough, or cold core low in the upper atmosphere, which produces convection. On occasion, one of these develops into a warm-core tropical cyclone.

Old Frontal Boundary: Remnants of a polar front can become lines of convection and occasionally generate a tropical cyclone. In the Atlantic Ocean storms, this will occur early or late in the hurricane season in the Gulf of Mexico or Caribbean Sea.

Once a disturbance forms and sustained convection develops, it can become more organized under certain conditions. If the disturbance moves or stays over warm water (at least 80°F), and upper level winds remain weak, the disturbance can become more organized, forming a depression.

The warm water is one of the most important keys as it is water that powers the tropical cyclone (see image above right). As water vapor (water in the gaseous state) rises, it cools. This cooling causes the water vapor to condense into a liquid we see as clouds. In the process of condensation, heat is released. This heat warms the atmosphere making the air lighter still which then continues to rise into the atmosphere. As it does, more air moves in near the surface to take its place which is the strong wind we feel from these storms.

Therefore, once the eye of the storm moves over land will begin to weaken rapidly, not because of friction, but because the storm lacks the moisture and heat sources that the ocean provided. This depletion of moisture and heat hurts the tropical cyclone's ability to produce thunderstorms near the storm center. Without this convection, the storm rapidly diminishes.

The NASA image (left) is Hurricane Wilma in October 2005. Clicking the image will load a 2mb movie (provided by NASA) showing the life of the storm. The color of the ocean represents sea surface temperature with orange and red colors indicating temperatures of 82°F or greater.

As Wilma moves northwest, then eventually northeast, the water temperature decreases (indicated by the change to light blue color) after the storm passes a particular location. This is the result of the heat that is removed from the ocean and provided to the storm.

Therein shows the purpose of tropical cyclones. Their role is to take heat, stored in the ocean, and transfer it to the upper atmosphere where the upper level winds carry that heat to the poles. This keeps the polar regions from being as cold as they could be and helps keep the tropics from overheating.

There are many suggestions for the mitigation of tropical cyclones such as "seeding" storms with chemicals to decrease their intensity, dropping water absorbing material into the storm to soak-up some of the moisture, to even using nuclear weapons to disrupt their circulation thereby decreasing their intensity. Read about tropical cyclone myths. While well meaning, the ones making the suggestions vastly underestimate the amount of energy generated and released by tropical cyclones.

Even if we could disrupt these storms, it would not be advisable. Since tropical cyclones help regulate the earth's temperature, any decrease in tropical cyclone intensity means the oceans retain more heat. Over time, the build-up of heat could possible enhance subsequent storms and lead to more numerous and/or stronger events.

There has also been much discussion about the abnormally high number of storms for the 2005 Atlantic basin (27 named storms including 15 hurricanes). Compared to the age of the earth, our knowledge about tropical cyclone history is only very recent. Only since the advent of satellite imagery in the 1960's do we have any real ability to count, track and observe these systems across the vast oceans. Therefore, we will never know the actual record number of tropical cyclones in the Atlantic Oceans.

Answer 2

****   Here are the steps.  It's basically due to the heat released when the very moist air condenses to form clouds.  See the steps below:    ****

****  How it happens  ****

1.  A persistent area of rain or thunderstorms forming in the tropical oceans is the first step. When water condenses to form water in the cloud, heat is released into the immediate environment (yes, in the cloud). If this lasts for a while, eventually enough heat is released aloft to create slightly less dense air relative to areas around the storming clouds. Since the air is less dense aloft, this causes lower pressure relative to locations away from the thunderstorm cluster in the air just above the ocean surface. You can think of it this way...if you have a parcel of less dense air aloft relative to parcels to the right or left, then the weight of the air at the surface is less right underneath the less dense air. So this is the beginning of a surface low-pressure.

2.  After the weak surface low-pressure forms, wind begins converging towards the low pressure center. When it converges, it has to go somewhere...up. This keeps the storm cluster going because the updrafts of moist air keep condensing and releasing more heat (called latent heat). This keeps those thunderstorms going, and further enhances the low pressure below. You can see how this creates a feedback-effect making the surface low pressure gradually stronger and stronger.

****  Requirements for, and factors against formation: ****

There are certain things that can disrupt this process, like strong winds aloft. The strong winds aloft tend to pull this heat away from the storms and therefore makes the surface low-pressure formation less effective. During the summer, the atmosphere is usually very calm aloft in tropical ocean regions.  (Extra:  The calm winds aloft is a consequence of what is called a 'barotropic' atmosphere by meteorologists.)

Also, this process is much more efficient when water temps are warmer. When water temps are warmer, the temp of the atmosphere above it tends to match, and warmer air can hold more water vapor. During the initial formation, this very moist air is entrained into the updrafts that I mentioned before. With more moisture, there is more condensation, and more heat release. So the warmer the ocean, the more efficient this formation process is.

(see link below for an image of the ITCZ I'm about to mention)

Finally, there is an area in the tropics called the Inter-tropical Convergence Zone (ITCZ) that migrates well north of the equator during the northern hemisphere summer. Across the earth from north to south there are alternating latitudes of favored wind convergence and the opposite, divergence. The ITCZ is the convergence band in the tropics. Because the wind is convergent at the surface the air must eventually rise, and so there's a huge band of updrafts and persistent showers. This is often the birthplace of hurricanes when this moves far enough north of the equator since the persistent shower/thunderstorm criteria is already a given. But a hurricane can also form off the tail end of a front as it slows down and gradually dissipates in the subtropics (usually how early season hurricanes form close to the U.S. in the gulf of Mex or say near or just north of the Bahamas, like in June).

Why must it be away from the equator? The hurricane formation process requires at least a little 'Coriolis effect,' and the Coriolis effect is zero at the equator, and generally too small within about 5 degrees north or south of it.

So all these three conditions come together during the summer.

Answer 3

http://www.windows.ucar.edu/tour/link=/e...

hope this helps lol

Answer 4

1. Warm ocean waters (of at least 26.5°C [80°F]) throughout a sufficient depth (unknown how deep, but at least on the order of 50 m [150 ft]). Warm waters are necessary to fuel the heat engine of the tropical cyclone.

2. An atmosphere which cools fast enough with height such that it is potentially unstable to moist convection. It is the thunderstorm activity which allows the heat stored in the ocean waters to be liberated for the tropical cyclone development.

3. Relatively moist layers near the mid-troposphere (5 km [3 mi]). Dry mid levels are not conducive for allowing the continuing development of widespread thunderstorm activity.

4. A minimum distance of at least 500 km [300 mi] from the equator. For tropical cyclogenesis to occur, there is a requirement for non-negligible amounts of the Coriolis force to provide for near gradient wind balance to occur. Without the Coriolis force, the low pressure of the disturbance cannot be maintained.

5. A pre-existing near-surface disturbance with sufficient vorticity and convergence. Tropical cyclones cannot be generated spontaneously. To develop, they require a weakly organized system with sizable spin and low level inflow.

6. 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. Large values of vertical wind shear disrupt the incipient tropical cyclone and can prevent genesis, or, if a tropical cyclone has already formed, large vertical shear can weaken or destroy the tropical cyclone by interfering with the organization of deep convection around the cyclone center.