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Resource Section for Meteorology
| Temperature | Clouds | Precipitation | Wind | Atmospheric Pressure | |Humidity&Dew point | Forecasting | Hurricanes /Typhoon /Cyclones | |Snowstorms | Thunderstorms | Tornadoes | Global Issues | Glossary |
| Hurricanes | How are Hurricanes formed | Development of Hurricanes| |Stages of Development | Movement of Hurricanes |Destruction from Hurricanes| |Saffir-Simpson Hurricane Damage |Watch and Warning | Average number of Tropical Storms| Hurricane Checklist | Quiz | Credits |
Hurricanes are large tropical storms with heavy winds. By definition, they contain winds in excess of 74 miles per hour (119 km per hour) and large areas of rainfall. In addition, they have the potential to spawn dangerous tornadoes. The strong winds and excessive rainfall also produce abnormal rises in sea levels and flooding.
The ocean-water temperature has to be above 79 degrees F in order for a hurricane to be generated, so they normally form in late summer and early fall when the conditions are right. Meteorologists use the term tropical storm when a storm's winds are under 74 miles per hour, and hurricane when the wind speed rises. A hurricane has a peaceful center called the eye, that is often distinctive in satellite images. The eye stretches from 10 to 30 miles wide and often contains calm winds, warm temperatures and clear skies. Around this tropical bliss is a frenzy of winds gusting at speeds up to 186 miles per hour. If one percent of the energy in one hurricane could be captured, all the power, fuel, and heating requirements of the United States could be met for an entire year. It takes 500 trillion horsepower to whirl the great core of winds at such tremendous speeds. It is the equivalent of explodin Anatomy of a Hurricane spiral rain bands, the eye wall and the eye
Convective Processes and their role in the development of hurricanes When a cold air mass is located above an organized cluster of tropical thunderstorms, an unstable atmosphere results. This instability increases the likelihood of convection, which leads to strong updrafts (red arrows) that lift the air and moisture upwards, creating an environment favorable for the development of large cumulonimbus clouds. A tropical disturbance is born, the first stage of a developing hurricane.
Animation by: Shao Surface convergence (pink horizontal arrows in animation below) causes rising motion around a surface cyclone (labeled as "L"). The air cools as it rises (red vertical arrows) and condensation occurs, which releases latent heat into the atmosphere. This heating causes air to expand, creating an area of high pressure aloft. The force resulting from the established pressure gradient causes air to diverge at upper levels (red horizontal arrows).
Animation by: Shao Since pressure is a measure of the weight of the air above a unit area, removal of air at upper levels subsequently reduces pressure at the surface. A further reduction in surface pressure leads to increasing convergence (due to an intensified pressure gradient), which further intensifies the rising motion, latent heat release, and so on. As long as favorable conditions exist, this process continues to build upon itself, ultimately resulting in the development of a hurricane.
Stages of Development from disturbance to hurricane Hurricanes evolve through a life cycle of stages from birth to death. A disturbance graduates to a more intense stage of development by attaining a specified sustained wind speed.
steered by the global winds The global wind pattern is also known as the "general circulation" and the surface winds of each hemisphere are divided into three wind belts:
The easterly trade winds of both hemispheres converge at an area near the equator called the "Intertropical Convergence Zone (ITCZ)", producing a narrow band of clouds and thunderstorms that encircle portions of the globe. The path of a hurricane greatly depends upon the wind belt in which it is located. A hurricane originating in the eastern tropical Atlantic, for example, is driven westward by easterly trade winds in the tropics. Eventually, these storms turn northwestward around the subtropical high and migrate into higher latitudes. As a result, the Gulf of Mexico and East Coast of the United States are at risk to experience one or more hurricanes each year.
In time, hurricanes move into the middle latitudes and are driven northeastward by the westerlies, occasionally merging with mid-latitude frontal systems. Hurricanes draw their energy from the warm surface water of the tropics, which explains why hurricanes dissipate rapidly once they move over cold water or large land masses.
Damage caused by hurricanes With hurricanes being as powerful as they are, it is not surprising that upon landfall they cause damage and destruction. Even when the hurricane has yet to make landfall, its effects can be dangerous. However, most of the damage caused to man and nature occur as a hurricane makes landfall.
Saffir- Simpson Hurricane Damage- potential: The Saffir-Simpson Hurricane Scale is a 1-5 rating based on the hurricane's present intensity. This is used to give an estimate of the potential property damage and flooding expected along the coast from a hurricane landfall. Wind speed is the determining factor in the scale, as storm surge values are highly dependent on the slope of the continental shelf and the shape of the coastline, in the landfall region. Note that all winds are using the U.S. 1-minute average.
Average number of tropical storms in each year : There are an average of 85 tropical storms and 45 hurricanes/ typhoons globally per year : and about nine named storms form per year in tropical Atlantic and Gulf of Mexico area, with around six of those becoming hurricanes and two of those becoming intense hurricanes ( those with sustained winds exceeding 130mph or 209 km/hr). With 19 named storms in Atlantic and Gulf of Mexico, 1995 became the second busiest hurricane season on record
What are the Hurricane tracking models and how do they forecast ? The National Hurricane Center (NHC) in Coral Gable ,Florida is a part of the National Weather Service under the National Oceanic and Atmospheric Administration, an agency of U.S Department of Commerce. The NHS tracks tropical cyclones from the tropical depression stage through the hurricane stage over the north Atlantic Ocean , Caribbean Sea, Gulf of Mexico and eastern Pacific Ocean and makes predictions of the future position and intensity of the cyclones. To forecast the track and intensity of tropical cyclones .NHC uses mathematical computer models. These models represent the tropical cyclone and its environment in a greatly simplified manner. Computers running these models can forecast the future motion and intensity of a cyclone. Hurricane forecasters then interpret model results to arrive at a final track and intensity forecast ,distributing it to the public in the form of advisories. The mathematical models used at NHC are three basic types : Statistical ,Dynamical or Combination (Statistical and Dynamical together ).Statistical models forecast the future by using current information about the hurricane and comparing it to historical knowledge about the behavior of similar tropical cyclones . The historical record for storms over the north Atlantic begins in 1871, while the record for storms for the east Pacific extends back to 1945. Dynamical models work differently . They are designed to use the results of global atmospheric model forecasts in different ways to forecast tropical cyclone motion and intensity .Global models take current wind ,temperature ,pressure and humidity observations and make forecasts of the actual atmosphere in which the cyclone exists. Because of their mathematical simplicity ,both types of models are incomplete :Statistical models ignore current atmospheric conditions ,and Dynamical models ignore the behavior of historical storms. Combination models, however , can be constructed to capitalize on the strengths of each . Because of their simplicity ,statistical models were designed first for tropical cyclone forecasting in the lat 1960s. In the early seventies ,combination models were developed as global models began making forecasts in tropical regions .As computers became more powerful , global models improved and pure dynamic models are beginning to dominate the accuracy race . This is particularly true when tropical cyclones approach data-rich regions close to the continents where the state of the atmospheric environment is adequately observed and well -know n. Over oceanic areas , far removed from land ,combination models are still the best performers
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Christopher
Columbus was the first European in modern times to write about the
hurricane. The Indians of Guatemala called the god of stormy weather "Hunrakan."
Similar names were probably present throughout the Caribbean. Captain
Fernando de Oviedo gave storms their modern name when he wrote "So when the
devil wishes to terrify them, he promises them the 'Huracan,' which means
'tempest.'" The same storms in other parts of the world are known as
typhoons, baqulros, Bengal cyclones and willy-willies.
Left:
Image produced by Hasler, Pierce, Palaniappan & Manyin
of NASA's Goddard Laboratory for Atmospheres - Data from NOAA 
