World Meteorological Organization, Report No. TCP; Geneva, Switzerland, 62 pp. Tropical cyclones tend to be symmetrical. This means the winds should be the same in all quadrants at a given distance from the center. If a hurricane is moving to the west, the right side would be to the north of the storm, if it is heading north, then the right side would be to the east of the storm. For example, a hurricane with 90mph winds moving at 10mph would have a mph wind speed on the forward-moving side and 80 mph on the side with the backward motion.
The energy released from a hurricane can be explained in two ways: the total amount of energy released by the condensation of water droplets latent heat , or the amount of kinetic energy generated to maintain the strong, swirling winds of a hurricane. The vast majority of the latent heat released is used to drive the convection of a storm, but the total energy released from condensation is times the world-wide electrical generating capacity, or 6.
If you measure the total kinetic energy instead, it comes out to about 1. Reference: Emanuel, K. There are no other planets known to have warm water oceans from which true water cloud hurricanes can form.
However, many astronomers and planetary meteorologists believe gas giant planets such as Jupiter and Saturn exhibit similar storms. The principal candidate is the famous Great Red Spot GRS on Jupiter, and the numerous whorls that surround it, where ammonia takes the place of water.
The GRS exhibits an anticyclonic circulation at its top, just as tropical cyclones do at the top of the troposphere. On Saturn, a polar storm has been spotted by the Cassini spacecraft measuring up to 1, miles in diameter, about 20 time larger than an Earthly hurricane with winds four times stronger. On Mars, a large, cyclonic cloud feature forms every year in the northern hemisphere. It forms in the morning and dissipates by the afternoon.
Over 3, extrasolar planets have been found to date, but no others are confirmed to have convectively driven storms. However, there is reason to believe such storms exist on extrasolar planets as well. When the Weather Bureau organized its new hurricane warning network in it scheduled a special telegraph line to connect the various centers to run from June 15th through November 15th.
These changes made the Atlantic hurricane season six months long and easier for people to remember. Maximum activity occurs in early to mid September. The Northwest Pacific basin has tropical cyclones occurring all year round regularly.
There is no official definition of typhoon season for this reason. The North Indian basin has a double peak of activity in May and November though tropical cyclones are seen from April to December. References: Neumann, C. Jarvinen, C. McAdie, and J. The best time to prepare is before hurricane season begins. Make a plan for you and your family about what to do if a hurricane threatens.
Put together a hurricane kit. Ensure your house is up to code, and check for problems, such as overhanging branches or missing roof tiles. Check your shutters and other window and door coverings. Once the season begins, stay informed. Check the outlook every day, and if anything is threatening keep updated on the latest advisories. The mean annual damage from hurricanes in the US is 9. Hurricane damage varies greatly from year to year, depending on the number and strength of hurricanes making landfall, but there does not seem to be a long-term trend in adjusted damage over the last century.
There is very little association between the physical size of a hurricane and its intensity. A big hurricane does not have to be an intense one and vice versa. The damage a hurricane can cause is a function of both its maximum sustained wind and the extent of the hurricane force winds. A broad, weak storm may cause as much damage as a small, strong one. It is false to think that damage is linear with wind speed, that a mph winds will cause twice the damage as a mph winds. The relationship is exponential, and not linear.
A category 5 storm could cause up to times the damage of a category 1 hurricane of the same size. References: Weatherford, C. Pielke, Jr. Forecasting, 13, pp. Just as every person is an individual, every hurricane is different. So every experience with such a storm will be unique. The summary below is of a general sequence of events one might expect from a Category 2 hurricane approaching a coastal area.
What you might experience could be vastly different. Hurricane forecasters estimate tropical cyclone strength from satellite using a method called the Dvorak technique. Vern Dvorak developed the scheme in the early s using a pattern recognition decision tree Dvorak , If infrared satellite imagery is available for Eye Patterns generally the pattern seen for hurricanes, severe tropical cyclones and typhoons , then the scheme utilizes the difference between the temperature of the warm eye and the surrounding cold cloud tops.
The larger the difference, the more intense the tropical cyclone is estimated to be. CI numbers have been calibrated against aircraft measurements of tropical cyclones in the Northwest Pacific and Atlantic basins. On average, the CI numbers correspond to the following intensities:. Note that this estimation of both maximum winds and central pressure assumes that the winds and pressures are always consistent.
The reason that lower pressures are given to the Northwest Pacific tropical cyclones in comparison to the higher pressures of the Atlantic basin tropical cyclones is because of the difference in the background climatology. The Northwest Pacific basin has a lower background sea level pressure field.
Thus to sustain a given pressure gradient and thus the winds, the central pressure must accordingly be smaller in this basin. The errors for using the above Dvorak technique in comparison to aircraft measurements taken in the Northwest Pacific average 10 mb with a standard deviation of 9 mb Martin and Gray Atlantic tropical cyclone estimates likely have similar errors.
Thus an Atlantic hurricane that is given a CI number of 4. These would be typical ranges to be expected; errors could be worse. However, in the absence of other observations, the Dvorak technique does at least provide a consistent estimate of what the true intensity is. While the Dvorak technique was calibrated for the Atlantic and Northwest Pacific basin because of the aircraft reconnaissance data ground truth, the technique has also been quite useful in other basins that have limited observational platforms.
However, at some point it would be preferable to re-derive the Dvorak technique to calibrate tropical cyclones with available data in the other basins. Lastly, while the Dvorak technique is primarily designed to provide estimates of the current intensity of the storm, a 24 h forecast of the intensity can be obtained also by extrapolating the trend of the CI number. Whether this methodology provides skillful forecasts is unknown.
References: Dvorak, V. Dvorak, V. Fitzpatrick, P. Knaff, C. Landsea, and S. Forecasting , 10, pp. Martin, J. Forecasting , 8, pp. Each method has advantages and draw backs. Post-storm analysis of storm surge requires resolving differences in what each measures in order to find the best approximation of the surge heights.
A network of long-term, continuously operating water level stations located throughout the U. They are created by foam, seeds, and other debris. Survey crews deploy after a storm, locate, and record reliable high-water marks. GPS methods are used to determine the location of these marks, which are then mapped relative to a vertical reference datum.
Pressure Sensors USGS These are temporary water-level and barometric-pressure sensors which provide information about storm surge duration, times of surge arrival and retreat, and maximum depths. Some important terms from that glossary are below. Hurricane Watch — A Hurricane Watch is an announcement that hurricane force winds are possible within the specified area in association with a tropical cyclone.
A hurricane watch is issued 48 hours in advance of the anticipated onset. Hurricane Warning — Hurricane warnings are issued 36 hours in advance and are announced when hurricane force winds are expected somewhere within the specified area in association with a cyclone. This warning can remain in effect in the face of other hazards, such as flooding even if the winds drop to below hurricane force. Advisory — An advisory contains all tropical cyclone watches and warnings in effect along with details concerning tropical cyclone locations, intensity and movement, and precautions to be taken.
Maximum sustained wind — This is determined as winds that last for an average of at least one minute at the surface of a hurricane or about 33 feet 10 meters. Gusts — are classified as a second burst of wind higher than the maximum sustained wind.
Storm Surge Watch — A storm surge watch is the possibility of a life-threatening inundation from rising water moving inland from the shoreline, and it is usually issued 48 hours from the anticipated event in association with an ongoing tropical storm. Storm Surge Warning — The danger of a life-threatening inundations from rising water moving inland, and usually issued 36 hours in advance of the event in association with an ongoing tropical storm.
Storm Intensity — Hurricane intensity refers to the amount of energy a hurricane is carrying with it. Hurricane intensity and size are not closely related. Reference: Powell, M. Houston, and T.
The Atlantic Oceanographic and Meteorological Laboratory AOML supports these organizations by doing hurricane research with both observations and model experiments in order to provide guidance and integrate new technology into the forecast models. These experimental models are tested rigorously and submitted to the NCEP for verification before they are integrated into the operational models and sent to the NHC for use in the public forecast.
There are a number of different seasonal forecasts currently being issued for various basins. Some of these are fairly new, while the oldest and most well known Prof. The major hurricane track forecast models run operationally for the Atlantic, Eastern Pacific, and Central Pacific hurricane basins are:.
The full list of models used in the Atlantic and Eastern and Central Pacific is available to download here. Various types of consensus models ensemble means are available from these models.
Despite the variety of hurricane track forecast models, there are only a few models that provide operational intensity change forecasts for the Atlantic and Eastern and Central Pacific basins:. Information on the performance of these models is available after each season here. References: Aberson, Sim D. Marks, D. Meteorological Center; Camp Springs, Maryland, 89 pp.
Lord, S. Bender, M. Ross, R. Tuleya, and Y. Gopalakrishnan, S. Goldenberg, T. Quirino, X. Zhang, F. Marks, K-S Yeh, R. Atlas, V. Forecasting , 27, pp. Radford, A. Fiorino, M. Goerss, J. Jensen, E. Harrison, Jr. Jarvinen, B. NS NHC , 22pp. DeMaria, M. Forecasting , 9, pp. The U. It was an ambitious experimental program of research on hurricane modification carried out between and The proposed modification technique involved artificial stimulation of convection outside the eyewall through seeding with silver iodide.
The invigorated convection, it was argued, would compete with the original eyewall, lead to the reformation of the eyewall at larger radius, and thus, through partial conservation of angular momentum, produce a decrease in the strongest winds. Modification was attempted in four hurricanes on eight different days. These promising results came into question in the mids because observations in unmodified hurricanes indicated:. For a couple decades NOAA and its predecessor tried to weaken hurricanes by dropping silver iodide — a substance that serves as an effective ice nuclei — into the rainbands of the storms.
The experiments took place over the open Atlantic far from land. The idea was that the silver iodide would enhance the thunderstorms of a rainband by causing the supercooled water to freeze, thus liberating the latent heat of fusion and helping a rainband to grow at the expense of the eyewall.
With a weakened convergence to the eyewall, the strong inner core winds would also weaken quite a bit. Neat idea, but in the end it had a fatal flaw. This phenomenon makes it almost impossible to separate the effect if any of seeding from natural changes. No wonder the first few experiments were thought to be successes.
A special committee of the National Academy of Sciences concluded that a more complete understanding of the physical processes taking place in hurricanes was needed before any additional modification experiments.
Reference: Willoughby, H. Jorgensen, R. Black, and S. There have been numerous techniques that have been considered over the years to modify hurricanes: seeding clouds with dry ice or silver iodide, reducing evaporation from the ocean surface with thin-layers of polymers, cooling the ocean with cryogenic material or icebergs, changing the radiational balance in the hurricane environment by absorption of sunlight with carbon black, flying jets clockwise in the eyewall to reverse the flow, exploding the hurricane apart with hydrogen bombs, and blowing the storm away from land with giant fans, etc.
As carefully reasoned as some of these suggestions are, they all share the same shortcoming: They fail to appreciate the size and power of tropical cyclones. For example, when Hurricane Andrew struck South Florida in , the eye and eyewall devastated a swath 20 miles wide. The heat energy released around the eye was 5, times the combined heat and electrical power generation of the Turkey Point nuclear power plant over which the eye passed.
The kinetic energy of the wind at any instant was equivalent to that released by a nuclear warhead. Human beings are used to dealing with chemically complex biological systems or artificial mechanical systems that embody a small amount by geophysical standards of high-grade energy. Because hurricanes are chemically simple —air and water vapor — introduction of catalysts is unpromising.
The energy involved in atmospheric dynamics is primarily low-grade heat energy, but the amount of it is immense in terms of human experience. About 80 of these disturbances form every year in the Atlantic basin, but only about 5 become hurricanes in a typical year.
There is no way to tell in advance which ones will develop. Maybe the time will come when men and women can travel at nearly the speed of light to the stars, and we will then have enough energy for brute-force intervention in hurricane dynamics. Until then, perhaps the best solution is not to try to alter or destroy the tropical cyclones, but just learn to co-exist with them. Since we know that coastal regions are vulnerable to the storms, building codes that can have houses stand up to the force of the tropical cyclones need to be enforced.
The people that choose to live in these locations should be willing to shoulder a fair portion of the costs in terms of property insurance — not exorbitant rates, but ones which truly reflect the risk of living in a vulnerable region. In addition, efforts to educate the public on effective preparedness needs to continue. Helping other nations in their mitigation efforts can also result in saving countless lives.
Finally, we need to continue in our efforts to better understand and observe hurricanes in order to more accurately predict their development, intensification, and track. References: Simpson, R. New York Acad. Frank, M. Corrin, C. Woodcock, A. Blanchard, C. Blanchard, D. NY Acad. Apart from the fact that this might not even alter the storm, this approach neglects the problem that the released radioactive fallout would fairly quickly move with the tradewinds to affect land areas and cause devastating environmental problems.
Needless to say, this is not a good idea. Now for a more rigorous scientific explanation of why this would not be an effective hurricane modification technique. The main difficulty with using explosives to modify hurricanes is the amount of energy required. The heat release is equivalent to a megaton nuclear bomb exploding every 20 minutes. In addition, an explosive, even a nuclear explosive, produces a shock wave, or pulse of high pressure, that propagates away from the site of the explosion somewhat faster than the speed of sound.
For normal atmospheric pressure, there are about ten metric tons kilograms per ton of air bearing down on each square meter of surface. In the strongest hurricanes there are nine. To change a Category 5 hurricane into a Category 2 hurricane you would have to add about a half ton of air for each square meter inside the eye, or a total of a bit more than half a billion ,, tons for a 20 km radius eye.
Hygroscopic refers to a substance that binds preferentially with water vapor molecules. Anyone who has used a salt shaker on a humid summer day understands- the salt clumps.
The barrier to this method is the assumptions and uncertainties in such a project that would require extensive testing first. Some people have proposed seeding the inflow layer of a hurricane with granules of some hygroscopic substance. The hope is that these granules will help form tiny cloud droplets, many more than would form naturally. There are several assumptions made in this chain of logic.
The first is that there are too few cloud condensation nuclei CCN available naturally. And lastly, it assumes that the increased burden on the updraft outweighs the increase in latent heat released when more liquid water reaches the freezing level.
If less water is precipitating out, then more will be freezing. Otherwise, you would expend a great deal of money and effort, but not change a hurricane sufficiently. It has been proposed to drop large amounts of the substance into the clouds of a hurricane to dissipate some of the clouds thus helping to weaken or destroy the hurricane.
The argument was that the glop would make raindrops lumpy i. The foregoing effect is larger than anything one could hope to produce in the real atmosphere. Did they watch any unmodified clouds? Isolated Florida cumuli have short lifetimes, and these are just the ones an experimenter would logically pick. Accepting for the sake of argument that they actually did have an effect, the descriptions seem more consistent with an increase in hydrometeor fall speed and accelerated collision coalescence, which the numerical model results argue would strengthen the hurricane, but not much.
One of the biggest problems is, however, that it would take a lot of the stuff to even hope to have an impact. A C-5A heavy-lift transport airplane can carry a ton payload. So that treating the eyewall would require sorties. A typical average reflectivity in the eyewall is about 40 dB Z , which works out to 1. If you crank the reflectivity up to 43 dB Z you need to do it every hour. If the eyewall is only 10 km thick, you can get by with sorties every hour-and-a-half at the lower reflectivity.
It was hypothesized to absorb sunlight and transfer heat such as black carbon, but it has not been carried out in real life.
Additionally, it would likely have negative environmental and ecological consequences, and if added in the wrong place, it could even intensify the storm. The idea here is to spread a layer of sunlight absorbing or reflecting particles such as micro-encapsulated soot, carbon black, or tiny reflectors at high altitude around a hurricane.
This would prevent solar radiation from reaching the surface and cooling it, while at the same time increase the temperature of the upper atmosphere. Being vertically oriented, tropical cyclones are driven by energy differences between the lower and upper layer of the troposphere. Reducing this difference should reduce the forces behind hurricane winds. It would take a tremendous amount of whichever substance you choose to alter the energy balance over a wide swath of the ocean in order to have an impact on a hurricane.
Knowing where to place it would also be tricky. These proposals would require a great deal of precisely-timed, coordinated activity to spread the layer, while running the risk of doing more harm than good. Many computer simulations should be run before any field test were tried. There has been some experimental work in trying to develop a liquid that when placed over the ocean surface would prevent evaporation from occurring.
If this worked in the tropical cyclone environment, it would probably have a limiting effect on the intensity of the storm as it needs huge amounts of oceanic evaporation to continue to maintain its intensity Simpson and Simpson However, finding a substance that would be able to stay together in the rough seas of a tropical cyclone proved to be the downfall of this idea. There was also suggested about 20 years ago Gray et al. The idea was that one could burn a large quantity of a heavy petroleum to produce vast numbers of carbon black particles that would be released on the edges of the tropical cyclone in the boundary layer.
These carbon black aerosols would produce a tremendous heat source simply by absorbing the solar radiation and transferring the heat directly to the atmosphere. This suggestion has never been carried out in real-life. Oil slicks are patchy, and likely would not cover a big enough area to affect the hurricane. It is also difficult to predict and control how and where the oil will move when affected by the storm.
If oil happens to spill and there is a storm, the oil could be carried into or away from the coastline depending on its track, but generally the storm will have a dispersing effect.
The largest impediment to this has to do with the energy expression of the hurricane. Even though a hurricane has huge amounts of energy, it is spread over a massively large area. In essence you would need wind turbine fields dozens of miles wide could both be anchored to receive the energy and mobile to follow the storms. Those systems would also need to withstand windblown debris and transmit the energy.
There have been proposals to tow icebergs to the Atlantic and cool sea surface temperatures, or to pump deep water to the surface. The problem with this is both the size scale and the movement of the hurricane, not to mention the track uncertainty and ecological implications.
Since hurricanes draw their energy from warm ocean water, some proposals have been put forward to tow icebergs from the arctic zones to the tropics to cool the sea surface temperatures. Others have suggested pumping cold bottom water in pipes to the surface, or releasing bags of cold freshwater from near the bottom to do this. Consider the scale of what we are talking about. The critical region in the hurricane for energy transfer would be under or near the eyewall region. If the eyewall was thirty miles 48 kilometer in diameter, that means an area of nearly square miles square kilometers.
Now add in the uncertainty in the track, which is currently miles km at 24 hours and you have to increase your cool patch by 24, sq mi 38, sq km. For the iceberg towing method you would have to increase your lead time even more and hence the uncertainty and area cooled or risk your fleet of tugboats getting caught by the storm. Just for the US mainland from Cape Hatteras to Brownsville would mean covering , sq mi , sq km of ocean floor with devices.
Lastly, consider the creatures of the sea. If you suddenly cool the surface layer of the ocean and even turn it temporarily fresh , you would alter the ecology of that area and probably kill most of the sea life contained therein. A hurricane would be devastating enough on them without our adding to the mayhem.
Seeding clouds, towing icebergs, and blowing up hurricanes with nukes all fail to appreciate the size and power of a tropical cyclone. When Andrew hit in , the eye and eyewall devastated a swath 20 miles wide.
The heat energy released there was 5, times the combined heat and electrical power generation of the Turkey Point nuclear power plant over which the eye had passed. Attacking every tropical disturbance that comes our way is not an efficient use of time either, since only 5 out of 80 become hurricanes in a given year. The best way to minimize the damage of hurricanes is to learn to co-exist with them.
Proper building codes and understanding the assumption of risk by choosing to live in a hurricane-prone area can help people evaluate their situation. Smart hurricane prep and public education, along with improved forecasting can help when a hurricane inevitably makes landfall. In the Atlantic basin Atlantic Ocean, Gulf of Mexico, and Caribbean Sea and in the eastern and central Pacific, as required, hurricane reconnaissance is carried out by two government agencies, the U.
Navy stopped flying hurricanes in Specifically, they show the number of hurricanes yellow area , and combined named storms and hurricanes red area that occur on each calendar day over a year period. The data have been smoothed using a 5-day running average centered on each calendar day. For the Atlantic basin the Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico , the chart is based on data from the year period from to starting at the beginning of the aircraft reconnaissance era but normalized to years.
The official hurricane season for the Atlantic basin is from June 1 to November 30, but tropical cyclone activity sometimes occurs before and after these dates, respectively. The peak of the Atlantic hurricane season is September 10, with most activity occurring between mid-August and mid-October. For the eastern Pacific basin, the analyses are based on data from the year period from to starting when there was reliable satellite imagery but also normalized to years.
The official hurricane season for the eastern Pacific basin is from May 15 to November 30, but tropical cyclones occasionally occur before and after these dates, respectively. A peak in activity is noted in late August, but this peak is less pronounced than the peak in Atlantic activity.
Relatively high levels of activity in the eastern Pacific tend to be spread out over a longer portion of the season than in the Atlantic, with most tropical cyclones occurring between late June and early October.
The figures below show the points of tropical cyclone genesis by day periods during the hurricane season. These figures depict named storms only. These maps show where tropical cyclones named storms and hurricanes tend to occur during each month of the hurricane season.
The data are shown as the number of named storms or hurricanes whose centers pass within nautical miles of a point on the map during a year period. For the Atlantic basin, the analyses are based on data from the year period from to starting at the beginning of the aircraft reconnaissance era but normalized to years. For the eastern and central Pacific basins, the analyses are based on data from the year period from to starting when there was reliable satellite imagery but also normalized to years.
Please note that the map legends vary from basin to basin and between named storms and hurricanes but not between months in order to make climatological patterns more apparent. Bars depict number of named systems yellow , hurricanes red , and category 3 or greater purple , Download hires image Download table of data PDF. It is issued when winds have reached, or are expected to reach within 12 hours, a speed marginally less than that which is considered gale force, usually mph.
Check for injured or trapped people, without putting yourself in danger. Watch out for flooding which can happen after a hurricane. Do not attempt to drive in flooding water.
Stay away from standing water. It may be electrically charged from underground or downed power lines. Evacuation Tips: Here is a list of tips on what you should do, if you chose to evacuate as a hurricane approaches. The second climate pattern is the Atlantic Multidecadal Oscillation AMO , which is, as the name implies, a trend that lasts anywhere from 25 to 40 years and is associated with warmer waters in the Atlantic and stronger African monsoons, Bell said. A warm-phase AMO conducive to hurricanes prevailed between and and since , Bell said.
Officially, the Atlantic hurricane season starts on June 1 and runs until Nov. However, most of these storms hit during peak hurricane season between August and October, on both coasts, according to the National Weather Service's Climate Prediction Center. Following in the footsteps of the record-breaking hurricane season of , this year is expected to pack a punch, with above-average activity forecast by the National Oceanic and Atmospheric Administration NOAA.
To make their predictions, scientists analyze a host of factors, from wind speed to sea-surface temperatures. The Climate Prediction Center classifies hurricane seasons as above-normal between 12 and 28 tropical storms and between seven and 15 hurricanes ; near-normal Between 10 and 15 tropical storms and between four and nine hurricanes and below-normal Between four and nine tropical storms and two to four hurricanes.
On average, the world is seeing stronger tropical cyclones a term that encompasses fast-rotating storms such as hurricanes and typhoons more often than in decades past. According to an analysis of 4, tropical cyclones from to , researchers concluded in that due to global warming these storms are not only getting stronger , but we are experiencing the strongest of the pack more frequently, Live Science reported. In another study, scientists discovered that compared with six decades ago, hurricanes that blast Bermuda are twice as strong, they reported online Feb.
We can thank climate change for another hurricane downer: Global warming is leading to so-called zombie storms, or those that peter out and then get refueled to sort of rise from the dead, Live Science reported.
For instance, in September , the Category 1 hurricane Paulette made landfall in Bermuda, strengthened into a Category 2 and then weakened and died out some 5. And according to scientists, such zombie storms could become more frequent, as waters warm up and give once-dead storms new life, according to Live Science.
According to HurricaneCity , a hurricane-tracking website, here are the top 10 cities most frequently hit or affected by hurricanes since record-keeping began in At that point, scientists use a 1 to 5 scale known as the Saffir-Simpson Hurricane Wind Scale to classify hurricane strength , with category 1 being the least severe hurricanes and category 5 being the strongest. Some scientists have also proposed adding a category 6 to account for storms that are well beyond the highest sustained wind speed for a category 5 hurricane.
Some scientists have argued against using just wind speed as a metric to determine a storm's severity and potential damage, arguing that other metrics such as storm surge height or rainfall could provide better insight into a storm's ferocity. However, the National Hurricane Center NHC has argued that metrics like storm surges can be hard to predict because local differences in the shape of the terrain of the ocean floor leading up to the coastline can determine the height of storm surges.
Hurricanes initially were named in honor of the feast day for a Catholic saint. For instance, Hurricane San Felipe occurred on Sept. Hurricanes that struck on the same day would be distinguished by a suffix placed on the later one, Live Science previously reported. For example, a storm that struck on Sept.
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