The Greatest Storm on Earth:Whurricane

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TITLE The Greatest Storm on Earth:wHurricane. INSTITUTION National Oceanic and Atmospheric Administration (DOC), Rockville, Md. REPORT NO NOAA/PA-76008 77 PUB DATE -, NOTE 48p.; Photographs may not reproduce well AVAILABLE FROM Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (no price quoted)

EDRS PRICE 'MF-$0.83 HC-$2.06 Plus Postage. DESCRIPTORS Bibliographies; *Climatic Factors; Earth Science; Economic Factors; Environmental Influences; *Ins4ructional Materials; *Meteorology; Natural Sciences; Science Education; *Secondary School Science; Social Factors IDENTIFIERS *Hurricanes

ABSTRACT . This publication, produced by the National. Oceanic and Atmospheric Administration (NOAA), is an illustrated non-technical description of'the meteorology of hurricanes and their effects on the land areas they hit. As an information source for students aid teachers alike, this publication also describes the damage done in the past by hurricanes, the atmospheric processes behind hurricanes, and the efforts of forecasters and hurricane hunters; A bibliography is also included. (MR)

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eonfcn Hurncanes manifest their brute strength in many ways. At left. the land and sea beneath a passing hurricane. At ;.,,krft§Grepe..st.Storm onEarth 1 The Fatal Thrust Toward Land 12 nght, a NOAA satellite image of ... 2 -11/e.struction in a Hurricane 14 . ttiOtaitift of Great Storms hurncane Ava, the classically organized A -4 Forecasters and Huntee' 16 Atmospheric Selena mte 1973 storm that isstill the most violent A Storm is Born 8 Stormfury 18 hurricane of record for the eastern north Portrait of a Hurricane 10 Hurricane Bibliogiaphy 21 Pacific area.

5 4 There is nothing like them in the two theusp-id more perished on the atmosphere. Even seen by sensors Gulf Coage of Louisiana. The Galves, on spacecraft thousands of miles ton storm o'f- ipoo took more than abOlie the earth, the uniqueness of six thousand livese than 1,800 these powerful, tightly coiled storms perished along the Vuth shore of is clear. They are not the largest Florida's Lake Okeechobee in 1928 storm systems in our atmosphere, or when hurricane -driven waters the most violent; but they combine broached an earthen levee. Cuba lost those qualities as no other phenorn. more than two thousand to a storm enon does, as if they were designed in 1932. Four hundred died in Flori- to be engines of death and da in an intense hurricane in destruction. September 1935the "Labor Day" In our hemisphere, they are hurricane that shares with 1969's called hurricanes, a term which Camille the distinction of being the echoes colonial Spanish and Carib- most severe of record. beanIndian words for evil spirits and Floods from 1974's hurricane big winds. The storms are product!. Fifi caused one of the Western of the tropical ocean and atmos Hemisphere's worst natural disasters phere, powered by heat from the in history, with an estimated five sea, steered by the easterly trades thousand persons dead in Honduras, and temperate westerlies, and their and thousands more in Nicaragua, own fierce energy. Around their tran- El Salvador, Guatemala, and Belize. quil core, ..'nds blow with lethal In the United States, the hurri- velocity, the ocean develops an inun- cane death toll has been greatly 4 dating surge, and, as they move diminished by timely warnings of ap- ashore, tornadoes may descend from-proaching storms. But damage to the advancing banns of thunder.'` fixed property contipties t8 mount. clouds Camille, in 1969, caused some' $1.42 Hyrricanes have a single belie. billion in property damage. Foods an "1: fitthey are a major source of rain fromAgnesin1972cost for th,ose continental corners which estimated $2.1 billion. fall ,beneath their tracks. Perhaps , That is why such first -order there are other hidden benefits as technical accomplishments as early well. But the main consequence of detection and timely warning of ap- the hurricane is tragedy. proaching hurricanes are not enough In Asia, the price in life paid for sorrk! scientists. For them, there the hurricane has had Biblical pro- is the persistent goal of somehow portions. late as 1970, cyclone disarming the greatest storm on storm tide's- along the coast of what earth. is now Bangladesh killed hundreds In the United States, hurricine of thousands of persons. warning and research are focused in Our hemisphere has not had NOAH, the National Oceanic and At. such spectacular losses, but the toll mosphenc Administration of the has still been tragically high. In U.S. Department of Commerce. Ancl August 1893, a great storm wave there, as the planet orbits toward drowned more than a thousand the summer solstice, scientists, people in Charleston, South Carolina.technicians, pilots, and others brace In October of that same year, nearly for another season of great storms.

1 the season of great storms

Cumulus clouds, the atmosphere's basic weather -factories,- and building blocks for hurricanes, climb high into the o atmosphereunder the energetic influence of the tropical sun. 9 Itis the northern summer. The illU co_lc. Again after mid.September, sion of a moving sun caused by our most storms begin in the western planet's yearlong orbit brings that Caribbean and Gulf of Mexico. star's direct rays northward to the In an average year, moreZhan Equator, then toward the Tropic of one hurJred disturbances with hur Cancer. Behind this illusory solar _ ricane potential are observed in track the sea and air grow warmer, the Atlantic, Gulf, and Caribbean; but and the polar air of winter beats feftrer than ten of these reach the its seasonal retreat. tropical storm stage, and only this northward shift of the sun about six mature into hurricanes On brings the season of tropical cy- average, three of these hurricanes clOnes to the Northern Hemisphere. strike the United States, where Along ow. coasts and those of Asia they kill'from about 50'tp. 100 it is time to look seaward. / people somewhere between Texas Over the western Pacific, the and Maine anL4 Cause hundreds of tropical cyclone season is never quite millions of dollars' property damage 11,11, over, but varies greatly in intensity In a worse than rage year, the Every year, conditions east of the same storms cause several hun- Phillippines send a score of dred deaths, and property damage violent storms howling toward Asia: totaling billions o. dollars; but it is worst from JJne For NOAA, the hurricane season through October. means another hazard from the at Southwest of Mexico, eastern rnophere, at a time when Pacific hurricanes develop tornadoes, and floods, and severe during spring and summer. Most of storms are playing havoc elsewhere these will die at sea as they move on the continent. Meteorologists over colder ocean waters. But with NOAA's National Weather Serv- there are destructive exceptions when ice monitor the massive flow of storms curve back toward Mexico. data that might contain the early Alorig our Atlantic and Gulf indications of a developing stornr , coasts, the nominal hurricane season somewhere over the warm sea lasts from June through cloud images from satellites, meteor- await per ye. . yea& per yor ak ewe p. IkeIM, per year IartlIZt le7 9 TROPICAL 80 TROPICU TROPICAL CYCLONES TROPICAL CYCLONES 280 T ICAL November. Early in this season, the ological data from hundreds of CYCLONES CYCLONES BAY OF BENGAL 80 EAST COAST CYCL S western Caribbean and Gulf of surface stations and balloon M 31 HURRICANES et, 48 HURRICANES ARABIAN SEA 15 AUSTRALIA 31 Aa zo4 T NS MADAGASCAR TO WEST COAST Mexico are the principal areas of ori- probes of the atmosphere, 90E 51 AUSTRALIA 2I gin. In July and August, this information from hurricane - hunting center begins an eastward shift; by a:rcraft. early September a few storms are In NOAA's Environmental being born as far, east as the Research Laboratones, scientists wait. Cape Verde Islands off Africa's west for nat,,re to furnish additional sped. mens of the great storms to probe, analyzeeventually to modify, if they can be modified with ri beneficial results.

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Over the Atlantic, the budding cooling with altitude, cools only to The Polar Trough. When the vertical circulation accelerates, and a summer brings other changes as the inversion altitude, then grry..s Bermuda High is weak and south of vortex develops that sometimes well. A sernipe,rmanent zone of warmer, before it begins to cc il its normal position, and the easterly reaches hurricane intensities. high pressurethe familiar "High" of aaarn at greater heights. Beneath the trades are shallow (below about Easterly waves aie present over weather mapsreturns to a surface inversion layerair sweeps for hun- 15,000 feet, or 4,500 meters), some part of the Caribbean almost position centered near Bermuda dreds of miles over the surface an elongated area of low pressure daily ' -m June through Septem- and the Azores. This clockwise spiral of the sea, receiving a charge of a troughembedded in the be- ,e months of highest incidence of descending air, or anticyclone, moisture to altitudes of several thou- temperate westerlies may push of ril-icanes. The waves are also lies between the temperate and sand feet from evaporated ocean southward into the tropics. When t' pre, ) a lesser extent in May, tropical bands of prevailing winds, water. southern end of the intruding October, and November. and, during summer and early Convection, or vertical motion, in trough slows its eastward move- autumn, dominates the North this lower, heated layer, and inter- ment, or is trapped in the easterly Migrants from the Doldrums.The Atlantic atmosphere. mittent intrusions of moist air, trades, a hurricane may develop: tropical easterly tradewind belt of North of the high-pressure weaken the inversion, which gracLially or the trough may separate to be- the Northern Hemisphere has a system, prevailing westerlies flow dissipates as the low-level air come another weather-makerthe mirror image in a similar belt of eastward in a deep layer extending continues its trajectory above the easterly wave. winds south of the Equator. A high. from the surface to altitudes of warm sea. This vertical penetration of ly simplified view of the 40,000 feet (12,000 meters) or more. the inversion permits water vapor The Easterly Wave. Once ern atmosphere would show these trade- Near the center of the Bermuda to be lifted to Look; altitudes, bedded in the deep easterly current, wind belts separated by an equatorial High, winds are variable. But to the where it condenses into clouds and this westward-drifting region of region of low pressure, popularly south, the surface flow of air is pre- raindrops. As water vapor con- low-pressure tends to organize low- called the doldrumswhat meteor dominantly to the west the denses, it releases heat energy into level circulation into alternate areas ologists call the Intertropical easterly tradewinds. In the northern the atmosphere. This latent heat of converging and diverging airflow. Convergence Zone, or ITCZ.' summer, these easterlies may energy is gradually transported to Where air is diverging (high The ITCZ varies considerably deepen until they reach from the higher levels, changing the vertical pressure), weather is fine. But where more than this simple view indicates surface to the stratosphere, and cov- character to the tradewind belt. convergence occurs (low pressure), Sometimes it is sc weak as to be er vast areas of the tropics; or Sometimes the easterly flow is suf- the depth of the moist laye: in they may break up into small ficiently disturbed by such processes creases, and convection produces vortices (a whirlpool is a vortex) that rain areas become concen heavy cumulus and cumulonimbus which drift wvstward into the Carib trated, and the concentration clouds which build to heights6above bean or Gulf of Mexico. It is in this intensifies into a storm. 30,000 feet (9,000 meters). tradewind current that most Atlantic Many of the waves in the hurricanes are born. easterlies have been traced back to The characteristic sinking of air western Africa, where they are most within the anticyclone produces evident in the middle and low layers in the deep current of the levels of the atmosphere as they easterly trades. As air sinks to If:vels cross Africa's Atlantic coast. These of greater atmospheric pressure, it systems may travel thousands of is heated by compression, miles with little change in form. But producing at lower altitudes what is where the waves are destabilized called a temperature inversiona by intense convection or by so.ne condition in which air, instead of external forcefor example, high. level winds that promote greater organization of the circulation in the wavethey may curl inward. The

5 14 15 I OCT I DEC JAN 1 SEP FEB1 MAR 1APR I MAY JUN JUL AUG NOV

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nearly undetectable, and almost In February the ITCZ moves from a southern range of its annual migra hurricanes of the eastem North Paci- completely free of significant weath- position near the Equator to its tion (it'is never south of the fic, and similar storms like the er. At other times it can be an extreme limit near about twelve Equator) the effect of the earth's ro cyclones of the Indian Ocean, and intensely active zone a hundred miles degrees north latitude in August; tation is small; but a., it shifts the western Pacific's typhoon. or more wide, with cloud tops however, its day-to-day surface northward, the influence of the ro- The storms tend to be bom over rising to the stratosphere and position varies greatly. tating globethe Coriolis force is warm water, spun from disturbances weather, as violent as that in the This interhemispheric borderland great enough to permit a circulation in the equatorial tradewind belts continental squall lines which sweep has a flow consisting mainly of to develop that can evolve into the There is little tropical cyclone activity our own great plainS. eddies (individual currents in a mov- tight, violent eddy of a tropical south of the equator, except for The ITCZ also follows the sun. ing fluid) that drift westward, and cy )ne. the ocean area west of Australia dur- its intense activity is thought to be ing the southern summer. associated with the movement of Hurricanes in Other Oceans.What these ed 'es into the tropics. is true for hurricanes in the North While the ITCZ is in the Atlantic is generally true for the 6 1 7 16 111111=1111t

AZORES BERMUDA HIGH

The characteristic vertical structure of the east B. erly trade wind belt, in MEd a relatively shallow C. layer cd moist airis overlain by a deeper layer of Intensified convection may be accompamed by a As the inversion layer weakens to the west and subsidi,s2 wym dry air1' e two layers are separated trough of low pressure in the trade wind beltThis as the lower layers become increasingly warm and Clouds form, and by a temperature'inver_lon Moisture from the poorly developed easterly wave is weak atthe moistconvection intensifies Increased cc.rivection, and the pumping action of evaporates into the lower atmosphere but can saface stronger nea' 15 009 feet weak at high begin to rise to greater altitudes high altiiude winds. may cause the easterly v,,,e not rise above the inversion However the moisture altitudeThurdrstorms may develop behind the to deepen furtherbecoming strong from the sur charge received by the lower layers contains the Atmospheric pressure Nave as the airis raised and shunted northward, face to 15 000 feet or incie latent heat energy that once released by ccndensa ahead of the waveairis subsidingweatheris atthe surface dropsan area of ;OM pressure tion and convection to high levelscan drive a becomes an isolated dopresqon aid the trade fine A wave ofthisintensity may travelfor tropical disturbance winds beg n to turn in on themselvesforming a thousands of miles without 4, eciable change weak cyclonic miculation abut the cente, of low pressureThis circulatioo may intensify, pressure may continue to dror, the winds spiralling around the cuter of low pressure may accelerate disturbance may become a severe tropical cyclone

PRESSURE INCREASING

4111MINCEMUM1111111111i1M11=M111011 13 19 ,, a storm is born

Birth of hurricane Carmen in August 1974 is watched by sensors aboard a Synchronous Meteorological Satellite, in an orbit that keeps it always about 22,000 miles (33,000 kilometers) over the same point on the equator The embryonic Carmen begins as a poorly organized disturbance in the easterly wave (1), Then seems to weaken (2) as the young storm crosses a persistent upperlevel trough. But Carmen survives to become a tropical storm headed for the Antilles (3), and a fullscale hurri cane (4) that stnkes into Yucatan. Colored cir, -s are centered on the storm's approx imte center of rotation.

21 As the disturbance becomes bet_ organized and more intense, the familiar shape of the humcane appears At matunty, the storm is nounshed by air converging at lower levels in a great spiral toward the center of low pressure, where convection (vertical motion) and the pumping actirn of high-altitude winds thrust it upward into a larger, anticyclonic circulation. Vertical scale is greatly exaggerated.

hausted at -high altitudes. This pumping actionand the heat released by the ascending, water- bearing airexplains the sudden drop in atmospheric pressure at the HIGH ALTITUDE WINDS surface. The drop produces the hurricane's uniquely steep pressure gradient, along whose contours winds are accelerated to hurricane Hurricane formation was once with an infinitude of unknowns. (in the Northern Hemisphere) speeds. believed to be something like There is no full understanding of the movement of low- and mid- It is generally believed that the generation of thunderstorms, what triggers a hurricane, or how a level air is counter-clockwise. Now the interaction of low-level where surface heating causes air to disturbance in the easterly trades the storm is an embryo and high-altitude wind systems at rise, water vapor to condense, and or a disturbance along the ITCZ is hurricane. scales larger than the hurricane's thunderclouds to grow. But, in hur- transformed into a mature storm. High-altitude winds help the determines the intensity the ricanes, there was an additional This is what seems to happen. developing hurricane's massive storm will attain. Scientists also be- dementthe inexplicable drop in at- Some starter mechanismthe in- vertical transport exhaust air into lieve planetary wind systems, mospheric pressure that organized truding polar trough, easterly the upper reaches of the tropo- displaced northward, set up an es- these elements and spun them wave an eddy from an active ITCZ sphere, the lower level of the sential large-scale flow which into a cyclonic spiral. stimulates an area of vertical atmosphere where most vertical supports the budding storm, and This theory left much to be air motion. The initial disturbance mixing and weather occur. These that the development of hurricanes desired. Few hurricanes mature in creates a region into which low- winds pump ascending air out is often preceded by high-level the doldrums, where this kind of level air from the surrounding area of the cyclonic system into the warming and low-ievel inflow, in activity is usually found, and there begins to flow, accelerating the clockwise circulation of a high- some balance that is not fully are too many seemingly ideal convection already occurring altitude anticyclone, carrying air understood. There is still much to convective situations there and too inside the disturbance. As water va- well away from the disturbe learned. For example, re- few hurncanes. And what of the por in the ascending moist bance before it can sink to the searchers have begun to ponder drop in atmospheric pressure? columns condenses (releasing surface again. the connection between thun- Even storms as neatly large amounts of heat energy to Thus, a large-scale vertical derclouds over the hotplate of constructed and carefully observed drive the wind system), the vertical circulation is set up in which low- Central Afri '-a and disturbances in as hurricanes present scientists circulation acquires greater level air spirals up the cyclonic core the easterly Eradewind belt, and organization; and the horizontal of the disturbance, and is ex- how these are affected by the form of the disturbance becomes massive natural cloud seeding of the familiar cyclonic spiral, in which Saharan dust. 22 23 Given that the hurricane, as an Makimum winds run still higher in engine, is inefficient and hard to start typhoons. and sustain, once set in motion, Hurricane winds are produced, port once mature, itis an awesome as all winds are, bydiffe;ences in natural event indeed. atmospheric pressure, or density. The The young storm stands upon pressure gradientthe rate of the'sea as a whirlwind of awful pressure change with distance4 ofa violence. Its hurricaneforce winds produced in hurricanes is the cover thousands of square' miles, sharpest in the atmosphere, and gale force windswinds of 33 excepting only the pressure hurricane to 55 knots* (16 to 28 meters per change believed to exist across they lecOnd),over areas ten times larger. narrow funnel of,a tornado. st ^4 Along the contours of its spiral run Atmosperic pressure is popularly bands of dense clouds from whiCh expressed as the height of a column torrential rains fall. Tt ese spiral of mercury that can be supporteckby rainbands ascend in decks of the weight of the overlying air at a cumulus and cumulonimbus clouds given time.** In North America, bar° to the high upper atmosphere, where metric measurements; at sea level condensing water vapor is swept off seldom go below 29 inches of 4 as ice crystal wisps of cirrus clouds mercury (982 millibars), and in the by highaltitude winds. Lightning tropics it is generally close to 30 glows in the rainbands, and this inches (1,016 millibars) under cloudy terrain is whipped by normal conditions. Hurricanes drop ottorbulence. the bottom out of those normal t In the lower few thousand feet, categories. The Labor Day hurricane air flows in toward the center of the that struck the Florida Keys in 1935 cyclone, and is whirled upward had a central pressure of only 26.35 through ascending columns of air inches (892 millibars). And the near the center. Above 40,000 feet change is swift: pressure may drop (12,000 meters), this cyclonic pattern an inch (33 millibars) an hour, with is replaced by an anticyclonic a pressure gradient change of a circulationthe high-level pump tenth of yn inch (3 millibars) per which is* the exhaust system of the mile. hurricane engine. At the center of the storm is a At lower levels, where the unique atmospheric entity, and a hurricane is most intense, winds on persistent metaphor for order in the the rim of the storm follow a wide midst of chaosthe eye of the pattern, like the slower currents on hurricane. It is encountered suddenly. the rim of a whirlpool; like those From the heated tower of maximum. currents,, these winds accelerate as winds and thunderclouds, one bursts they appioach the central vortex. into the eye, where winds diminish to This inner band is the eyewall, where the storm's worst,winds are felt, and 'A knot is one nautical mile per hour, a

where moist air entenng at the nautical mile is about 1 15 statute miles surface is chimneyed upward, "Weather maps show atmosphenC pressure releasing heat to drive the storm. In in millibarsunits equal to a thousandth of a bar. the bar is a unit of pressure equal to most hurricanes, these winds exceed 295.3 inches of mercury in the English 90 knots (50 meters per second) system, and to one million iiynes per square nearly twice that in extreme cases. centimeter in the metnc system 10 24 J O

.: .. something less than 15 knots (eight meters per second). Penetrating the .. opposite wall, one is abruptly in the --worst of winds again. .A mature hurricane orchestrates more than a million cub milesof atmosphere. Over the deep ocean, waves generated by hurricaneinds 4, can reach heights of 50 feet (15 meters) or more. der the storm center the ocean suce is drawn ''': upward like water in a giant straw, forming a mound a foot or so higher than'the surrounding, ocean surface. This mound translates int4 coastal surges of 20 feet (six

. meters) or more. Besides this surge, massive swells pulse otit through the upper layers of the seaPacific, surfers often rick he oceanic - memory .distant typhoons. Hurricane Eloise, which struck the Florida panRendle in September 1975, taught scientists something Srt new about the influence.of passing hurricanes on the marine environment. Expendable bathytherrnographs dropped from/ '. NOAA research aircraft ,ahead of, in, , and in the wake of the storm showed that the ocean was disturbe!., to depths of huncifedsnf feet by a t. passing . hurricane, and "remem- Portrait of a hurricane, as seen'by bered': hurricane passage with inter- satellite, radar, and illustrator. Cut- "; nal waves that persisted for weeks away view of storm is greatly exag- after the storm had gone. The same gerated in vertical dimension; actual storm also demonstrated that a hurricanes are less than 50,000 'set passing hurricane can b. felt deep in (15,000 kilometers) high and may the sea-floor sediments. cover a diameter,of several hundred While a hurricane lives, the miles. transaction of energy within its circulation is immense. The .. condensation heat energy released .'by a hurricane in one day can be the equivalent of energy released by fusion of four hundred 20-megaton hydrogen bombs. One day's released energy, converted to electricity, could supply the United States' electrical needs for about six months.

26 - 27 the fatal thrust toward land

Hurricane waves besiege a seawall as a storm makes landfall along our Atlantic coast. This thrust toward land is suicidal for the storm, which dies soon after it has extracted its toll in life and pro 'v where it comes ashore. 9 9 --

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Trends and exceptions in the great storms' thrusts toward land. Shaded areas show general patterns of westward drift and recurvature. Act Jai storm tracks describe a From birth, the hurricane lives in an As long as this easterly drift is Celsius) does not contribute much few of the countless variations possible environment that constantly tries to slowless than about 20 knots, or energy to a hurricanL. Even though 10 meters per second- -the young some large hurricanes may travel for kill itand ultimately succeeds The eastern United States, about a fourth hurricane tends to survive whale itis hurricane may intensify. More rapid days over cold North Atlantic water, forward motion generally inhibits in- all storms are doomed once they of the annual rainfall comes from over warm water. But its movement dissipating hurricanes, and the Asian is controlled by the forces which tensification in the storm's early leave the warm tropical waters which stages. Entering the trnperate sustain them. The farther they mainland and Japan suffer typhoons eventually destroy it, forces which to get water from the sky. drive the storm ashore or over latitudes some storms may move venture into higher latitudes, the less along at better than 50 knots (25 fuel they receive from the sea; this Hurricanes are cften resurrected colder water beyond the tropics into extratropical cyclones at nigher where it will fill and die. This thrust meters per second), but such :ast- lack of fuel finally kills the storms. moving storms soon weaken. Over land, hurricanes break up latitudes, or 'ombine with existing away from the tropics is the temperatezone disturbances. Many At middle latitudes. the end rapidly. Cut off froin their oceanic clockwise curve which takes storms moving up our Atlantic coast usually comes swiftly. Colder air source of energy, and with the typhoons across the coastlines of are in the throes of this transfor- Japan and into the Asian mainland, penetrates the cyclonic vortex, the added effects of frictional drag, their warm core cools, and acts as a circulation rapidly weakens and mation when they strike New and Atlantic hurricanes into the England, and large continental Lows eastern United States. thermal brake en further becomes more disorganized. intensification. Water below 80 Torrential hurricane rains, however, are often invigorated by the Even before a hurricane forms, remnants of storms born over the the embryonic storm has forward degrees Fahrenheit (27 degrees may continue even after the winds motion, generally driven by the east- are much diminished. In the south- tropical sea. erly flow in which it is embedded. 13 30 31 ifictiovr Az, I .1A ."1-

4r. destruction , . in hurricane

Wind and water do the humcane's destructive work. The mighty storm tide and powerful, debris.laden winds create .such scenes of havoc as these. 33 Hurricanes are the unstable,"unreli- . All the wind damage does not able creatures of a moment in our necessarily come from the hurricane. planet's natural history. But their brief As the storm moves shoreward, inter- life ashore can leave scars that never actions with other weather systems 'quite heal. In the mid1970's, the can produce tornadoes, which work hand of 1969's Camille could still be around the fringes of the hurricane. seen along the Mississippi Gulf Although hurricanespawned Coast. Most of a hurricane's tomadoes are not the most violent destructive work is done by the form of these whirlwinds, they have general rise in the height of the sea added to the toll we pay the called storm surge, wind, and flood- hurricane. producing rains. Floods from hurricane rainfall Hurricane winds can be the least are quite destructive. A typical hur- destructive of these, although there ricane brings 6 to 12 inches (150 are important exceptions like 1971's to 300 miilimeters) of rainfall to the Celia, whose high winds did most of area it crosses, and some have the storm's destructive work. These brought much more. The resulting t. , winds are a force to be reckoned floods have caused great damage with by coastal communities decid- and loss of life, especially in ing how strong their structures mountainous areas, where heavy should be.' For example, normal rains mean flash floods. The most atmospheric pressure at sea level is widespread flooding in United States about two thousand pounds per history (through 1976) was square foot (19,000 kilograms per caused by the remnants of square meter). As winds increase, hurricane Agnes in 1972. Rains from pressure against objects is added at the dying hurncane brought a disproportionate rate. Pressure disastrous floods to the entire At- mounts with the square of wind lantic tier of states, causing 118 velocity, so that a tenfold increase in deaths and some $2.1 billion in wind speed increases pressure one- property damage. hundred-fold. Thus, 20-knot (12 The hurricane's worst killer meter-per-second) wind increases comes from the sea, in the form of atmospheric pressure by about two storm surge, which claims nine of 4. pounds per square foot (10 every ten victims in a hurricane. coastline along the Atlantic and Gulf waves to severely erode beaches and coastal' highways. Many buildings kilograms per square meter); a wind As the storm crosses the coasts lies less than 10 feet (3 withstand hurricane winds until, their of 200 knots (110 meters per continental shelf and moves close to meters) above mean sea level, the foundations uncle- )fined by erosion. second) increases atmospheric pres- the coast, mean water level may danger from storm surges is great. they are weakeneu acid fail. Storm sure by more than 225 pounds per increase 15 feet (5 meters) or more. Wave and current action associ- tides, waves, and currents in con- square foot (1,100 kilograms per The advancing storm surge ated with the surge also causes fined harbors severely damage ships, square meter). For some structures, combines with the normal astro- extensive damage. Water weighs this added force is enough to cause nomical tide to create the hurricane some 1,700 pounds per cubic yard marinas, and pleasure boats. In estuarine and bayou areas, intrusions failure. Tall structures like radio storm tide. In addition, wind waves (1,000 kilograms per cubic meter); of alt water endanger the public towers can be worried to destruction five 10 feet high are superimposed extended pounding by frequent healthand create bizarre effects like by gusting hurricaneforce winds. on the storm tide. This buildup of waves can demolish any structures the saltcrazed snakes fleeing Lou- Winds also carry a barrage of debris water level can cause severe flooding not specifically designed to with- isiana's flooded bayous. that can be quite dangerous. in coastal areas, particularly when the stand such forces. storm surge coincides with normal Currents set up along the coast high tides. Because much of the by the gradient in storm surge United States' densely populated. heights and_wind combine with the 33 34 .orecaster and hunters

Stalking a storm (shown in the satellite photograph), rough nding meteorolr ists, may fly right to the hurricane's eye nor detailed information . 37 .._ The day is past when a hurricane Babe, Clara... that changes each or two of its predicted landfall, these could develop to maturity far out to year, and is different for the North advisories begin to carry hurricane sea and go unreported until its thrust Atlantic and the Eastern North watch and warning messages, telling toward land. Earth - orbiting satellites Pacific. Typhoons also receive names people when and where the ci operated by NOAA keep the earth's in alphabetical order. but beca,Ise hurricane is expected to stfike, and atmosphere under virtually they occur tnroughout the year, what its effects are likely to be. Not continuous surveillance, night and these storms are named cor.,utive- until the storm has decayed 'Dyer clay. Long before a storm has ly without regard to the ,ear `that is, land and its cloudy dements and evolved even to the pdint of ruf- a calendar year of typhoon activity great cargo of moisture have fling the easterly wave, scientists at could begin with typhoon Wanda. blended with other brands of NOAA's National Hurricane Center* The first hurricane warning in weather, does the hurricane (a National Weather Service Forecast the United States was flashed in .emergency end. Office) in Miami, Florida, have begun 1873, when the Signal Cr )s warned This system works Well. The to watch the disturbance. In the against a storm approach' g the death toll in the United States from satellite data coming in from polar- coast between Cape May, New hurricanes has dropped steadily as orbiting and geostationary spacecraft, Jersey, and New London, Connect NOAA's hurricane tracking and and in reports from ships and cut. Today, naming a storyis a warning apparatus has matured. Al- aircraft, they look for subtle clues signal which brings a considerably though the accuracy of hurricane that mark the development of hur- more elaborate warning system to forecasts has improved over the ricanescumulus clouds covered by readiness. Long distance communica- years any significant improvements the cirrostratus deck of a highly or- tions lines and preparedness plans must come from quantum jumps in ganized convective system; showers are flexed. scientific understanding. that become steady rains; dropping As an Atlantic hurricane drifts The forecasters also know that atmospheric pressure; intensification closer to land, it comes under science will never provide a full solu- of the tradewinds, or a westerly wind surveillance by weather reconnais- tion to the problems of hurricane component there. sance aircraft of the U.S. Air Force, safety. The rapid development of Then, if this hint of a the famous "Hurricane Hunters," who America's coastal areas has placed disturbance blooms into a tropical bump through the turbulent interiors millions of people with little or no inorm, a time.honoyed convention is of the storms to obtain precise fixes hurricane experience in the path of /applied: it receives a name. This on the position of the eye, and these lethal storms. For this ipractice began in the 1940's, when measure winds and pressure fields. vulnerable coastal population, the wartirne weathermen plotted the Despite the advent of satellites, the answer must h.- community movement of stormsinformally aircraft probes are the most detailed preparedness and public education in named for wives and sweethearts information hurricane forecasters the hope that education and across vast theaters of operationsIt receive. The hurricanes are also planning before the fact will save has been Weather Service policy probed by "flying laboratories" from lives and lessen the impact of the NOAA's Research Facilities Center in hurricane. since 1953. The system uses an '"? alphabetical series of names -- Anita, Miami. Finally, the approaching storm comes within range of a radar network stretching from Browns- ville to Boston, and from Miami to More tropical cyclone advisones are issued by the Lesser Antilles. NOAA's Humcane Warning Offices in Honolulu and San Francisco than by Morn Through the lifetime of the These Weather Service Offices keep the same hurricane, advisories from the kind of watch for the same destructive storms, National Hurricane Center and other and warning is given to ships and coastlines waming offices, give the storm's' in their path. But. because the Pacific position and what the foretaste-, in tradewinds carry most storms away from land, this warning work is perhaps best known to Miami expect the storm to do. As aviators and manners the hurricane drifts to within a day 38

i.. kinfeMiraosart4i i". .madam*

NOAA's VVP3D Orion flies a hug ,ane mission dunng Project Stormfury, an effort to determine whether man can modify humcanes through cloud seeding with beneficial results C 40 No human effort to change the and adjacent spiral bang., causing Stormfury has been chronically Hurricane Debbie was the first atmosphere has quite the dimensions supercooled waterwater cooled short on experimental opportunities, storm subjected to multiple seedings of Project Stormfury, NOAA's ex- below freezing but still in liquid however. Public concern that seeding (August 18 and 20, 1969), receiving perimental attempt to mitigate the formto freeze, releasing large might cause a storm to change its massive charges of silver iodide at winds of hurricanes. As a scientific quantities of heat enemy into the track, or increase intensity after two-hour intervals, five times each achievement, learning to modify hur- clouds near the eye. inis large seeding, or reduce seasonal rainfall day. Appreciable changes in ricanes would rate very high. As a release of latent heat of fusion out- from hurricanes, or simply "go maximum wind speeda 30-percent complex, carefully executed field side the ring of maximum winds, the against nature," has partly shaped reduction on the 18th, 15 percent on experiment, in the atmosphere, it has hypothesis went, would flatten the the experiment; but recent research the 20thand other parameters few equals. ' pres-iire gradient, causing the and past observations indicate such related to the structure of Debbie Stormfury is an effort to learn hurricane to spread into a storm fears are groundless. Scientific occurred after seeding. Analyses of enough abnut hurricanes to be able system of lesser intensity. concern that the hurricane be past storms indicated the rate of to say whether they c'an be altered Today, the Stormfury hypothesis handled objectivelythat is, decrease in wind speed observed on through cloud seeding, with benefi- has been refined by measurements seeded and monitored over the August 18 would be very rare in an cial results. The experiment brought back by new airborne neutral environment of the ocean unseeded hurricane; and windspeed developed from studies performed sensors, and analysis in the Miami has also been a powerful shaping decreases on August 20 could be since 1956 by what is now NOAA's laboratory. The present seeding stra- fornc. These factors led to stringent expected to occur naturally in few- National Hurricane and Experimental tegy is to seed clouds outside the rui2s which prohibit seeding when er than or e tenth of a sample of Meteorology Laboratory, in Miami. eyewall, in an effort to redistribute the storm has more than a ten unmodifiei storms. The fact that the Basically a kind of atmospheric judo, the mass flow of the storm. Here, percent chance of making landfall storm's wind diminished on both it pits scientists and aircraft and seeding still converts supercooled within 24 hoursconstraints which seeding days suggests the cloud-seeding techniques against the water to ice, triggering the release of have put many storms out of modification experiments were giant forces of a hurricane. The enormous quantities of energy into reach. effective. object is to use the giant's own the storm outside the eyewall. But From 1961 through 1971, Results obtained from hu-ricane energy against it, setting in motion the effect is to cause immature Stormfury, then a joint Department Ginger, seeded on Septembe, 25 rearrions within the storm that finally clouds there to develop, condensing of Commerce-Department of Defense and 28, 1971, were ambiguous The red..2its intensity, more water vapor at greater experiment, was able to "treat" only silver iodide seeding agent was The rationale for Stormfury is distances from the eye, the heat of four storms. Esther in 1961, Beulah dispersed into the rainsector bands thatbyreducing hurncane winds condensation released by this effect in 1963, Debbie in 1969, and Ginger near the eyewall, rather than just and, so, greatly reducing the force of is also ,...actable to stimulate cloud in 1971. outside the eyewall, and some cloud the winds on structuresdamage in growth Thus, these outer clouds Although this sample is quite changes appeared to be related to areas struck by the big storms could grow at the expense of the eyewall, small, seeding appears to have the seeding. But Ginger was too be significantly diminished. Also, be the storm's chimney system. In produced some interesting effect.. poorly organized for scientists to sep cause waves and storm surge are effect, Stormfury would create a The seeded,portion of Esther's arate seeding effects from the closely coupled to wind fields in a secondary e,,,e wall which would eyewall faded from the radarscope storm's natural noise level. hurricane, reduction of winds replace the initial one, effectively (which "sees" water droplets), in- Late in 1972, the decision was presumably would also moderate spreading the storm center. This dicating either a change of liquid made to concer :ate on hurncane these more destructive elements In would flatten the pressure gradient water to ice crystals or the research, temporarily suspending the those terms. Stormfury is an across the eye, and tum a severe replacement of large droplets by seeding operations in Stormfury. This experimental investment which scien hurcane into a moderate one. The much smaller ones. Beulah also intenm penod would also be used to tists expect to pay br itself many effects of seeding, Stormfury appeared to respond to seeding. the replace the aging piston powered air times over, if what is called the researchers believe, would persist central pressure of the eye rose soon craft used to carry NOAA's scientists Stormfury hypothesis is correct. from six to twelve hours, after which after injection of silver iodide parti- and instnimentation into ourricanes This hypothesis has evolved as the hurricaneother things cles and the area of maximum winds with new, turbine-powered ones scl%ntists have obtained a better remaining equalwould regain its moved away from the storm center, equipped with the best instrurnen understanding of the storms. Initially, onginal intensity. however, natural oscillations within tation available through present-day the object was to seed clouds just the hurricane could have produced technology. outside the ring o: maximum winds effects of this magnitude. in the outer portions of the eyewall 19 4C 41 Thus, the hurricane seasons Stormfury-Americas.The weather- from 1973 through 1976 saw modification side of Stormfury has Stormfury scientists fly purely re- been revived in StormfuryA--.ericas, search missions into western which schedules seeding of selected hemisphere hurricanes. These long, western hemisphere hurricanes late bumpy missions, and new in the decade of the 1970's. generations oc airborne instruments, The principal operational differ brought back data which ence between StormfuryAmericas researchers have turned into a and its predecessor missions is that significantly better understand- it is in many ways a simpler ing of hurricanes and their experiment. The missions are flown susceptibility to seeding. with similarly stringent condrtions Throughout, the emphasis has that is, storms with more than a ten- been on leaming the dynamic percent chance of coming within 50 context of the entire hurricane miles (80 kilometers) of landfall within system, from.the microphysical 24 hours of seeding are not eligible processes that control the giant for seeding. It employs the storm, to the immense circulations three NOM aircraft, an additional and interactions of the hurricane WC-130 on loan to NOM from the itself. These probes confirmed that Air Force, and the National hurricanes have the right Aeronautics and Space combination of liquid water and Administration's Galileo tl, a high-fly- developing (but still immature) cloud ing, heavily instrumented Convair towers to make seeding feasible, and 990 In the storm, advanced that hurricane winds from the instrumentation systems aboard these surface to altitude"were aboi!,t.what aircraft permit scientists to seed scientists had believed. They also where it will have the greatest effect. confirmed that revised flight pattems and then monitor that area to detect through the hurricane, redesigned to seedingconnected changes. Ars keep the aircraft in rainbands just Stormfury-Americas is a new outside tb.2 region of greatest winds Stormfury, guided by deeper for extended periods of time, could knowledge of the hurricane, and be flown safely. Parallel research led backed by greater sophistication of to development of significantly im computer models instruments, proved mathematical models of the aircraft, and other equipment. It will big storms. be through such projects that Meanwhile, NOAA's Miami-based humanity discovers whether science Research Facilities Center has been and technology can be used to tame 4 revitalized with the addition of two hurricanes, the greatest storms on new Lockheed WP3D Orion aircraft, earth. built to NOAA's special requirements. The Orions and their instrumentation systems are the most advanced airborne platforms for environmental research in the world, NOAA's C.130, still a key participant in hurricane research and Project Stormfury, is and represent a major step in man's one of two such aircraft carrying an Air Forcedeveloped Airborne Weather Reconnaissance System (AWRS), a computerized set of instruments and data ability to look at the internal dynam- analyzers controlled from the panel shown at lower left. At lower right, a scientist ics of hurricanes. NOAA's C130 launches a bathythermograph, to probe the cold wake some hurncanes leave behind also carries an advanced airborne 20them in the sea. weather instrumentation sy;tern. 44 43 Preprints, Pt.1. American nadoes," Conference on Severe Meteorological Society. P. 151.158, Local Storms, 8th, October 15-17, 1974, Boston. 1973, Denver. Reprints. American Meteorological Society. p. 108-114, Hope, John R., "Atlantic Hurricane 1973, Boston Season of 1974," Weather- wise. 23(1):13.18, February 1975, Sadler, James C., et al., Tropical Cy- Boston. clones of the North Indian Ocean," Environmental Prediction' Re- Holliday, Charles R., "Operations of search Facility, ENVPREDRSCHFAC the Joint Typhoon Waming Center," Technical Paper No. 2.73. Fifty- Mariners Weather Log. 16(6):350- eight pages, March 1973. 355, November 1972, Washington, D.C. Simpson, R.H. "The Complex Killer," Howard, R.A., et al., "Decision to Seed Oceanus. Vol. 17, pg. 22.27, Hurricanes," Science. 176(4040): Spring 1974, Woods hole Massa- 1191.1205, June 16, 1972, Wash- chusetts. ington, D.C. "Hurricane Prediction Skill: tie Mason, Herbert Molloy, Jr., Death -Progress and Prospects," Interna- from the Sea: Our Greatest Natural tional Tropical Meteorology Meeting Baum, Robert A, "Eastern North Pa Frank, Neil L, et al, "Deadliest Disaster, the Galveston Hurri- January 31-February 7, 1974, Nai- cific Tropical Cyclones, 1974" Mari- Tropical Cyclone in History," Ameri- cane of 1900, Dial Press. P. 260, robi, Kenya. Preprints, Pt.1, Amen- ners Weather Log. 19(2) 75-84, can Meteorological Society Bulle- 1972, New York. can Meteorological Society. pp. 145- 150, 1974, Boston. March 1975 Washington, D tin. 52(6) 438-444, June 1971 Miller, James E., et al., Severe Calder. Nigel, Weather Machine, The Storms, New York University, De- Sugg, Amold L, etal., Memorable Gentry, R Cecil, Experimental Hurricanes in the United States Viking Press, Inc p 143, 1975. Program to Modify Hurricanes, partment of Meteorology and Oceanography (NOAA Grant). Final Since 1873, U.S. National Weather New York World Meteorological Organization Report 1973, p. 14. Service. Technical Memorandum Davis, Harlan W, An Airborne Re WMO-No 399, P 245-254, NWS SR 56, fifty-two pages, April 1971. .search Mission into Hurncane 1974, Geneva Neumann, Charles J., et al., Ava,' Weathetwise. 26(5)208-209, "Operational Experiment in the Technical Conference, "Typhoon "Humcane Modification Modification: Proceedings of the Oct 1973, Boston Research," Bonner Meteorol> Statistical Dynamical Prediction of Tropical Cyclone Motion," Monthly Technical Conference." World Mete- Dunn, Gordon E, et al, "Honda gische Abhandlungen. Bonr No. 17, orological Organization. WMONo. Hurricanes," Technical Memorandum p 333-352, 1974 Weather Review. 103(8):665-673, August 1975, Boston. 408, 143 p., 1975, Geneva. No WBTM-SR 38 40 pp Novem- "Modifying the Greatest Storm ber 1967, Fort Worth, Texas NOAA, Space: Environmental Tse, S.Y.W., "Typhoon Development," on Earth-The Hurncane," Underwater World Meteorological Organiza- Journal. Vantage Point, U.S. Government Earle, Marshall D, "Extreme Wave ScienceandTechnology tion, WMO-No. 321, p. 122.157, 2(4)204.214, December 1970. Printing Office. Thirty-six pages, Conditions During Hurricane 1972, Geneva. Camille," Journal of Geophysical Re- 1971, Washington, D.C. "Project Stormfury," Ameri- "Typhoon Climatology," search. 80(3):377.379, January can Meteorological Society Novlan, David J., Hurricane Spawned 20, 1915, Washington, D.C. World Meteorological Organization, Bulletin. Vol. 50, No. 6, p. 404.409, Tornadoes, Colorado State Uni- WMONo. 321, p. 105-121, Geneva. Engman, E.T., et al., "Hydrologic Im- June 1969. versity, Department of Atmospheric pact of Tropical Storm Agnes," ,Science. Atmospheric Science White, Robert M., "National Hurricane Hawkins, Harry F., et al., "Sea Waming Program," American Me- Journal of Hydrology. 22:179-1;?3, Surface Temperature as a Factor in Paper No. 200. Fifty.seven pages, June 1974, Amsterdam. May 1973, Ft. Collins, Colorado. teorological Society. Bulletin 53(7): Hurricane Cloud Morphology and 631.633, July 1972, Boston. Fendell, Francis E., "Tropical Intensity," International Tropical et al., "Environmental Cyclones," Advances in Geophysics. Meteorology Meeting. January 31- Condition Differences Between Great Vol. 17, p. 2.100, 1974, New York. February 7, 1974, Nairobi, Kenya. Plains and Hurricane Induced Tor-

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