Page � of 6Tornado Risks and Hazards in the Southeastern United States HSFEHQ-07-J-0006/April 2007

Purpose and Intended AudienceThepurposeofthisTornadoRecoveryAdvisoryistoprovidebackgroundonthetornadohazardintheSoutheast.Thegeneralpopulation,homeownersandrenters,policymakers,localofficials,builders,andbuildingdepartmentsshouldunderstandthattornadooccurrenceintheSoutheastisnotarareevent.Infact,ofthetop20statesintornadofrequency,5areintheSoutheast.

ThisadvisoryalsoidentifiesFEMAresourcesthatcanbeusedtohelpdesignandconstructportionsofalmostanybuildingtype(includingresidences)toprovidesafeshelterfromtornadoes,ortohelpminimizedamagecausedbythesewindevents.

This Recovery Advisory Addresses:

Recentevents

Tornadooccurrenceoutside“TornadoAlley”…howgreatistherisk?

Canabuildingsurviveatornado?Yes!

Assessingrisk

Weatherradios

Recent EventsIntheearlymorninghoursofFebruary2,2007,asmallbutdevastatingoutbreakofthreetornadoesstruckcentralFloridafromLadyLaketoNewSmyrnaBeach.TwoofthetornadoeswereratedbytheNationalWeatherServiceasEF3andtheotherwasratedEF1ontheEnhancedFujitaScale(seetextbox).Thethreetornadoesstruckinthemiddleofthenight.Twenty-onepeoplewerekilledanddozenswereinjured.Totaldamageestimatesarestillbeingcompiledfromthisevent,butearlyestimatesarethatmorethan$150million1indamagewascausedbythesetornados.Lessthanonemonthlater,onMarch1,2007,Enterprise,Alabamaexperiencedone

Seethese2007TornadoRecoveryAdvisoriesforinformationaboutshelteringfromtornadoes,andimprovingmanufacturedhomesagainstdamagefromhighwinds:

StormShelters:SelectingDesignCriteria(TornadoRecoveryAdvisoryNo.2)

ResidentialSheltering:In-ResidenceandStand-AloneShelters(TornadoRecoveryAdvisoryNo.3)

UnderstandingandImprovingPerformanceofOlderManufacturedHomesinHigh-WindEvents(TornadoRecoveryAdvisoryNo.4)

UnderstandingandImprovingPerformanceofNewManufacturedHomesinHigh-WindEvents(TornadoRecoveryAdvisoryNo.5)

FEBRUARY 2007 TORNADO RECOVERY ADVISORY FEMA DR-1679-RA1

Tornado Risks and Hazards in the Southeastern United States

TheFujitaScalecategorizestornadoseveritybasedonobserveddamage.Thesix-stepscalerangesfromF0(lightdamage)toF5 (incredible damage). As of February 2007, the NationalWeatherServiceusestheEnhancedFujitaScale(EFScale).ThisnewscalerangesfromEF0toEF5.Seehttp://www.spc.noaa.gov/efscale/forfurtherinformationontheEFScale.

Fujita Scale EF Scale

FujitaScale

3-Second Gust Speed (mph) EF Scale

3-Second Gust Speed (mph)

F0 45–78 EF0 65–85

F� 79–117 EF1 86–109

F2 118–161 EF2 110–137

F3 162–209 EF3 138–167

F4 210–261 EF4 168–199

F5 262–317 EF5 200–234

1. St.PetersburgTimes,“FacingLifeWithoutFamily”byCatherineShoichet,March2,2007.

Tornado Risks and Hazards in the Southeastern United States HSFEHQ-07-J-0006/April 2007Page 2 of 6

ofthetop10deadliesttornadoestoimpactaschoolwhen,intheearlyafternoonhours,atornadorippedthroughahighschool,killingeightstudents.Laterthatday,atornadoseverelydamagedahospitalinAmericus,Georgia.TheMarch1stormscauseddamageandlossoflifeinseveralareasofbothstates.

Tornado Occurrence Outside “Tornado Alley”… How Great Is the Risk?“TornadoAlley”isanareaoftheheart-landoftheUnitedStatesknownforitstornadoactivity.AlthoughtheexactextentofTornadoAlleycanbedebated,mostscientistsagreethatTexas,Oklahoma,andKansasarewellknownfortornadoriskandmakeupalargeportionofTornadoAlley.

WhatmostpeoplemaynotbeawareofistheamountoftornadicactivityoutsideofTornadoAlley.FEMARegionIVhaseightstatessubjecttotornadoesandsixsubjecttohurricanes(refertomaponthispage).

AlthoughhurricaneshavereceivedmostoftheattentioninrecentyearsintheSoutheast,thethreatandriskoftornadoesisreal.ThetablebelowshowsthenumberoftornadooccurrencesforeachofthestatesinFEMARegionIV.Forthe55-yearstudyperiod,over9,700tornadoeshavebeenrecorded.TheStateofFloridaalonehasseenextremenumbersoftornadooccurrences.Forthreeoftheyearsbetween1997and2004,itexperiencedover100tornadoes(115in1997,115in1998,and105in2004).

MosttornadoesoccurringintheSoutheast(withtheexceptionofMississippiandAlabama)aretypicallyweakormoderatelystrong(classifiedasF2andsmallerontheFujitaScale).However,theseweakertornadoescanbeasdeadlyasthestrongerF3,F4,andF5tornadoes.Forexample,over50ofthe78killertornadoesthatoccurredinFloridabetween1882and2007wereF2orweaker.Further,tornadoesarenotalwayssingletornadoevents;sometimesoutbreaksofseveraltornadoesareassociatedwithalargestormsystem.NotableoutbreaksintheSoutheastinclude:

The Carolinas Outbreak of March 28, 1984

22tornadoesresponsiblefor57fatalities

Approximately1,250injuries

Approximately$200millionindamages

37%offatalitiesoccurredinmanufacturedhomes

The Kissimmee Tornado Outbreak of February 22–23, 1998

7tornadoesresponsiblefor42fatalities

Approximately200injuries

Over$100millionindamages

ThreestrongesttornadoeswereratedF3,whichdestroyedover300buildingsanddamagedmorethan7,000

States inFEMA

Region IV

Total Tornado Occurrences (�950–2005)

Total Fatalities(�950–�995)a

Number Rank

Florida 2,799 85b

Mississippi 1,429 387 2

Alabama 1,301 282 4

Georgia 1,143 111 14

North Carolina 935 82

Tennessee 788 184 7

South Carolina 718 47

Kentucky 590 105 15a. Texasisrankedhighestwith475fatalitiesforthisperiodof

time.b. InFlorida,anadditional21fatalitiesoccurredbetween1995–

2007,foratotalof166(1950–2007).

Page 3 of 6Tornado Risks and Hazards in the Southeastern United States HSFEHQ-07-J-0006/April 2007

Frequency of Recorded F3, F4, and F5 Tornadoes(�950–�998)

SOURCE:FEMA361,Design and Construction Guidance for Community Shelters, July2000

Assessing Your RiskTodetermineifyouhavealow,moderate,orhightornadorisk,usetheFrequencyMap(below)todeterminehowmanytornadoeswererecordedper3,700squaremilesfortheareawhereyourbuildingislocated.Findtherowinthe“RiskTable”(below)thatmatchesthatnumber.Next,lookattheWindZoneMap(nextpage)andnotethewindzone(I,II,III,orIV)inwhichyourbuildingislocated.FindthematchingcolumnintheRiskTableandfindtheboxthatlinesupwithboththenumberoftornadoesper3,700squaremilesinyourareaandyourwindzone.Thecolorinthatboxtellsyouthelevelofyourriskfromextremewindsandhelpsyoudecidewhethertobuildashelter.Ashelteristhepreferredmethodofwindprotectioninhigh-riskareas.

Number of Tornadoes per 3,700 Square Miles (see Wind Zone Map)

Wind Zone (see Frquency Map)

I II III IV

<� LOW Risk LOW Risk « LOW Risk « MODERATE Risk

�–5 LOW Risk MODERATE Risk « HIGH Risk HIGH Risk

6–�0 LOW Risk MODERATE Risk « HIGH Risk HIGH Risk

��–�5 HIGH Risk HIGH Risk HIGH Risk HIGH Risk

>�5 HIGH Risk HIGH Risk HIGH Risk HIGH Risk

Levels of Risk During High-Wind EventsLOW Risk–Shelteringfromhighwindsisamatterofpreference.

MODERATE Risk–Sheltershouldbeconsideredforprotectionfromhighwinds.

HIGH Risk–Shelteristhepreferredmethodofprotectionfromhighwinds.

Tornado Risks and Hazards in the Southeastern United States HSFEHQ-07-J-0006/April 2007Page 4 of 6

Alaska

Hurricane-Prone Region

Example:IfyourbuildingislocatedinNewSmyrnaBeach,Florida,youwouldseethatNewSmyrnaBeachisinanareashadedyellowontheFrequencyMap(previouspage).Accordingtothemap,thenumberoftornadoesper3,700squaremilesintheNewSmyrnaBeachareais1–5.OntheWindZoneMap(below),NewSmyrnaBeachiswithinthedarkorangearea.ThemapkeytellsyouthatNewSmyrnaBeachisinWindZoneIII.TheboxintheRiskTable(previouspage)wherethe1–5rowandtheZoneIIIcolumnmeetisshadeddarkblue,whichshowsthatthebuildingisinanareaofhighrisk.

Wind Zones in the United States

Can a Building Survive a Tornado? Yes!High-windshelterscanbedesignedandconstructedtoprotectoccupantsfromwindsandwindbornedebrisassociatedwithalltornadoes(EF0–EF5).Buildingsdesignedandconstructedabovebasiccoderequirements(aka“hardened”buildings),andnewerstructuresdesignedandconstructedtomodern,hazard-resistantcodescanresistthewindloadforcesfromweaktornadoes(EF1orweaker).Furthermore,evenwhenstrongertornadoesstrike,notalldamageisfromtherotatingvortexofthetornado.Muchofthedamageisfromstraight-linewindsrushingtowardandbeingpulledintothetornadoitself.Manynewerhomesdesignedandconstructedtomoderncodes,suchastheInternational Residential Codes(IRC2000Editionandnewer),withaloadpathtoresisthighwindforces(specifiedinbuildingcodesforhurricaneresistance)maysurvivewithoutstructuralfailure.Theprimarydamagetothesenewerhomesistothecladdingandexteriorsystems:roofcovering,roofdeck,exteriorwallsandwindows.Thistypeofdamagemaybepreventableonbuildingsthat

Notethatsomeareasoflowormoderaterisk,shownaspaleblueormediumblueontheRiskTable,arewithintheregionoftheUnitedStatesthatisalsosubjecttohurricanes(seeWindZoneMapbelow).Ifyouliveinthishurricane-proneregion,yourriskisconsideredhigheveniftheRiskTableonlyindicatesamoderateorlowrisk.

Page 5 of 6Tornado Risks and Hazards in the Southeastern United States HSFEHQ-07-J-0006/April 2007

aredesignedandconstructedaccordingtotheIRC2000(ornewer)whenthebuildingexperiencesweakertornadoesandtheoutermostwindsfromstrongertornadoes.

Formostbuildinguses,itiseconomicallyimpracticaltodesigntheentirebuildingtoresisttornadoes.However,portionsofbuildingscanbedesignedasshelterstoprovideoccupantprotectionfromtornadoes.Forinformationondesigningshelterstoresistthestrongesttornadoesandhurricaneevents,seetheTornadoRecoveryAdvisorytitledStorm Shelters: Selecting Design Criteria.Forresidentialshelters,seetheTornadoRecoveryAdvisorytitledResidential Sheltering: In-Residence and Stand-Alone Shelters.

Forexistingbuildingsthatdonothavespecificallydesignedtornadosheltersoraccesstocommunitytornadoshelters,itisrecommendedthatbestavailablerefugeareasbeidentifiedinadvancebyaqualifiedarchitectorengineer.Forfurtherinformationonbestavailablerefugeareas,seeTornado Protection: Selecting Safe Areas in Buildings(FEMA431),November2003.

Weather RadiosAllindividualslivingorworkingintornado-proneareasshouldhaveaweatherradiowithintheirhomeorplaceofwork.Aweatherradioisparticularlyimportantforthoselivinginanareathatdoesnothavestormwarningsirens.

TheNationalOceanicandAtmosphericAdministration(NOAA)WeatherRadio(NWR)isanationwidenetworkofradiostationsbroadcastingcontinuousweatherinformationdirectlyfromanearbyNationalWeatherService(NWS)office.NWRbroadcastsNationalWeatherServicewarnings,watches,forecastsandotherhazardinformation24hoursaday,aswellaspost-eventinformationforalltypesofhazards,bothnaturalandtechnological.

NOAAWeatherRadiosareavailableatelectronicsstoresacrossthecountryandrangeincostfrom$25upto$100ormore,dependingonthequalityofthereceiverandnumberoffeatures.TheNWSdoesnotendorseanyparticularmakeormodelofreceiver.

Features to look for in a NOAA Weather Radio:

Themostdesirablefeatureisanalarmtone.Thisallowsyoutohavetheradioturnedonbutsilent,listeningforaspecialtonethatisbroadcastbeforewatchandwarningmessagesthatgiveimmediateinformationaboutalife-threateningsituation.

SpecificAreaMessageEncoding(SAME)technology,aNOAAWeatherRadiofeatureavailablesincethemid1990s,iscapableofprovidingdetailed,area-specificinformation.UnlikeotherNOAAWeatherRadios,theSAMEfeaturewillfilteroutalertsthatdonotaffectyourimmediatearea.

TheNOAAradioshouldoperateonbatteriesduringtimeswhenelectricalservicemaybeinterrupted.LookforradioswithanACadapterandbatterycompartment.

TheradioshouldbetunabletoallsevenNWRfrequencies.Forthelatestlistoffrequenciesandtransmitterlocations,checktheNOAAWeatherRadioWebsitehttp://www.weather.gov/nwr.

Thehearingandvisuallyimpairedcanreceivewatchesandwarningsbyconnectingweatherradioalarmstootherkindsofattention-gettingdevices,likestrobelights,pagers,bed-shakers,personalcomputers,andtextprinters.

AutomatedSpanishtranslationsystemsarebeingexaminedforuseontransmittersservingasignificantHispanicpopulationtobroadcastSpanishtranslationsofallemergencyweatherandnaturalhazardmessagesimmediatelyaftertheofficialEmergencyAlertSystem(EAS)warningisissued.FormoreinformationinSpanish,pleasevisittheNOAAWebsitehttp://www.weather.gov/nwr/indexsp.htm.

Other methods to receive forecasts, watches, and warnings directly from the NWS:

Tuneintoyourlocalradioandtelevisionstationsforthelatestweatherforecasts,watches,andwarnings.

NWSproductsandservicesarealsoavailableontheInternetathttp://www.weather.gov/nwr.DeliveryofdataacrosstheInternet,however,cannotbeguaranteedbecauseofpotentialinterruptionofservice.

Anotherlow-costmethodforreceivingtheNWS’sessentialinformationisavailableonawirelessdatasystemcalledtheEmergencyManagersWeatherInformationNetwork(EMWIN).Thissystempresentstheinformationdirectlyonyourhomeorofficecomputer.Usersmaysetvariousalarmstobealertedtoparticularinformation,whetherfortheirlocalareaoradjacentareas.Formoreinformation,pleasevisittheEMWINWebsitehttp://www.weather.gov/emwin/index.htm.

Tornado Risks and Hazards in the Southeastern United States HSFEHQ-07-J-0006/April 2007Page 6 of 6

Useful Links and ResourcesTaking Shelter from the Storm: Building a Safe Room Inside Your House(FEMA320),March2004,2ndEdition

Design and Construction Guidance for Community Shelters (FEMA361),July2000

Tornado Protection: Selecting Safe Areas in Buildings(FEMA431),November2003