TropicalcyclonesareknownastyphooninthewesternPacificandashurricaneintheAtlantic.Thesestormsmostoftendevelopinthelateraummerandautumnoverjustnorthandsouthoftheequator.IntheAtlanticoceanthereareusuallyaboutsixhurricanesandtensmallertropicalstormseachyear.Butthereisnowaytoknowforsurehowmanystormswillhappeneachyearandhowseveretheywillbe.

　　IntheUnitedStates,expertsatthegovernmentagency,theNationlaHurricaneCenternearMiamiWatchforthedevelopmentofsevereweatherandwarnpeopleaboutthestorms.TheNationalHurricaneCenterdependsmainlyonmodernsatellitestoobservedevelopingstorms.ItalsousesinformationcollectedbypassengerairplanesandshipsandbyAmericangovernmentairplanes.

　　Satellitepicturesgivethescientistsagreatideaaboutweatherinalargearea.Scientistsusecomlputerstoincreasethesizeofpicturesthatshowadevelopingstorm.Theystudythesepicturestolearnmoreaboutthestorm’sdirectionandspeed.

　　TheNationalHarricaneCenter’sadivisoriesareconcernedmainlywithshipsintheoceanwhileastormismovingoverthewater.Butthecenter’sexpertsaremostfamousfortheirworkwhenahurricanebeginsmovingtowardsland.AtfirsttheNationalHurricaneCentermakespublicweatheradvisorieseverysixhours.Butasastormgetsclosertoland,theweatherwarningsaremadeeverythreehours.Expertsatthecenterareondutytwenty-fourhourseachdaytoprovidenewwarnings.