Raymarine c95 - Glossary of Weather Terms

16.10Glossaryofweatherterms
TermDenition
ColdfrontTheboundarybetweentwodifferentairmasseswherecoldairpusheswarmairoutofthewayandbringscolderweather.
CycloneAlargeareaoflowatmosphericpressure,characterizedbyinwardspirallingwinds.A“low”alsocalleda“depression”.Alsothename
usedforahurricaneintheIndianOceanandWesternPacic.
Depression
Anareaoflowpressure.Alsocalledacyclone.
Dryline
Aregionwherethereisastronggradientindewpointtemperatures.Itisoftenfoundinaregionwherestrongthunderstormsdevelop.
Forecast
Somethingthattellsuswhattheweatherisprobablygoingtobelike.
Front
Theboundarybetweentwomassesofairwithdifferenttemperatures(i.e.amassofcoldairandamassofwarmair).
High
Alsoknownasan’anticyclone’anareaofhighatmosphericpressurewithasystemofwindsrotatingoutwards.Thisusuallymeansdry
weather.Itistheoppositeofa’low’.
HighPressure
AmassofairthatpressesdownstronglyonthesurfaceoftheEarthbecauseitisbeingcooledandisthereforemoredense.
Hurricane
Aviolent,spirallingstormthatformsovertheAtlanticOcean,withwindsover120kph.Suchstormsusuallyhavealifespanofseveraldays.
Alsoknownasatyphoonortropicalcyclone.Thereare5levelsofhurricane:
•Category1—Winds7495mph(6482ktor119153km/hr).Stormsurgegenerally45ftabovenormal.Norealdamagetobuilding
structures.Damageprimarilytounanchoredmobilehomes,shrubbery,andtrees.Somedamagetopoorlyconstructedsigns.Also,
somecoastalroadoodingandminorpierdamage.
•Category2—Winds96110mph(8395ktor154177km/hr).Stormsurgegenerally68feetabovenormal.Someroongmaterial,door,
andwindowdamageofbuildings.Considerabledamagetoshrubberyandtreeswithsometreesblowndown.Considerabledamageto
mobilehomes,poorlyconstructedsigns,andpiers.Coastalandlowlyingescaperoutesood24hoursbeforearrivalofthehurricane
centreSmallcraftinunprotectedanchoragesbreakmoorings.
•Category3—Winds111130mph(96113ktor178209km/hr).Stormsurgegenerally912ftabovenormal.Somestructuraldamageto
smallresidencesandutilitybuildingswithaminoramountofcurtainwallfailures.Damagetoshrubberyandtreeswithfoliageblownoff
treesandlargetreesblowndown.Mobilehomesandpoorlyconstructedsignsaredestroyed.Lowlyingescaperoutesarecutbyrising
water35hoursbeforearrivalofthecentreofthehurricane.Floodingnearthecoastdestroyssmallerstructureswithlargerstructures
damagedbybatteringfromoatingdebris.Terraincontinuouslylowerthan5ftabovemeansealevelmaybeoodedinland8miles(13
km)ormore.Evacuationoflowlyingresidenceswithseveralblocksoftheshorelinemayberequired.
•Category4—Winds131155mph(114135ktor210249km/hr).Stormsurgegenerally1318ftabovenormal.Moreextensivecurtainwall
failureswithsomecompleteroofstructurefailuresonsmallresidences.Shrubs,trees,andallsignsareblowndown.Completedestruction
ofmobilehomes.Extensivedamagetodoorsandwindows.Lowlyingescaperoutesmaybecutbyrisingwater35hoursbeforearrivalof
thecentreofthehurricane.Majordamagetoloweroorsofstructuresneartheshore.Terrainlowerthan10ftabovesealevelmaybe
oodedrequiringmassiveevacuationofresidentialareasasfarinlandas6miles(10km).
•Category5—Windsgreaterthan155mph(135ktor249km/hr).Stormsurgegenerallygreaterthan18ftabovenormal.Completeroof
failureonmanyresidencesandindustrialbuildings.Somecompletebuildingfailureswithsmallutilitybuildingsblownoveroraway.All
shrubs,trees,andsignsblowndown.Completedestructionofmobilehomes.Severeandextensivewindowanddoordamage.Low
lyingescaperoutesarecutbyrisingwater35hoursbeforearrivalofthecentreofthehurricane.Majordamagetoloweroorsofall
structureslocatedlessthan15ftabovesealevelandwithin500yardsoftheshoreline.Massiveevacuationofresidentialareasonlow
groundwithin510miles(816km)oftheshorelinemayberequired.
IsobarAlineonaweathermaplinkingareaswithequalairpressure.
Lightning
Dischargeofstaticelectricityintheatmosphere,usuallybetweenthegroundandastormcloud.
Low
Alsocalleda’depression’thisregionoflowpressurecanmeanwetweather.
LowPressure
AmassofairthatpressesdownonlyweaklyonthesurfaceoftheEarth’ssurfaceasitiswarmedanditthereforelessdense.
MillibarAunitusedtomeasureatmosphericpressure.
OccludedFrontAnareawherewarmairispushedupwardsasacoldfrontovertakesawarmfrontandpushesunderneathit.
Precipitation
Moisturethatisreleasedfromtheatmosphereasrain,drizzle,hail,sleetorsnow,aswellasdewandfog.
PressureCentreAregionofhighorlowpressure.
SqualllineAnon-frontalband,orline,ofthunderstorms.
SupertyphoonAtyphoonthatreachesmaximumsustained1minutesurfacewindsofatleast65m/s(130kt,150mph).Thisistheequivalentofastrong
category4or5hurricaneintheAtlanticbasinoracategory5severetropicalcycloneintheAustralianbasin.
Tornado
Afunnelshapedwhirlwindwhichextendstothegroundfromstormclouds.
Tropicalcyclone
Alowpressuresystemthatgenerallyformsinthetropics.Thecycloneisaccompaniedbythunderstormsand,intheNorthernHemisphere,a
counterclockwisecirculationofwindsneartheearth’ssurface.
Tropicaldepression
Anorganizedsystemofcloudsandthunderstormswithadenedsurfacecirculationandmaximumsustainedwindsof38mph(33kt)orless.
Tropicalstorm
Anorganizedsystemofstrongthunderstormswithadenedsurfacecirculationandmaximumsustainedwindsof3973mph(3463kt).
Tropics
AnareaontheEarth’ssurfacethatliesbetween30ºnorthand30ºsouthoftheequator.
Trough
Anelongatedareaofrelativelylowatmosphericpressure,usuallyextendingfromthecentreofalowpressureregion.
Typhoon
ThenameforatropicalstormoriginatinginthePacicOcean,usuallytheChinaSea.Theyarebasicallythesameasthehurricanesofthe
AtlanticOceanandthecyclonesoftheBayofBengal.
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