RadarObservationsofDownward-SlopingJetsassociatedwithAfricanEasterlyWavesintheCaribbean
EarlyHazardWarningPotentialofTrinidadandTobago'sWeatherRadarBradBaker1,ArleneLaing2,KennethKerr3,CarolSurath-Ali3,PaulaWellington3,GlendellDeSouza4,andMarlonNoel3
1ScienceandEducationSolutions 2CooperativeInstituteforResearchinEnvironmentalSciences(CIRES)3TrinidadandTobagoMeteorologicalServices4CaribbeanMeteorologicalOrganization(CMO)
DopplerRadar:EnhancingNowcasting&ConceptualModels
Conceptualmodelsoftropicaleasterlywavesfocusmainlyonclouds,heavyrains,andmoisture(left).However,somewavesareaccompaniedbyintensesurfacewinds,suchasreportedabove,whichmotivatethisstudy:Weinvestigate1)whetherdamagingwindscanbedetectedandwarningsissued
“…precinctsoftheDiegoMartin,PetitValley,Tunapuna/Piarco andSangreGrande…wereamongthehardesthitbyyesterday’sweaktropicalwave,whichleftcloseto25homeswithoutroofsandmanymorewithoutanelectricitysupplyforhours.”3Oct2014,A.Paul,Trinidad&TobagoGuardian
“TobagoEmergencyOperationsCentre(TEOC)iscurrentlyrespondingto114reportsofdamagedcausedbyrecentinclementweather...Damagehasbeenestimatedat800thousanddollars. Strongrains,andinparticularheavywindshaveresultedinfallentrees,roofdamageandfallenoverheadlines…”
12Oct2015,Newcenter5
timelyenoughformeaningfulprecautionstobetakenand2) thefrequencyofoccurrenceandothercharacteristicsofsucheventswithintenttoexpandourconceptualmodelofAfricaneasterlywaves(AEWs)intheCaribbeanandtherebyimproveforecastsandwarnings.
Whilesynopticanalysisandsatelliteimagesareusedtoidentifyeasterlywaves,radarprovidesopportunityformoredetailedobservationsofstormstructure,includingwinds.TheseobservationsbecamepossiblewhenaDopplerradarwas
deployedinTrinidadandTobagoin2010viatheCaribbeanRadarNetworkprogramoftheCaribbeanMeteorologicalOrganization.
1. WindJetsarecommonintheseAEWs§ Appearingin75% (16out21) AEWsobservedbytheTrinidadandTobagoradar(2014through2016seasons)
2. Themajority(~60%)appearsimilartothe rearinflowjetsassociatedwithsqualllines§ Similarinthattheydescendfromaprimarilystratiform
regiontowardsamoreconvectiveregion.§ Dissimilarinthedegreeoforganization§ WinddescendsfromtheAfricanEasterlyJetlevelorlower§ Figs.1and2showexamples
3.Exceptions totheabovearenoteworthy§ Sometimes(~20%)thewinddescendsfrommuchhigher(6– 8km)(Fig.3showsanexample)
§ Sometimes(~20%)thewinddoesnotnecessarilydescendfromabove,ratheritismaxedatthelowestlevel(Fig.4showsanexample)
Figure1:Radarobservationsofthe2October2014AEWwindeventthatde-roofed25homes.Radialvelocitiesaredisplayedontheleft,reflectivityontheright.Verticalcutsaboveandplanviews,withtheverticalcutlinesshown,below.Theintensedownwardslopingwind(notethereisvelocityfolding)appearstodescendfromtheregionofstratiformprecipitation(notethemeltinglayerbrightband)ontherighthalfofthereflectivityimagestowardsthemoreconvectiveprecipitation.
Figure2:Radarobservationsofa15July2016AEWwindevent.Radialvelocitiesaredisplayedontheleft,reflectivityontheright.Verticalcutsaboveandplanviews,withtheverticalcutlinesshown,below.Theintensedownwardslopingwindagainappearstodescendfromoneoftheregionsofstratiformprecipitation(notethemeltinglayerbrightband)towardssomeofthemoreconvectiveprecipitation.
Figure3:Radar observations of a 5 September 2014 AEW wind event. Radial velocities are displayed on the left, reflectivity on the right. Vertical cuts above and plan views, with the vertical cut lines shown, below. The intense downward sloping wind descends steeply from an altitude, estimated by the radar, of about 6 km.
Figure4:Radar observations of a 11 October 2015 AEW wind event. Radial velocities are displayed on the left, reflectivity on the right. Vertical cuts above and plan views, with the vertical cut lines shown, below. There is a low level wind maximum, which does not appear to descend from above in this case.
Results
Trinidad & Tobago
TowardsImprovedWarnings
Summary§ DownwardslopingjetsareacommonfeatureineasterlywavesoverTrinidadandTobago.
§ Alibraryofcaseexamplescouldbedevelopedtogainknowledgeofmesoscalestructuresineasterlywaves,expandconceptualmodels,andguidepublicunderstanding.
§ Trainingthereonwouldhelpforecastersincorporatethisnewinformationintoroutineoperations.
AcknowledgementsThankstoTTMSITforassistancewiththeirarchivedradardata.NCEP/NWS/NOAAFNLOperationalModelGlobalTroposphericAnalyseswereobtainedfromtheResearchDataArchiveattheNationalCenterforAtmosphericResearch(NCAR),https://doi.org/10.5065/D6M043C6.
Bulletinsareissuedbymassemail,website,socialmedia(below),andsmart-phoneApptothegeneralpublicandkeystakeholderssuchasemergencymanagers.FeedbackcomesfromrecipientsandTTMSstaff.
Current Warning System
Potential Future Warning SystemForecastsandwarningsarebeingalignedwiththeimpactsofsevereweather;withtheaimoffacilitatingmitigation.§ Requiresashiftinthinking- fromjustarainfallforecasttotheimpactof“X”amountofrainfall,given“Y”amountofsoilmoisture,and“Z”runoffcapacity,couldleadtosomedepthoffloodinginagivenarea.
§ Willrequiresharingknowledgeacrossdisciplinesoracquiringnewskillsinrelatedsciencesandsocialsciences.
§ ImpactforecastsissuedforsevereweathereventsshouldbecommunicatedinunambiguouslanguageviatheCommonAlertingProtocol(CAP),developedbythedisasteragency.
§ Publiceducationisvitalasthecapacitytorespondtowarningsmustbedevelopedwithinthegeneralpopulation,especiallythosemostvulnerablefora givenimpact.
§ Verificationoftheforecastandimpactsisnecessarytoimprovetheprocessandadapttonewinformation.
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GFS FNL 2016-07-15 1800 UTC 700 hPa Relative Humidity, Wind Velocity
GFS FNL 2011-10-15 1200 UTC 700 hPa Relative Humidity, Wind Velocity
GFS FNL 2014-09-05 1800 UTC 700 hPa Relative Humidity, Wind Velocity
EasterlyWave Easterly
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GFS FNL 2014-10-02 1200 UTC 700 hPa Relative Humidity, Wind Velocity
Flowat700hPa
SevereWeatherBulletinsarelimitedtoweatherwhichcancauseseriousdisruptionsandpossessesdamagepotential.
WiththeDopplerradar,downwardslopingjetscould,potentially,beobservedastheyshifttowardsthesurfaceovertimeandwarningscouldbebettertargetedtoparticularareas.
