3e:null 3f:["$","title",null,{"children":"Weather Conditions for Open Water Swimming | Christian Klettner | Observable"}] 45:T633,# Weather Conditions for Open Water Swimming Wind, waves and temperature. An assessment of the suitability of the upper Port Phillip Bay for open water swimming over the next couple of days. Data sources: - [Open-Meteo](https://open-meteo.com/en/docs) - [Victorian EPA Water Quality](https://www.epa.vic.gov.au/check-air-and-water-quality) Factors in the swim score: - *Tides*: slack tides (tide change is close to zero), whether high or low tide, are better for swimming than periods when tides are rising or falling, moving tides create turbulence in the water that can reduce visibility; - *Rainfall*: recent rainfall creates bay water polution and visibility issues; - *EPA Health Advice*: the Victorian EPA provides a twice daily rating of bay water quality, historical and current water quality ratings are incorporated in the swim score, a forecast of the EPA health rating is not available, the rainfall rating is used in its place; - *Temperature*: warmer temperature are preferred to colder temperatures, both air and sea water temperatures are considered, sea water temperature is weighted higher; - *Wind and waves*: still conditions, low wind and low or no waves, mean better swim conditions than rough choppy seas; - *Wind direction*: onshore winds vs offshore winds; - *Weather*: the weather code, whether the weather is sunny, cloudy, overcast or rainy is included, sunny conditions are scored higher than rain and storms. Edit the function below, especially the thresholds which convert the metric into a scale from 0 to 3, where 0 is best and 3 is worst. 46:T270e,{ const ydomain = [0, 3]; const ydomain2 = [0, 50]; const xdomain = xdomainset === "± 7 days" ? d3.extent(data.slice(36), d => d.time) : [new Date(), new Date()].map((d,i) => d.setHours(d.getHours() + [-48, 48][i])); const xn = xdomainset === "± 7 days" ? 6 : 3; const plotdata = data.slice(36).map((d,i) => ({ ...d, epa: get_latest_epa(d.time, epa, epasites.get(site)), seatemp: wave.slice(36)[i].seatemp, wave_height: wave.slice(36)[i].wave_height, sun: sun.filter(e => e[1] <= d.time).at(-1)[0], tide: wave.slice(36)[i].tide, tidediff: wave.slice(36).map(d => d.tide).map((e,j,a) => j > 0 ? Math.abs(e - a[j-1]) : 0)[i] })).map((d,i,a) => ({ ...d, score: swimscore(d.wind_speed, d.seatemp, d.tidediff, d.weather_code, d.rain, d.epa), to: i === a.length-1 ? null : a[i+1].time })); const pltscore = Plot.plot({ width: 800, marginLeft: 50, marginRight: 50, marginTop: 15, marginBottom: 30, height: 60, color: { type: "threshold", domain: [0.1, 1.1, 3.1, 5.1, 7.1, 9.1], range: ["#2dc937", "#72d03a", "#b8d83e", "#fddf41", "#fe952b", "#fe4a16", "#ff0000"] }, x: { type: "time", domain: xdomain }, marks: [ Plot.rect(plotdata, { x1: "time", x2: "to", y1: 0, y2: 1, clip: true, fill: "score", inset: -1 }), Plot.ruleY([0]), Plot.axisY({ anchor: "right", ticks: 0, label: "Swim Score", labelArrow: "none" }), Plot.ruleX([new Date()]), ]}); const pltepa = Plot.plot({ width: 800, marginLeft: 50, marginRight: 50, marginTop: 15, marginBottom: 30, height: 60, x: { type: "time", domain: xdomain }, color: { legend: false, range: ["#2DC937", "#FDDF41","#FF0000"], domain: ["Good", "Fair", "Poor"] }, marks: [ Plot.axisY({ anchor: "right", ticks: 0, label: "EPA Health Rating", labelArrow: "none" }), Plot.rect(plotdata.flatMap(d => d.epa).filter(d => d != null), { x1: "asat", x2: "to", y1: 0, y2: 1, clip: true, fill: "healthAdvice", inset: -1 }), Plot.ruleY([0]), Plot.ruleX([new Date()]), ]}); const plttides = Plot.plot({ width: 800, marginLeft: 50, marginRight: 50, marginTop: 15, marginBottom: 30, height: 90, y: { domain: [0, 1] }, x: { type: "time", domain: xdomain }, marks: [ Plot.ruleY([0]), Plot.areaY(plotdata, { x: "time", y1: 0, y2: 1, z: null, fill: "color", opacity: d => d.sun ==="Day" ? 0.3 : 0, clip: true }), Plot.axisY({anchor: "right", label: "Tide Change |Δm|", tickFormat: d => d*d3.max(plotdata, d => d.tidediff) + d3.min(plotdata, d => d.tidediff)*(1-d) }), Plot.axisY({anchor: "left", label: "Tide Anomaly (m)", tickFormat: d => d*d3.max(plotdata, d => d.tide) + d3.min(plotdata, d => d.tide)*(1-d) }), Plot.gridY(), Plot.areaY(plotdata, Plot.normalizeY( "extent", { x: "time", y: "tidediff", curve: "catmull-rom", fill: "#607B9B", clip: true })), Plot.lineY(plotdata, Plot.normalizeY( "extent" , { x: "time", y: "tide", curve: "catmull-rom", stroke: "black", clip: true })), Plot.text(["Forecast"], { x: new Date(), y: 1, text: d => d, textAnchor: "start", dx: 10, dy: 0 }), Plot.ruleX([new Date()]), ]}); const pltrain= Plot.plot({ height: 120, width: 800, marginLeft: 50, marginRight: 50, marginBottom: 30, marginTop: 15, y: { domain: [0, 40] }, x: { type: "time", domain: xdomain }, marks: [ Plot.areaY(plotdata, { x: "time", y1: 0, y2: 40, z: null, fill: "color", opacity: d => d.sun ==="Day" ? 0.3 : 0, clip: true }), Plot.axisY({anchor: "right", label: "36 Hour Rainfall (mm)" }), Plot.axisY({anchor: "left", label: null }), Plot.gridY(), Plot.ruleY([0]), Plot.ruleX([new Date()]), Plot.areaY(plotdata, { x: "time", y: "rain", fill: "#607B9B", stroke: "black", clip: true }) ]}) const plttemp = Plot.plot({ height: 150, width: 800, marginLeft: 50, marginRight: 50, marginBottom: 30, marginTop: 15, color: { legend: false, range: ["black", "#000099"] }, y: { domain: [5,40] }, x: { type: "time", domain: xdomain }, marks: [ Plot.ruleY([5]), Plot.axisY({anchor: "right", label: "Temperature (°C)" }), Plot.axisY({anchor: "left", label: null }), Plot.gridY(), Plot.areaY(plotdata, { x: "time", y1: 5, y2: 40, z: null, fill: "color", opacity: d => d.sun ==="Day" ? 0.3 : 0, clip: true }), Plot.lineY(plotdata, { x: "time", y: "temperature", stroke: () => "Air Temperature", strokeWidth: 1, clip: true }), Plot.lineY(plotdata, { x: "time", y: "seatemp", stroke: () => "Water Temperature", strokeWidth: 2, clip: true }), Plot.ruleX([new Date()]), (index, scales, values, dims, context) => { const legend = d3.create("svg:foreignObject") .attr("x", dims.marginLeft + 40) // arbitrary offset .attr("y", dims.marginTop + 20) // arbitrary offset .attr("width", 190) // arbitrary width .attr("height", 190) // arbitrary height, manually matched to the padding legend.append(() => Plot.legend(scales.scales)).style("row-gap", "2px"); return legend.node(); } ]}) const pltwind = Plot.plot({ height: 300, width: 800, marginLeft: 50, marginRight: 50, marginBottom: 30, marginTop: 15, x: { type: "time", domain: xdomain }, color: { legend: false, range: ["black", "#000099"] }, marks: [ Plot.gridY(), Plot.axisY({ label: "Wave Height (m)", anchor: "left" }), Plot.axisY({ label: "Wind Speed (kmph)", anchor: "right", tickFormat: d => d3.format("0.0f")((d - ydomain[0])/(ydomain[1]- ydomain[0])*(ydomain2[1] - ydomain2[0]) + ydomain2[0]) }), Plot.ruleY([ydomain[0]]), Plot.ruleX([new Date()]), Plot.areaY(plotdata, { x: "time", y1: ydomain[0], y2: ydomain[1], z: null, fill: "color", opacity: d => d.sun ==="Day" ? 0.3 : 0, clip: true }), Plot.lineY(plotdata, { x: "time", y: "wave_height", stroke: () => "Wave Height (LHS)", clip:true }), Plot.lineY(plotdata, { x: "time", clip: true, y: d => (d.wind_speed - ydomain2[0])/(ydomain2[1]- ydomain2[0])*(ydomain[1] - ydomain[0]) + ydomain[0], stroke: () => "Wind Speed (RHS)" }), (index, scales, values, dims, context) => { const legend = d3.create("svg:foreignObject") .attr("x", dims.marginLeft + 40) // arbitrary offset .attr("y", dims.marginTop + 60) // arbitrary offset .attr("width", 190) // arbitrary width .attr("height", 190) // arbitrary height, manually matched to the padding legend.append(() => Plot.legend(scales.scales)).style("row-gap", "2px"); return legend.node(); } ]}); const pltwinddir = Plot.plot({ height: 50, width: 800, marginLeft: 50, marginRight: 50, marginBottom: 0, y: { axis: null }, x: { axis: null, type: "time", domain: xdomain }, marks: [ Plot.link(data.slice(36).map((d,i) => ({ direction: d.wind_direction, y2: Math.sin((270-d.wind_direction)/180*Math.PI)*d.wind_speed/20, y1: Math.sin((90-d.wind_direction)/180*Math.PI)*d.wind_speed/20, x2: new Date(d.time*1+Math.cos((270-d.wind_direction)/180*Math.PI)*d.wind_speed/20*3600000*xn), x1: new Date(d.time*1+Math.cos((90-d.wind_direction)/180*Math.PI)*d.wind_speed/20*3600000*xn) })), { x1: "x1", x2: "x2", y1: "y1", y2: "y2", clip: true, filter: (d,i) => i % xn === 0, markerEnd: "arrow", stroke: "#000099" }) ]}); return svg``; }47:[] 43:{"id":"cc40ed22391fbae6","slug":null,"title":"Weather Conditions for Open Water Swimming","thumbnail":"253ee6559d08df2c3369f73f19aeb8615bae0c4f8f2324bd5b7e6f3262d6852c","access_level":"public","create_time":"$D2026-06-16T22:33:56.764Z","update_time":"$D2026-07-01T08:58:43.081Z","view_time":null,"first_public_time":"$D2026-06-17T05:33:08.694Z","has_unpublished_edits":null,"fork":false,"stars":0,"starred":false,"owner":{"type":"team","id":"1e6bbbc1fea19b9b","login":"klettsch","name":"Christian Klettner","avatar_url":"https://avatars-next.observableusercontent.com/a2034439cf44a563da383de835ee021f6b6b0fe384e6da3aac36176d6f7b8a0a","tier":"starter_2024","bio":"Risk, finance, economic modelling, forecasting and stress testing","following":false},"version":1041,"publish_version":null,"role":null,"authored":false,"authors":[{"type":"individual","id":"9c99afc3bb345c32","login":"klettsch","name":"Christian Klettner","avatar_url":"https://avatars-next.observableusercontent.com/0d0f4aae093b36282a186ea737feb66dc7f5bb69d65e30cc5a159c34f0a77f47","tier":null,"bio":"Risk, finance, economic modelling, forecasting and stress testing","following":false}],"members":[{"type":"team","id":"1e6bbbc1fea19b9b","login":"klettsch","name":"Christian Klettner","avatar_url":"https://avatars-next.observableusercontent.com/a2034439cf44a563da383de835ee021f6b6b0fe384e6da3aac36176d6f7b8a0a","tier":"starter_2024","role":"editor"},{"type":"individual","id":"9c99afc3bb345c32","login":"klettsch","name":"Christian Klettner","avatar_url":"https://avatars-next.observableusercontent.com/0d0f4aae093b36282a186ea737feb66dc7f5bb69d65e30cc5a159c34f0a77f47","tier":null,"role":"editor"}],"comments":[],"custom_thumbnail":false,"trashed":false,"lapsed":null,"subscribed":null,"forks":0,"collection":null,"type":"notebook","body":{"titling":"auto","title":"Weather Conditions for Open Water Swimming","cells":[{"id":0,"value":"$45","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"","database":"$undefined"},{"id":654,"value":"function swimscore(wind_speed, seatemp, tide, weather_code, rain, epa) { \n let epascore = 4; \n if (epa != null) { \n if (epa.healthAdvice === \"Good\") { \n epascore = 0; \n } else if (epa.healthAdvice === \"Poor\") { \n epascore = 10; \n }\n } else { \n if (rain < 2) { \n epascore = 0; \n } else if (rain < 10) { \n epascore = 4; \n } else { \n epascore = 10; \n }}\n let score = d3.min([10, 30, 50, 999].map((d,i) => wind_speed < d ? i : null)); \n score += d3.min([20, 18, 16, -999]. map((d,i) => seatemp > d ? i : null)); \n score += d3.min([5, 10, 20, 999]. map((d,i) => rain < d ? i : null)); \n score += d3.min([1, 2, 3, 99].map((d,i) => weather_code < d ? i : null))*1; \n score += d3.min([0.05, 0.1, 0.4, 99].map((d,i) => tide < d ? i : null))*1; \n return score + epascore; \n } ","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":282,"value":"viewof site = Inputs.radio([...coord.keys()], \n { value: \"Williamstown Beach\" })","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":185,"value":"viewof xdomainset = Inputs.radio([\"± 7 days\", \"± 2 days\"], { value: \"± 2 days\" })","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":68,"value":"$46","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":266,"value":"--------------\n\nData sources","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"","database":"$undefined"},{"id":4,"value":"data = { \n return d3.json(`https://api.open-meteo.com/v1/forecast?latitude=${coord.get(site)[0]}&longitude=${coord.get(site)[1]}&hourly=wind_speed_10m,wind_direction_10m,temperature_2m,precipitation,weather_code&past_days=9`).then(data => data.hourly.time.map((d,i) => \n({ time: new Date(d+\"Z\"), \n wind_speed: data.hourly.wind_speed_10m[i], \n wind_direction: data.hourly.wind_direction_10m[i], \n temperature: data.hourly.temperature_2m[i], \n weather_code: data.hourly.weather_code[i], \n rain: i >= 36 ? d3.sum(data.hourly.precipitation.slice(i-36,i)) : null, \n color: colormap.get(data.hourly.weather_code[i])\n }))); \n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":53,"value":"wave= { \n return d3.json(`https://marine-api.open-meteo.com/v1/marine?latitude=${coord.get(site)[0]}&longitude=${coord.get(site)[1]}&hourly=wave_height,sea_surface_temperature,sea_level_height_msl&past_days=9`).then(data => \n data.hourly.time.map((d,i) => ({ time: new Date(d+ \"Z\"), \n wave_height: data.hourly.wave_height[i], \n seatemp: data.hourly.sea_surface_temperature[i], \n tide: data.hourly.sea_level_height_msl[i] }) )); \n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":707,"value":"epa = d3.csv(\"https://storage.googleapis.com/gcp-klettsch-public-bucket/vic-epa-v2.csv\").then(\n data => data.map(d => ({ ...d, asat: new Date(d.asat) })))","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":314,"value":"import {color} from \"2786b8666dea5eb6\"","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":147,"value":"colormap = new Map(color.map(d => [d.WeatherCode, d.HexCode]))","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":318,"value":"sun = { const coord = site === \"Williamstown Beach\" ? [-37.869377, 144.890839] : [-37.969674, 145.00716];\n return d3.json(`https://api.open-meteo.com/v1/forecast?latitude=${coord[0]}&longitude=${coord[1]}&daily=sunrise,sunset&past_days=10`).then(data => \n data.daily.sunrise.map(d => [\"Day\", new Date(d + \"Z\")]).concat(data.daily.sunset.map(d => [\"Night\", new Date(d+ \"Z\")])).sort((a,b) => a[1] - b[1])); }","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":630,"value":"sites = [\n { name: \"Point Lonsdale Front Beach\", lat: -38.285190, long: 144.617424, epa: \"Santa Casa\" }, \n { name: \"Williamstown Beach\", lat: -37.869377, long: 144.890839, epa: \"Williamstown\" }, \n { name: \"Half Moon Bay\", lat: -37.969674, long: 145.00716 , epa: \"Half Moon Bay\" }, \n { name: \"Mentone Beach Beaumaris Bay\", lat: -37.989002, long: 145.054430, epa: \"Mentone\" },\n { name: \"Frankston Beach\", lat: -38.142987, long: 145.114624, epa: \"Frankston\" }, \n { name: \"Geelong Eastern Beach\", lat: -38.145009, long: 144.371141, epa: \"Eastern\" }]; ","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":785,"value":"coord = new Map(sites.map(d => [d.name, [d.lat, d.long]])); ","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":790,"value":"epasites = new Map(sites.map(d => [d.name, d.epa])); ","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":719,"value":"get_latest_epa =function(asat, epa, site=\"Williamstown\") { \n let temp = epa.filter(e => e.siteName=== site).map((d,i,a) => \n ({ ...d, to: i === a.length-1 ? new Date(d.asat*1 + 8*60*60*1000) : a[i+1].asat })).\n filter(e => e.asat <= asat && e.to > asat); \n if (temp.length===0) { \n return null; \n } else { \n return temp.at(0); \n }}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":1015,"value":"","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"}],"files":"$W47","stdlib":"1"}} 44:"$43:body"