Recent MetService and international model guidance indicate daytime maxima in Wellington on August 20 clustered around 11–13°C amid variable southerly winds and partial cloud cover, aligning with the market’s even 26.5% splits across 10–13°C outcomes. Wellington’s exposed coastal location and exposure to the Roaring Forties mean small shifts in wind direction or low-level cloud thickness can alter surface heating rates by 1–2°C through changes in sensible heat flux and reduced insolation. A recent polar air outbreak has kept early-August anomalies below the 12°C climatological normal, but forecast guidance shows moderating conditions with limited model spread for the specific date. Traders are weighting near-term updates from MetService and NIWA guidance, as resolution hinges on the official screen-height maximum recorded at the Wellington observing site.