Latest ensemble forecasts from the European Centre for Medium-Range Weather Forecasts and Global Forecast System indicate Istanbul’s daytime maximum on May 18 will likely fall between 20°C and 22°C, aligning closely with the mid-May climatological average of 20–22°C maintained by the Turkish State Meteorological Service. Mild southerly flow advecting warmer continental air across the Marmara region, combined with variable cloud cover and light winds, creates the narrow spread among these outcomes, with minor differences in timing of any passing showers or breaks in sunshine determining whether the peak reaches the upper or lower end of the range. Historical data show that May temperature variability in Istanbul often stems from subtle shifts in the position of the subtropical ridge and local sea-breeze effects, leaving traders sensitive to the next model update or observational tweak before resolution.