Latest meteorological model consensus from the European Centre for Medium-Range Weather Forecasts indicates a daytime maximum near 21°C in Istanbul on May 17, driven by moderate southwesterly flow bringing mild maritime air across the Marmara region combined with partial cloud cover that limits peak insolation. This places the implied probability highest for 21°C at 34 percent, followed closely by 20°C at 26.5 percent, as small differences in simulated boundary-layer mixing and wind speeds can shift the peak by 1–2°C. Historical May climatology shows average highs of 20–22°C, providing context for why outcomes cluster tightly around these values. Updated guidance from the Turkish State Meteorological Service and refined high-resolution runs available later today will clarify whether conditions favor the lower or upper end of this narrow range before final observations resolve the market.