**Thunderstorm activity over the next 48 hours is the main driver keeping the 22°C-or-below and 32°C-or-higher outcomes nearly tied at roughly 50% and 49% implied probability.** Multiple forecast models show Shenzhen under a moist, unstable airmass with scattered to moderate thunderstorms expected on September 21–22, producing cloud cover and rainfall that can suppress daytime heating while limiting nocturnal radiative cooling. This setup typically yields overnight lows in the 25–27°C range, consistent with September climatology for the region. The narrow spread between the two leading bins reflects uncertainty in how much additional cooling enhanced convection or lingering cloud cover might deliver versus the baseline subtropical warmth. Updated model runs and official guidance from Chinese meteorological agencies over the coming day will likely resolve whether conditions trend toward the cooler or warmer side of that distribution.