**Persistent rain and extensive cloud cover forecast for September 18 are the main drivers capping daytime heating in Busan.** Multiple models, including guidance aligned with the Korea Meteorological Administration, indicate northeasterly flow bringing 5–10 mm or more of rain across the region, with probabilities exceeding 80% during peak heating hours. This combination of precipitation, high humidity near 80%, and reduced solar insolation typically suppresses maximum temperatures by several degrees relative to clear-sky baselines. Current consensus places the highest temperature most likely in the 23–25°C range, consistent with trader-implied probabilities clustering around those outcomes. Model runs show limited upside potential unless the rain arrives later or is lighter than expected, while downside risk remains if heavier showers develop earlier. Updated KMA briefings and refined model outputs on the morning of the 18th will provide the final resolution data.