Recent China Meteorological Administration guidance and ensemble model runs point to a developing low-pressure system delivering heavy rainfall and persistent cloud cover across Shenzhen on May 17, limiting daytime heating and anchoring the daily high near 27–28 °C. High humidity near 80 percent combined with southerly sea breezes further suppresses temperatures below the mid-May climatological average of 29 °C, producing the tight market clustering between the 27 °C and 28 °C contracts. Model spread arises mainly from uncertainty in shower timing and intensity; earlier partial clearing could allow brief warming to 29 °C, while prolonged rain would cap readings at 26 °C. Updated 12Z soundings and the final morning forecast package will likely refine these probabilities ahead of official station resolution.