Highest temperature in Shanghai on September 11?

What this question means

Almost a dead heat: Shanghai on 11 September prices 28°C at 43% and 29°C at 41%, with 27°C and 30°C at 9% each.

Two adjacent values within two points of each other is the clearest form of a boundary problem. The underlying forecast is not uncertain about the weather — it is confident the temperature lands right around the line between two degrees, and genuinely cannot say which side.

This is the fourth Shanghai question on this board, and the set now reads 30°C on the 7th, 28°C on the 9th, 28°C on the 10th and this near-tie between 28°C and 29°C on the 11th. So: a cooling early in the week, then a flat stretch with a hint of recovery at the end.

Individually each is a modest forecast. Collectively they are a week of weather, which is considerably more than any one of them says alone.