There is a Hongqiao high-speed train near Hongqiao Airport. Ask the airport staff directly, and you can go to Hongqiao Railway Station and take the train.
If it is not a weekend, if it arrives before 4: 11 p.m., the ticket is relatively easy to buy.
Now it is said that the temperature on September 21th is still uncertain. If the high temperature is still there, you should wear short sleeves. If it is cool, you should wear long sleeves. It won't be very cold either. A long sleeve is enough.
about the weather, you can check it online when you come to Shanghai soon, for example, ask the sky network.