Hi Sheila
The weather is likely to be fairly hot - a minimum of 25 degrees celsius, possibly rising to the low 30s. Bear in mind that it's also the tail-end of the rainy season, so make sure you have something waterproof to hand.
You certainly won't need to dress formally. It will be warm so I would advise wearing what you would for an evening with friends... in a warm climate.
I'm sure you'll have a wonderful trip - India is a fascinating country.
Kind regards,
Olly, your editor