If you cannot reschedule your session, these are a few great tips to make the most out of a rainy day!
1. Bring an umbrella and/or rain boots that coordinate with your clothing choices or opt for a clear bubble umbrella. (Avoid logos/writing)
2. Many venues and private estates, museums, botanical gardens, etc. allow an hourly rental of their property for a minimal fee if you want to stay dry.
3. Try to find cover using building overhangs, archways, etc.
4. Once you have gotten some great images, just have fun with it! Jump in puddles, stand in the pouring rain and kiss!!