A yellow weather warning for heavy rain is in place for most of the county tomorrow (Sunday).
The Met Office is warning of potential flooding in areas with some potential interruption of power supplies because of lightning.
The warning is in place for the whole of Northamptonshire apart from towns and villages in the north east of the county such as Oundle and Thrapston.
The Met Office says the warning is in place from 12.15am to 8pm.
A Met Office spokesman said: "Although some places will stay dry, heavy rain may cause some localised flooding and travel disruption."
Temperatures are expected to reach a high of 19C.