What kind of accommodation are you looking at? Hotel or airbnb/vrbo? The south side of Kauai is generally dryer than the north, the island is getting a ton of rain right now at the moment.
We generally go during winter so I've only been in Dec/Jan/Feb so I can't attest what the weather is like during spring, that being said we've lucked out and had great weather on our prior trips there.
Adults only or are kids going?