It depends on where you want to go. Here's a map that will give you an idea of general weather patterns. Mouse over it to see rainfall by month. Places like the Osa and Manuel Antonio tend to get a lot of rain then, but other areas don't.

http://costa-rica-guide.com/Weather/WeatherMap.html

you can reduce your chances of all day rain by heading to Guanacaste but there is still no guarantee. Check out towns like Tamarindo and Flamingo. The great thing about travelling in September is that it is the low season and you can get great rates on lodging at hotels and vacation rentals.

www.rpmvacationrentals.com can give you a large selection of condos and houses for rent in Tamarindo. If you are looking for a hotel, check out capitan Suizo, the JW Marriott, or the Westin.

http://www.hotelcapitansuizo.com
www.tamarindo.com

You Should not wait to travel . In Costa Rica is not a specific season , could be that in the capital is raining but in the coast could be hot and sonny.It depends on where you will go !
Also you can enjoy many activities during raining season.

Thanks everyone! September it is. I agree, I don't like to wait when I have a chance to take a trip.

I would like to SCUBA dive one time while I'm there but I know the south west is the best but also has the most rain. So, I plan to skip the far south and maybe I will have the chance to dive elsewhere.

Does it typically rain ALL day or more commonly in the afternoons/evenings? As a Florida girl, I'm used to the latter and will just plan activities earlier in the day if that's the case.

i have lived in Costa Rica for over 10 years: Southern Zone, Northern Zone, and have a place in Central Valley for city trips. September, October are peak rainy season. No matter where you are you will have rain. In Guanacaste, where I have been for over the majority of the time, there are some sunny mornings but the rains come in by late morning, mid afternoon. Many nights are spent without power. If you are in the most Northern part of the country you may have sunny/cloudy days....if you are lucky. I do not have friends or family down during these months and we close our business....as do many in the tourism industry.

I think September is best time to go to Costa Rica. Climate there is must.

Linzy, have you thought about going to Belize at all? If you're into SCUBA or snorkeling, Belize has a lot more of that than CR.

Thanks everyone! Looks like we will be going in the first week of November. Not much better but hopefully slightly less rain.

Valconogirl, good advice on Belize. We are still going to CR but looks like I will Belize to my growing trip list!