I spent 3 years in San Ramon in the central valley. FredCM is right, the rainy season usually ends in November. As the weather transforms from rainy to dry, you can experience another season that is seldom talked about, the windy season. They call them the Christmas Winds because they usually occur around year end, but a couple years ago the worst ones I've seen came the first week of Feb. We had 50 mph winds constant for a week on our mountaintop. But one thing about Costa Rica weather is the microclimates. Weather can vary significantly from one area to the next, even when not far. My biggest problem with visiting the beach areas is not so much the winds or rain, but the heat and humidity. Should be better in January, but still warm.
Fred also mentions mosquitoes. I give blood when I'm back in the states. Last year on a blood donation they asked if I had been out of the states, and of course I said yes, Costa Rica. They told me sorry, can't take you because you were in Zika territory. I found that amusing because after spending 3 months in Costa Rica, the first mosquito I saw was when I got to Arizona. Oh well, rules are rules.
I love Playa Conchal. I don't know how much you know about it, so I'll tell you our story. We took the road to the beach, and when we arrived we looked around, wondering what the attraction was. Very few people, a so-so beach. But here we were, and I wanted some photos. We noticed there were a couple cars driving on the beach, so the sand was compressed. My wife had a fit, but I drove out there with the other cars. No problem. It was a long, boring stretch, but I saw a section about half a mile down where the land jutted out, and there were some trees, so I drove all the way down the beach to that point. There was a small hill. The car tracks went over the hill but it looked ominous, so we just parked there and wandered about taking photos. Then we saw a car go over the sandy hill. Bored again, I decided to try the same, with my wife pleading me to leave. We took it slow up the hill, with our 4-wd vehicle in case, and when we reached the top, we were astonished! There was Playa Conchal! It was beautiful. And crowded. Lots of cars parked there.
We parked, and a local offered us beach chairs and an umbrella for $10. As we soaked up the sun and surf, another local came by holding a big red snapper. At first I sent him away, but then my curiosity got me and I called him back. His wife(?) had a BBQ grill set up in the parking lot, and for $25 total, we each had the most amazing fish lunch with side dishes and a couple Imperials right there in our lounge chairs. It was a memorable experience, and we almost missed it all because we didn't know much about Conchal.
One of the things we like about Conchal is the town nearby, Tamarindo. Lots of great restaurants (good restaurants are not that common in CR), eclectic shopping, and a great source of street photography. And lots of cute gals in bikinis. The area may be crowded in January, as that is high season. Lodging there is pricey, relatively speaking. We found a very nice place to stay for little money here:
http://casabambora.comIf you book there, tell Joey Will and Zonia Wagner sent you. Just for kicks. He probably won't remember us, but ...
As for other areas for photography, there are many, but they all take some driving. One that is nearby is Playa Flamingo, just a couple miles from Conchal. It's a little different in that it has a small island with pure white sand. The road to the beach is poor (most are) and not well marked. The road splits to the left and right. Right takes you to the top where you can get a great panorama shot Or the left takes you to the beach. High clearance vehicle recommended. Not as crowded as Conchal.
Other interesting areas (all are a bit of a drive from Tamarindo):
1) Monteverde Cloud Forest. Lots to see and do there, but more touristy.
2) River Celeste with its blue waters.
3) Arenal Volcano and lake Arenal - there are a couple hotels here that have amazing volcanic hot tubs.
4) Manuel Antonio National Park - the best place to see Scarlet Macaws. I recommend staying at Gaia Hotel where they have their own Macaw breeding reserve. You will see many up close without crowds. Pricey but look for mid-week rates.
If you have any questions about any of this feel free to ask.
By the way, I know that UHH has many old farts like me, and old farts often need dental work. I just returned to San Ramon for a week to get some major work done by my dentist there. My Phoenix dentist told me my bill would be $43,000 (lots of crowns, implants). So I went back to CR and got it done for $18,000. I could buy a few D850's for that savings. Quality? My dentist there is a UCLA grad and speaks perfect English. Love her work.
Anyway, enjoy your trip. Pura Vida!