We just spent a month in Puerto Viejo and are planning to return next year for longer..
The weather was ... interesting but way better than what the US was experiencing. You don't need a jacket but I would highly recommend a waterproof rain jacket; the rain is warm. For the most part there were periods of sun everyday and some days were an absolute 10...
I want to give travelers 2 "warnings" that will help in their safety.
1. Respect the rip current.. If the seas look angry DO NOT BOTHER GOING IN ABOVE YOUR KNEES. Punta Uva is the most protected beach, on those 'angry' days try going there that is your best bet for an ocean swim. If you're lucky enough to be on a beach with a lifeguard (Cocles) then stay in yellow flag areas. Talk to (and thank) the lifeguard. Do not do what I did at Playa Negra and jump right in and swim out past the breakers... i got a little stuck and lucky for me there was a surfer out there. He pointed me the right way back in... lesson learned.. The very next day we were at the same beach and a 20 something couple drove up and jumped into the waves.. in less than a minute the girl couldn't get back in, Her boyfriend took off to Banana Azul hotel 300 m. back and I kept an eye on her, a local lady warned me NOT to go in after her, she said there were 5 drownings last year on this beach. alone. The girl was a strong swimmer but was getting crushed by the big waves not more than 50 meters out.. Her boy friend returned with a lifeguard float and swam out and saved her. She collapsed on the sand and was thankful to be alive. Follow the crowds into the ocean, if they aren't swimming then that in itself is a warning. Which brings me to point number 2.
2. Respect the locals. We went back to the same beach for the 3rd day in a row, this location was about 300 m. past Banana Azul on Playa Negra. Awesome beach, we were the only ones there. This was our 3rd day in the same location and started feeling pretty 'at home'. I was getting the place set up, lashing together some bamboo and putting some palm fronds on top to get some shade. Feeling pretty pretty good. I had my iphone, kindle, hammock, swim fins, flashlights, multi-tool, $100 in cash, crossword puzzle book.. we were going to be there all day.. It was about noon, I went down the road looking for more palm fronds.. Well meanwhile back at where we were set up... a man with a 3' foot machete (which are very scary looking) confronted my wife and took off with her pack.. he realized there was another pack my wife had gathered. He returned, raised the machete above his head and demanded "Gimmee", By the time (10 minutes total) I got back he was long gone and my wife was totally broken down. He did other things that made her believe he was going to molest her. We ran to Banana Azul. They couldn't have been more helpful (thanks Roberto) and called the Police Tourista..We spent the rest of the day in Bri Bri making reports.. I should not have
a. brought so much stuff to the beach (only bring what you can afford to lose)
b. left my wife alone on that beach
I am not going to say we should not have been on that beach, that punk is the one who should not have been on that beach.