Brrr it's getting cold around here

We've noticed the nights getting slowly colder as we move north.  A few islands farther south we switched to covering up with a sheet every night, not just the nights when the trade winds were blowing down our hatches. The other morning we even woke to find dew on the deck. Then last night it dropped below 20C and in the morning all of us woke up complaining of the cold. Sheets for covering were certainly not enough! We're going to have to go shopping for some light blankets if this keeps up. And this is starting to put a real chill on my evening cockpit showers.