It all depends on cold fronts and their passage,
but I would say (based on living here 28 years) days 70's nights in the 50's nominal
extreme would be lows of 40's to highs of 60's after a cold front passage for a day or two but then it will be very sunny and clear with a N wind of say 10 to 15 MPH
Jan is mostly a dry month with only 5 or 6 days of rain for a brief time total for the month
Jan to Mar is the best weather for the state IMHO
No hurricanes and great golfing weather
The beach water is from the high 70's in the south to high 60's north.
Lots of Sun, bring sunscreen
Get to Vero Beach I buy the first drink
