I have been in January a number of times. My best advice is to pack for a range of temperatures. I have seen high temps in the 80's with full sun and it was pretty hot during the middle of the day. Then after the sun sets it cools pretty quickly down into the 60's and with a breeze it can be a little chilly so you need a jacket or long sleeve shirt to put on. I have also seen a day or two where it is cloudy with light rain and a high in the 60's cooling into the lower 50's after the sun sets. Generally though the weather can be quite nice that time of year with sun and 70's during the day and cooling into the 60's after sunset.