Well, we've gone the first week of December last year and the year before!!
We prepared for everything both years. We brought our winter coats (since we wore them to the airport anyway) and a blanket for the girls. Sweaters and pants but also shorts and bathing suits.
In 2000, it was freezing most of the week! We actually used our blanket and winter coats a couple of nights (one night it was
MVMCP). We did swim once but had to run to our towels after getting out of the pool. The nights were 40s and the days were anywhere between the 50s and finally towards the end of the week, the high 70s low 80s.
In 2001, I was prepared for the same. BUT we never used them! No need for coats or blankets, except maybe one night. Definitely didn't need our winter coats, just pants and a jersey jacket at night. It was very nice each day, 80s!!! Perfect!! We swam a lot and it was great! For MVMCP it was hot and humid!
Both years, it didn't rain much either and we never used our ponchos.
It does help a lot to read the weather before you go right up until you leave. Just prepare for everything. You never know.
Good luck!