Hi Emma Anne! I'm local, so I'm happy to field this one. Frankly, it's a crap shoot. It may be nice and warm, or it may be blustery. Normally, we're starting to warm up and stay warm in March. The pools are another story. Northerners seem to be fine in the pools if the air temp is approaching 80 (or even cooler.) We freeze. The pools are heated, though.
My advice is not to make any plans this far out, and then to keep an eye out on the weather at about the 10 day mark. Even then, I would pack a wide variety, and clothes that can be layered, and peeled off. Even if it's warm in the sun (and it will be, even if it's only 60s) it will be cool in the shade. Weather forecasts down here also tend to change on a dime; I planned for an overnite at WDW a couple of years back during Feb. It was supposed to be sunny and 60s; at the last minute, they revised the forecast, and it was crazy windy, cloudy, and low 50s. We froze!
And def bring your swimsuits...even if it's too cold to swim, the hottubs will be welcome after a long day of touring!
And no matter how cool it is, do NOT forget the suncreen, shades, and hats Hope this helps!