Check weather reports before you plan when to do your portfolio shoot. Advance forecasts can be obtained from several online sources that allow you to block out a time when rain or storms are least likely. Temporary showers can often be used to add additional good shots. Take along a couple of colorful umbrellas and you'll have shelter for your model and a unique shot that couldn't be duplicated in the studio easily. Remember that lightning doesn't respect your right to be there, so forget the wonderful flashing lights in the background and take shelter when it arrives.
Lighting is another consideration in choosing a good location.
You want adequate light to illuminate your model, but not in her face. Study the direction and intensity of the sun and determine what direction it will be coming from when you want to shoot there. If you're on the east coast, you won't get many sunset pictures over the beach, but it's ideal for sunrises. Use the sun as a backlight or fill light, and bounce the main light onto the model with surrounding sand, or reflectors. You may also want to place a scrim over the model to completely filter direct sunlight from her, and use reflected or artificial light to provide illumination for the shot.