Longer hours means that even given the usual work, socializing, yardwork, and beach trips; there will still be early morning or late night pockets in which to write. Why lay in a warm bed when you can't sleep? Sit on the back deck with a notebook and write a few lines instead. Especially if you're working with an outline, those small writing sessions will add up to something substantial over the summer.
2. Relaxed routines means chores can be a snap.
If there was ever a time to give up a full on meat and potatoes dinner and made beds, it's now. A rotisserie chicken and a salad equal a balanced dinner and if your family hasn't heard the research yet, especially in warm weather, it's a bad health idea to make the bed. Use the extra time to finish up the rest of that short story and submit it to a writing contest.
3. Summer's happenings give you more writing material to work with.
Summer brings new experiences from food to events to road trips, not to mention more restaurant patio dwellers (if you're not above eavesdropping to glean plot points for your next book) If you're writing for a commercial market, your day trips can be turned into new articles for local and national publications
Are any of these strategies ones you use already? What else helps you write in the summertime?