I certainly don't hold it against my raiders if they want to enjoy the one warm season most of us get instead of staying inside to raid. But it does make life difficult for me and my officers.
If your guild is like mine, you've run into this summer lull before. So what can we do about it?
1. Be willing to shift your schedule. The raiding times that most people were available in the spring may not be the best times now. Once school is over, offices transition to a summer-hour program, or new family obligations come into play, you may need to find new times to raid.
2. Encourage communication. Ask your raiders to let you know when they're going on vacation or will be otherwise unavailable to raid. Make sure people sign up for raids only when they're sure they can make it, and to update their status if something else comes up. That way you can make sure you'll have enough people for a raid ahead of time, or else give people notice that the raid might not happen.
3. Be realistic. If you've only got two healers and one tank signed up for a 25-player raid, odds are that raid isn't going to get off the ground. It's better to lower players' expectations with an advance warning, or to cancel the raid outright, than for people to set aside an evening, get prepared, and show up on time, only to be told that the raid isn't happening.
4. Lower your standards. If you have strict standards for who can attend raids, be prepared to lower those standards in order for your raids to continue. There still has to be a lower limit on what is acceptable. But if the difference between raiding and not raiding for a week is taking someone who puts out 300 less DPS than you generally like, make an exception.
5. Recruit to fill holes if necessary. It's hard to predict what will happen at the end of the summer. Some of those players who thought they were just taking a break for a month or two may never come back to the game. Other players who were gung-ho about raiding hard modes all summer may be totally burnt out by the time the next raid gets patched in. Don't count on everyone who's raiding today to be raiding in September. The worst-case scenario when adding more people is that you wind up with too many raiders in the fall. The alternative could be not having enough.
6. Be honest. If your recruiting efforts have failed and your raids are getting canceled week after week, don't be afraid to get real with your members. Call for an official raiding hiatus. Give them your best-guess time frame for how long the hiatus will last. At the same time, outline your goals and your plan for when the guild returns to raiding. Give people something to look forward to that will make it worth the wait. If it comes to this, you may lose some impatient players regardless. However, you will face less drama in the long run if you're honest about the situation than if you string people along.
Are other guilds facing the same problems mine is right now? What damage-control steps have you taken so far?