We're pretty lucky here in the Bay Area with a fairly large wind season, some catching sessions as early as March and all the way into October, or even November. Live2Kite "stoke tip", learn to hydrofoil. This will greatly extend your sailing season. Foiling allows you to get sessions with a very minimal amount of wind.
Our local SFBA (San Francisco Boardsailing Association) just put together a great guide to catching kitesurfing sessions here during the off-season.
[....The end of the season really just means the wind becomes more unpredictable. The wind we do get tends to be pre-frontal storm generated wind from the South and post storm "clearing" North West winds. We also occasionally get wind that blows from the E or NE wind. These winds tend to be gusty and intense at most bay spots.
A good rule of thumb to follow for safe sailing is the "100 degree rule." This means the air temperature plus the water temperature should be greater than or equal to 100 degrees F to be sailed comfortably. One of the biggest things you have to watch out for in cold water sailing is hypothermia. Hypothermia is a general cooling of the entire body.....]
PSA: Are you a member of the SFBA? Do you know what the SFBA is? Take a moment to check out their page and become a member.