As of this writing, there are a few weeks until the beginning of school. Stores are already beginning to carry Halloween candy, and my friends who work on paid search campaigns for the holidays are measuring the days until Christmas.
If you're writing things that are at all popular, it's worthwhile when you're preparing in advance for what to say to have enough of a sense for the future that you can write about it well before it happens. The ability to conjure up a late October chilly evening while it's still August hot is a technique that can be practiced. This is especially true if your blog is old enough to have gone through a year or two, and if you have some kind of analytical tool that can tell you what time of year people start finding your old writing from last year about a subject for this year.
This graph from Google Trends shows search traffic for Halloween, showing it starting to grow in mid August through mid October, peaking in mid October, and then zeroing out again November 1 as we start to get ready for the next season. If you're writing about Halloween anything, this tells you that you can't get started at the very end of the season - and, if anything, if you wanted to start a Halloween weblog, you'd start it at the beginning of August for the season so that you'd have a good three month's worth of content ready for the peak time.
Every seasonal topic has a yearly ebb and flow, and if you're writing to that topic you can tell in advance when you need to pay attention. Google Trends will tell you that poison ivy's peak season is just before blueberry season, and that lots of people look for information about wine between Thanksgiving and New Year's Day. And I can tell you from past experience in writing about Hallloween that people really want to know trick or treating hours as soon as they can find them, which might be a few weeks before the big night.