If the autumn weather whets your appetite for serious reading, you might consider some of the season's nonfiction titles. Anthony Burgess's 99 Novels: The Best in English Since 1939 (Summit, $10.95) is a ''personal'' selection understandably geared toward British writers. It's less understandably high on comparative mediocrities like John Braine, Erica Jong, Ian Fleming (''it is unwise to disparage the well-made popular''), and John Kennedy Toole's absurdly overrated ''A Confederacy of Dunces.'' An entertaining and occasionally provocative book, although hardly a serious piece of criticism.
A very different kind of self-portraiture is on display in Georges Simenon's Intimate Memoirs (Harcourt Brace Jovanovich, $22.95), which the celebrated novelist was impelled to write after the suicide, in 1978, of his beloved daughter Marie-Jo. It's a curious, shapeless book, reticent about Simenon's early life and practically silent about his hundreds of published books, exhaustive (and exhausting) on marital and parental traumas.
But the portrayal of his second wife, identified as ''D.,'' has the sharpness and felt depth of Simenon's finest fictional characterizations. At times ruthlessly candid, at others sentimental and self-serving, this long book is for those (many) with an addictive interest in Simenon.
Finally, here are two nonfiction books that I enjoyed as much as anything I've read this year. The Great Cat Massacre and Other Episodes in French Cultural History, by Robert Darnton (Oxford, $17.95), contains six elegant essays that reveal ''ways of thinking in 18th-century France.'' Among Darnton's subjects: the nightmarish brutality of peasant folk tales; the impact - not unlike Michael Jackson's on his teen-age admirers - of Jean-Jacques Rousseau's ''La Nouvelle Heloise''; and, in the grimly funny title piece, a ''massacre'' of cats by workers in a Parisian print shop to express their dissatisfaction with their wealthy, arrogant employers. The essays are filled with colorful details, and even relevance for our own time (in one, Darnton describes official surveillance of intellectuals, via a police inspector's information file on contemporary writers). A unique book.
Other reissues include H. L. Mencken's A Carnival of Buncombe (Chicago, $10. 95), which reprints his acerbic, vigorous ''Writings on Politics'' from the early 1920s through the late '30s. Mencken's judgments on his contemporary presidents, contenders, and other assorted pols remain remarkably fresh; the language of abuse has seldom had a more inspired practitioner. The Common Reader (Harvest, $4.95) offers the ''First Series'' of Virginia Woolf's elegant, incisive literary essays, which cover a range of some five centuries and include such famous pieces as her brilliant generalizing consideration of "Modern Fiction."