Tarlac has a clear dry season from November to April and a wet season from May to October. The dry months are hot but more comfortable than Manila — the inland plain cools off at night, especially in December and January.
The biggest event is the San Sebastian Festival around the patron saint's day, 20 January, which combines a religious procession with a city fiesta. The Belenismo sa Tarlac in November and December is a province-wide nativity scene competition with elaborate installations in front of churches and town halls, often huge and inventive. The Lubenas religious procession in the days before Christmas in nearby Pampanga is also easy to combine with a Tarlac visit.
Avoid the rice-harvest months of October and November in the surrounding province if you want to drive on minor roads — they fill up with grain spread out to dry on every available surface, including the lanes themselves.