Abstract: To investigate the spatiotemporal distribution of short-term extreme rainstorms in Fujian Province, the 1-h, 3-h and 6-h annual maximum precipitation data from 121 meteorological stations spanning 50 years (1974–2023) were analyzed, with a specific focus on diurnal (daytime vs. nighttime) variations. The spatiotemporal distributions of short-term extreme rainstorms were analyzed using the Mann–Kendall test and the regional L-moments method. Results show that Fujian Province comprises four hydrometeorologically homogeneous regions, and that most of the annual maximum precipitation series were optimally fitted with the generalized extreme value distribution, and that the L-moments method demonstrates higher accuracy compared with the normal conventional method of moments. The short-term extreme rainstorm values in Fujian Province decreased between the 1970s and 2000s, followed by a significant growth trend. These extremes in high-altitude areas shifted from nighttime to daytime, while other regions experienced increased extremes during daytime and nighttime. Meanwhile, the range of extreme rainstorms at high-altitude stations expanded annually. Stations on the southern slopes exhibited an increased probability of nighttime extremes, and those on the northern slopes experienced shorter extreme rainstorm duration over time. Influenced by complex factors involving topography and geomorphology, changes in weather systems, etc., the short-term extreme rainstorm volumes in Fujian Province generally followed a decreasing trend from the east coast to the western inland regions. High-value areas were distributed along the coast, in southern Fujian Province, and across the mountainous areas of western Fujian Province. The probability of short-term extreme rainstorms along the coast of northern Fujian Province was higher at night than during the day. The 1-h and 3-h short-term extreme rainstorm volumes along the central and southern coasts were lower at night. The interior of western Fujian Province exhibited a higher probability of daytime extremes and longer precipitation durations. The short-term extreme rainstorms along the central Fujian mountains were consistently lower in volume and probability. These patterns were governed by sea surface temperature anomalies (where warming in the western Pacific enhances southwestern moisture transport). The observed distributions were shaped by diurnal wind regimes (dominated by sea-breeze convergence with orographic lift during the day, versus the coupling of land breezes with low-level jets at night). They were further influenced by synergistic triggering from the spatial coupling between frontogenesis processes and high-equivalent potential temperature energy tongues—where terrain forcing critically amplifies nocturnal rainstorms. Diurnal moisture divergence–convergence phases, driven by wind variations, were further regulated by sea-breeze circulation and tropical systems.