Measurements at the high-elevation Lamar Observatory in the Mantaro Valley in the Central Andes of Peru demonstrate a diurnal cycle of precipitation characterized by convective rainfall during the afternoon and nighttime stratiform rainfall with embedded convection. Based on 15 years of TRMM precipitation radar (PR) swath product 2A25, the area and rain type of precipitation features (PFs) over the Mantaro Valley showing PFs with areas smaller than 25,000 km and a mean daily ratio of convective to stratiform rainfall of 40/60. Data from three wet seasons 2016-2018 reveal long-duration (6-12 hours) precipitating systems (LDPS) that produce about 17% of monsoon rainfall for warming/cooling of Sea Surface Temperature (SST) in 2016/2018 during the El Niño/La Niña in the regions 3.4 and 1.2 of the Pacific. The LPDS fraction of monsoon rainfall doubles to 34% with weekly recurrence under warm and cool conditions in the region 1.2 and 3.4 respectively, that is the El Niño Costero. Backward trajectory analysis shows that precipitable water sustaining > 80% of seasonal precipitation and LPDS originate from the western Amazon. The analysis further shows that LDPS are associated with terrain-following moisture transport at low levels from the eastern foothills of the Andes under favorable weak South America Low Level Jet (SALLJ) conditions. LDPSs consist of late afternoon shallow embedded convection in the valley with trailing stratiform rainfall that persists until the early morning of the next day. The increase in the frequency of LDPSs explains the 30% increase in rainfall during 2017.