Because of the inland location and the high elevation of Colorado, the state does not receive hurricane activity much at all. However, there are occasional cases of such cyclones, most of which originating in the eastern North Pacific, who's remnant moisture can inflict (heavy) rainfall, thunderstorms, gusty winds, and in rare cases, mountain snowfall. Climatologically, most tropical cyclones in the eastern North Pacific basin are steered away from land to begin with and, in the occasional case that cyclones do traverse land (specifically that of the Baja California Peninsula and northwestern Mexico, they must undergo a recurvature at a certain set of track angles. Not all of such remnants come from the eastern Pacific however. For example, the non-tropical remnants of Typhoon Nuri in 2014 would significantly contribute to a record-breaking cold wave, significantly dropping temperatures to sub-zero in large swaths of the state throughout much of that November.
Tropical cyclone-related phenomena is vastly uncommon, but not impossible, with several meteorological events caused by/associated with (former-)hurricanes and typhoons observed since 1950 (some of which indirectly). Most of these events, are byproducts of eastern North Pacific hurricanes; which form closer to Mexico than usual and are recurved towards land (specifically the Baja California Peninsula and Gulf of California) by an approaching trough. This is most common in the Autumn months of hurricane season; between August and October, most often September.
October 1911: In Early-October 1911, flooding of the San Juan River experienced a record-breaking flood, washing out every bridge in Archuleta County with entire houses floating downstream. Flooding such as this was theorized to have been the result of remnant moisture from a Pacific hurricane.[1]
September 1938: Over a decade later, the remnants of a hurricane in the autumn of 1938 made their way up to Colorado, dropping enough rainfall to raise peak flow of the San Juan river to 1100 cfs.[1]
September 1958: It would take another two decades for documentation of another tropical cyclone bringing moisture to the state, this time in the form of a tropical storm, which also brought monsoon-enhanced rainfall, though totals are unknown.[2]
August 1960: Only two years after, Hurricane Diana would deliver rain-producing moisture to the states of Colorado and Arizona[2]
September 1970: The following decade would begin with Tropical Storm Norma making the journey to the southwest United States, where the associated moisture and unstable air caused rainfall in Colorado. The San Juan River would reach the second-highest rain-generated flow caused by tropical cyclone remnants, at 6580 cfs.[1]
October 1971: In the first couple days of October 1971, the remnants of Hurricane Olivia would lead to precipitation throughout Colorado, ending an ongoing drought. Snowfall was even reported at higher elevations of the Rocky Mountains.[1]
September 1972: For the third straight year, a Hurricane Hyacinth managed to bring precipitation to the state, although not much else is known.
October 1972: Just a month after Hyacinth, the remnants of Hurricane Joanne would bring large swaths of precipitation to the southwestern United States, with maximum rainfall values in Colorado topping out at 2.1 in (53 mm) in Fort Lewis.[3]
August 1977: Moisture associated with the remnants of Hurricane Doreen ended drought-conditions in the state with rain-generated flow of the San Juan River peaking at 1150 cfs.
September 1982: The remnants of Hurricane Olivia would cause precipitation over large swaths of the Southwestern United States over the last couple days of September. Although specifics are unknown, snowfall was observed over higher elevations of the Rocky Mountains, including Colorado.
October 1982: Not even a week after Olivia's passage, the remnants of Hurricane Paul brought a mix of rain and snow through Colorado.
October 1983: Despite having degenerated well southwest of Southern California almost a full-week prior, the remnants of Tropical Storm Octave produced some inclement weather over far southwestern Colorado.
October 1985: The remnant frontal system associated with Hurricane Waldo ran through the Great Plains, generating isolated areas of minimal rainfall in far southeastern Colorado.
June 1990: The upper-level remnant of Hurricane Boris traversed much of the western United States, briefly moving over northwestern Colorado. However, little to no impacts were observed.
August 1992: The wettest-known tropical cyclone (remnant) in the state, the remnant disturbance of Hurricane Lester ran through Colorado during August 23–25. Rainfall totals in Colorado peaked at 5.35 inches (136 mm) in Wolf Creek Pass with lesser totals of 1–5 inches (25–127 mm) seen all throughout the state.
August 1993: The remnants of Hurricane Hilary delivered some moisture to portions of Colorado before merging with a cold front over the Midwest during Late-August 1993.
September 1997: Remnant moisture associated with Hurricane Nora delivered isolated areas of precipitation in far western Colorado, although it remained minimal.
August 2003: After 6 years with no known impacts associated with tropical cyclones, Hurricane Ignacio brought moisture as a remnant low to the southwestern United States, with areas in Colorado seeing over 25% of warm-season precipitation from the system.
September 2004: The upper-level remnants of Hurricane Javier would bring isolated patches of rainfall to southwestern Colorado, with precipitation generally kept to 1-3 inches (25–76 mm).
July 2008: Rare for its time of year and place of origin, Hurricane Dolly became the first known Atlantic hurricane to directly affect the state of Colorado. Despite this however, impacts were minimal with only small, isolated areas of minor precipitation observed. Rainfall in the state peaked at 1.9 inches (48 mm) in the town of Her.
September 2013: The duo of Hurricanes Ingrid and Manuel caused a slow-moving frontal system to stall over Colorado. This frontal system, aided by the moist tropical airmasses of the two aforementioned hurricanes, caused a catastrophic flooding event over the Front Range. 24-hour rainfall values in Boulder, Colorado on September 12 were as high as 9.07 inches (231 mm), with 17 inch (430 mm) values over the week accounting for almost all of the city's annual precipitation. Damages from the floods exceed $1 billion (2013 USD), with 8 fatalities.
June 2015: Hurricanes Andres and Blanca both went on to affect the Southwestern United States as remnants in June 2015, less than a week apart. Both remnants only managed some scattered thunderstorms across the state, however.
June 2018: The remnants of Hurricane Bud brought drought-relieving moisture to parts of the state, slowing the growth of wildfires in the Rocky Mountains. The moisture also caused flash flood watches in Southwestern Colorado.
October 2018: Remnant moisture associated with Rosa produced isolated shower and thunderstorm activity over Colorado, although impacts were minor.
