The presence of dissipating Tropical Storm Bud and a strong southerly wind over the southwestern US will lead to an unusually early North American Monsoon for the Southwest. With the recent drought, scorching heat and widespread wild fires, the timing could not be better.
Tropical Storm Bud continues to weaken as it slowly travels northeastward toward the southern Baja Peninusla. Cool water, strong wind shear, and rugged terrain are forecast to take a toll on the tropical cyclone. By late tonight Bud will weaken to a Tropical Depression upon making landfall near the southern tip of the Baja Peninsula. The depression will spend roughly 12 hours over high terrain Friday before emerging in the Gulf of California, spreading rain northward toward the United States as it approaches Mexico. Its propagating speed will gradually increase as mutually constructive flows of a trough over the US West Coast and a ridge over the southwestern US. direct the depression to make landfall in northwestern Mexico Friday night. Thereafter, the depression will dissipate but its moisture will continue to flow northward, bringing heavy rain to northwestern Mexico and the scorching Southwestern US.
A massive moisture plume emerging from Bud’s remnants will spread northward during dissipation, with rain reaching the Four Corners by Friday evening. Showers and thunderstorms will gradually increase in coverage and intensity overnight Friday in eastern Arizona, western New Mexico, southeastern Utah, and western Colorado bringing with them a flash flooding potential. The heaviest and most widespread downpours Friday night will occur in the southern halves of eastern Arizona and western New Mexico, close to the Mexcico border where cities like Tuscon will be at the highest risk for flash flooding. Rain will be more scattered in places like Phoenix and Flagstaff.
The heavy downpours and thunderstorms will migrate northeastward into Saturday as the western trough broadens, bringing the heaviest rain generally to the west of the Rio Grand River in New Mexico and to the south and west of it in Colorado. Widespread downpours will increase in coverage and threaten Gallup, Albuquerque, and Santa Fe with flash flooding through Saturday evening. Less rain will fall further east in Las Crusces, El Paso, and Pueblo.
The Southwest will be especially prone to dangerous flash flooding this weekend as vast areas of vegetation have succumbed to ash in recent wildfires. As water rushes down mountainsides and dry river beds, poorer drainage than usual in these areas will lessen the intensity of rainfall necessary to result in flash flooding. Further escalating the danger, raging flood waters that may result from the downpours could carry debris from the fires.
Through Saturday night, Bud and its remnants will bring heavy rainfall of generally 2-6″ inches to northwestern Mexico, with higher amounts likely along eastern facing slopes throughout the storm’s dissipating stages. Extreme southeastern Arizona and southwestern New Mexico will face up to 2″ of rainfall, with locally higher amounts in the heaviest of downpours. Downpours will be more hit-or-miss in nature elsewhere, with anywhere from 0.5-1.5″ falling in lower elevation cities including Albequerque and Santa Fe. Aided by orographic lift, higher elevations of eastern Arizona, western New Mexico and southwestern Colorado stand to receive 1-3″ of rainfall. This rain may eliminate fires in San Juan, Santa Fe, Cibola, and Gila National Forests. Meanwhile, 0.5″-1″ of rain may help extinguish fires along the Sangre de Cristo Mountains in eastern New Mexico.
The Southwest will dry out Saturday night, but it it won’t stay dry for long. Heavy rain is expected to return Tuesday afternoon through Thursday as the western trough settles over the Great Basin, establishing large-scale lift and drawing moisture from the Gulf of Mexico.