The Southwest US has been bone dry so far this year. Most of the region hasn’t seen rain for quite some time, and is experiencing either an ‘extreme drought’ or ‘exceptional drought,’ according to The National Drought Mitigation Center. The last time Phoenix, Arizona received rain was the 0.04 inches in March. Since then, no drop of water has fallen. So far this year, only 0.77 inches of rain has been measured, which is 2.44 inches below average.
Thankfully, some welcome relief is ahead as the remnants of Major Hurricane Bud over the eastern Pacific Ocean moves into the region by this weekend. Bud, the second major hurricane (category 3-plus) of the eastern Pacific hurricane season, is poised to make landfall near Cabo San Lucas on Baja California Thursday night as a tropical storm, bringing heavy rains and possible mudslides to this part of Mexico. Its center, likely as a post-tropical depression, will then move into either southern Arizona or New Mexico Saturday night. Tropical rains will move in, and this will allow for several inches of rainfall to occur in some locations.
Associated with Bud is a highly-anamolous and potentially record-breaking amount of moisture that will move into the Southwest. This moisture plume will begin to advance into the region on Friday, peaking in intensity over this weekend. The highest rainfall totals will near the Mexican border in Arizona where localized areas may receive over 2 inches of rain. This may lead to flooding in some areas given how dry the ground is. This comes at a time when the southwestern US generally begins to receive these rains, as monsoon season officially begins on June 15th. This season, lasting throughout the summer and ending on September 30th, brings in the most dramatic rains to the region and typically produces about half of total rainfall in a year. Leading up to the monsoon is usually the warmest temperatures. Once the rains begin, temperatures then become suppressed.
In terms of the timing of this rain, a few showers will be possible across portions of Arizona, New Mexico, and even Southern California on Friday. Saturday will be the big day as tropical rains move into the Four Corners States, with the heaviest of rain occurring in Arizona. On the leeward side of the Rocky Mountains, however, it will stay dry, so this part of the Southwest will unfortunately miss out on this needed rain. Some moisture will stream into the Northwest and even southwestern parts of Canada on Saturday as it slams up against a large dome of high pressure to the north. Therefore, a new round of rain will be ahead for this region. Then on Sunday, other than a few showers, much of the Southwest will begin to dry out. Meanwhile to the north, the northern and central Rocky Mountains will be active with numerous rain showers. This moisture will remain locked into the region through mid-next week, allowing for additional chances for rain, some of which will be heavy.