Summary
Three weather systems are set to impact Arizona and New Mexico over the coming days. Former Hurricane Odalys has weakened, but is still drawing moisture northward into Arizona, aided by an upper-level low-pressure system off the West Coast. Hurricane Polo is turning east toward the Baja coast and, along with the low-pressure system, will bring additional moisture into the region. Recent precipitation has been light in the low deserts and heavier in the Mogollon Rim.
Forecasts show that as Polo moves northeast, Arizona and New Mexico will experience increased rainfall, especially in mountainous areas, with possible totals of 4 to 8 inches. The Tucson and Phoenix metro areas are expected to receive heavy rain. Possible precipitation accumulations through Wednesday in Tucson range from 0.5 to 2 inches, and about 1 inch in Phoenix, with the heaviest precipitation occurring early Tuesday and tapering off by Wednesday.
Analysis
Three weather systems will affect Arizona and New Mexico over the next few days. Former Hurricane Odalys has weakened and is at present only a low-level swirl of clouds west of Hurricane Polo. As Odalys moved north, the approaching upper-level low-pressure system off the West Coast pulled mid- and upper-level moisture northeastward into Arizona.
Hurricane Polo is beginning to turn eastward towards the Baja coast, and between Polo and the upper-level low, a lot of moisture will be pulled northeast into Arizona.
Precipitation for the last two days due to Odalys has been light in the low deserts and heavier in the Mogollon Rim.
The forecast track for Hurricane Polo is shown below. By Tuesday morning, Polo will have moved across the Gulf of California and into northwest Mexico, then south of Douglas by Tuesday evening. Hurricane forecasts are often less reliable in this area because observations are sparse, but the upper low will guide the storm northeast, so we expect this forecast track to be correct.
The combination of the upper-level low-pressure system and Hurricane Polo increased surface moisture across Arizona today, as shown by 2-meter dewpoint temperatures in the 50s and 60s across the region at 8 am this morning.
Today
This afternoon, moisture transport from Odalys is expected to produce several southwest-to-northeast bands of precipitation across Arizona, spreading eastward into New Mexico. Additional moisture from Polo will push into Arizona after midnight and is predicted to spread northward.
Tomorrow
The forecast radar reflectivity for tomorrow between 7 am and noon has the most extensive areal coverage in Arizona and New Mexico. While Polo’s center is south of New Mexico and continues moving toward El Paso, additional thunderstorms are forecast to develop west of Polo in both the Phoenix and Tucson metro areas due to moisture transport and convergence of the low-pressure system and outflow from Polo. By 4:30 pm on Tuesday, Polo will be near El Paso with a large area of showers and thunderstorms, as shown on the forecast radar reflectivity at the end of the animation loop.
The 36-hour total precipitation forecast from the HRRR-UA WRF 12Z forecast (left) and the 15Z (right) are similar, with the heaviest precipitation in the mountains of Arizona and New Mexico, where 4 to 8 inches is possible. We’re leaning towards the 15Z forecast for the Tucson and Phoenix metro areas, which are in the 0.5” to 1.5” range.
The UA WRF forecast ensemble for the Tucson (top) and Phoenix (bottom) airports shows an ensemble-mean total accumulation of 2″ for Tucson and 0.5″ for Phoenix over the next 48 hours. The peak forecast precipitation rate at the airports is around 4 am to 8 am (0.5” per hour) in Tucson and later, 6 am to 9 am, in Phoenix (¼ inch per hour). Most of the heavy precipitation will end by Wednesday.
Discussion written by Pat Holbrook and Patrick Bunn