Wednesday, September 17, 2014

Tropical Weather in the Desert Southwest - Odile is a Big Deal

A few days ago Odile was a Category Four Hurricane off the west coast of Mexico, and as of this morning was still a weak tropical storm. Odile fell apart over northwestern Mexico during the day, and is now just a shell of its former self.  However, the remnants of Odile will still have quite an impact on weather for the next few days, first across the southwestern U.S. and then perhaps across the extreme southern U.S.

Map shows the expected position of the remnants of Odile [D] at 11:00 p.m. PDT September 17.

The remnants of Odile were already feeding plenty of moisture into the Desert Southwest. Storms were bubbling up today across Arizona and New Mexico while some isolated storms popped up in southern California.

Yesterday there were some rare severe thunderstorms in southern California. Wind damage was reported in and around San Diego, where numerous trees and light poles were toppled and small planes were flipped over at Montgomery Field Airport. One inch hail was reported near Joshua Tree, CA in San Bernadino County.

San Diego radar image for 3:15 p.m. PDT September 16. Storms were moving to the west.
Conditions across southern Arizona and New Mexico today were decidedly tropical. It was quite humid with dewpoints generally in the mid to upper 60s. The dewpoint in Phoenix this afternoon reached 72°F, a level that is rarely seen there. Swamp coolers (evaporative air conditioners) don't work very well when the dewpoint is high. 

There are a combination of factors that will make the next few days messy, to say the least, in the Desert Southwest. CoCoRaHS observers in the region will be getting a lot of measurements in over the next several days.  Although we are the tail end of the summer monsoon season, there will be heavy showers and thunderstorms because of the plentiful moisture being fed into the region. Weak flow in the upper atmosphere will provide for little steering of the showers and thunderstorms, and those that develop could remain over a relatively small area for much of the storm's lifetime. That means potentially heavy rain for a long period of time.  That same weak upper flow also means that the leftovers from Odile will be slow to move out of the region.

500 millibar map for 5:00 a.m. PDT this morning. The circulation of Odile is caught in a ridge over the Southwest.

The NWS Weather Prediction Center is expecting as much as 4 inches of rain from southeastern Arizona through southern Arizona and into western Texas, with some locally higher amounts possible.

Rainfall forecast through 5:00 p.m. PDT Saturday, September 20.

Flood watches are in effect for large portions of Arizona and New Mexico.

Flood watches (dark green) and flood advisories (light green) in effect as of 5:00 p.m. PDT

Here is a broader picture of the rainfall expected in the southwest and across the country the next three days.

Quantitative Precipitation forecast for the 72-hour period ending 5:00 p.m. PDT Saturday, September 20.

The showers and thunderstorms are most numerous tonight south of the Arizona-Mexico border but are steadily feeding northward. The Tucson NWS office has a nice summary of daily and monthly rainfall records for a number of locations in southern Arizona on their web site. 

Tucson, AZ radar at 5:39 p.m. MST September 17

1 comment:

  1. Strangely enough with dew points in the 60's all day this area of Arizona, the Verde Valley at Cottonwood, received very little rain with only trace amounts or zero being reported.