Dolly will move onshore in northeastern Mexico at midweek, while Norbert will move northwestward near the west coast of Mexico.
A great deal of Dolly's moisture will be squeezed out over the mountains in Mexico, where flooding is almost certain. However, some shower and thunderstorm activity will affect part of South Texas. The moisture will not stop in South Texas and northern Mexico.
Showers and thunderstorms not associated with Dolly were already in place over northern Mexico and were ready to be tapped by a southerly flow from Norbert.
According to AccuWeather Senior Meteorologist Ken Clark, "After the monsoon spigot got turned off early last week, this will mark the return of showers and thunderstorms to most of the Southwest including all of Arizona, southern Nevada and at least southeastern California."
Portions of New Mexico, Utah and Colorado will also be on the receiving end of showers and thunderstorms.
The bulk of the rainfall will occur this weekend.
As is often the case in the Southwest when downpours occur, there will be a risk of flash flooding, mudslides and road washouts. This is due to the rocky terrain, steep hillsides and arroyos. Runoff is often very rapid and can fill the typically dry stream beds.
California is in desperate need of rain with much of the state in extreme or exceptional drought.
Water levels on area lakes and reservoirs continue to plunge due to stingy rain and mountain snow from this past winter.
Significant rainfall has occurred during the monsoon in areas farther to the east over the Four Corners states, but more rain is needed.
Rainfall From June 1 to Aug. 31, 2014
Typically, very little or no rain falls during the summer and early autumn over much of California.
Rain is unlikely to reach central and northern California during the pattern later this week and weekend, except for perhaps part of the Sierra Nevada.