The August through October outlook for much of the Southwest and West Coast calls for above normal temperatures, the National Oceanic and Atmospheric Administration's Climate Prediction Center said Thursday.
Some short-term easing may be in store for the region, however, with an increased chance for showers over the next week as monsoon moisture moves in accompanied by the remains of Tropical Storm Emily.
But over the August-October period, forecasters said, Arizona has the strongest possibility of hotter-than-normal readings.
A record heat wave in Phoenix has led to the, most of them homeless, leaving officials scrambling to provide water and shelter to the city's transient population.
For the first time in years, homeless shelters opened their doors during the day to offer respite from the blistering sun, which has delivered above-average temperatures every day since June 29. Police began passing out thousands of water bottles donated by grocery stores, and city officials set up tents for shade downtown.
The first deaths were reported Saturday. By Wednesday, the high still climbed to 109 degrees Fahrenheit. Even during the coolest part of the day, the mercury has failed to descend lower than 89 degrees F.
And above normal temperatures are likely along the whole West Coast, mountain states, south Texas and eastward into Louisiana, Mississippi, Alabama, north Georgia and south Florida.
Rainfall, meanwhile, is expected to be below normal in Nevada, Utah and Arizona, much of California as well as southern Oregon, southern Idaho, western Colorado and New Mexico.
The agency warned of drought developing in Arizona and New Mexico, persisting in the Northwest, Idaho, Montana and Wyoming but easing in parts of the central states and Texas.
Above normal rainfall over the next three months is expected for Virginia, the Carolinas, Georgia, Florida and eastern Alabama and Tennessee.
The forecasters noted that over the past week, many cities across the country have set or broken records for daily highs or for high minimum temperatures.
In addition, the heat index values have been particularly high over the East due to very high humidity levels.
According to the forecasters, a strong ridge of high pressure at the upper levels, centered in southeastern Utah, turned up the heat in that region.
"Typically, the warmest temperatures of the year in the southwestern United States occur in June or early July, just before the start of the monsoon season," Wayne Higgins, principal climate scientist at the NOAA Climate Prediction Center, said in a statement.