"Extreme" heat envelops Phoenix, 42 million people under warnings
The globe's historic heat records have received massive media attention, but at a regional level, excessively hot weather is building across the U.S. and is likely to last well over a week.
Why it matters: Globally, there have been four straight days of temperature records set or tied since July 3, along with seven straight days of average temperatures breaching 17°C (62.6°F), which previously had not occurred since at least 1940.
- Potentially historic and deadly heat is already present in the Southwest, including California and Arizona. Parts of Texas and Florida are also mired in extreme heat, and conditions in each of these areas are forecast to worsen.
Context: Climate change is causing heat waves to be more likely and intense. Record global ocean temperatures are contributing to heat waves over land, and sending humidity levels soaring in some regions.
- This elevates the heat index, which is a measure of how hot the air feels to the human body.
The big picture: Dangerously sweltering conditions are expected to intensify this week across the Southwest. That puts daily, monthly and some all-time records in jeopardy from the deserts of southern California to southwestern Texas.
- In Arizona, the NWS warns that residents of Phoenix be prepared for temperatures into the 110s°F for this week and into next, with the city's milestone for the most consecutive 110-degree days likely to fall. The current record stands at 18 days.
- As the weekend approaches, the heat is likely to worsen to "extreme" levels, per the NWS, as an area of high pressure aloft, or heat dome, moves overhead and strengthens.
- At that time, a rare high temperature of 120°F may be within reach. The city's all-time high temperature record is 122°F.
- Long-lasting heat waves are especially dangerous for public health. During this extreme heat event, overnight low temperatures are forecast to remain elevated, well into the 80s and 90s, providing no relief for people who may find themselves without access to cooling.
Zoom in: Florida is on a hot streak as well, and temperatures well above average are forecast to continue this week and next for much of the state.
- It is unusual for the Sunshine State to see heat indices up to 110°F, but that is likely to continue during this event.
- Extremely high ocean temperatures along the Florida coast, with unheard-of readings of 90°F or greater, are helping to fuel the heat.
- Such water temperatures could cause coral bleaching in the Florida Keys, since warm water corals are extremely sensitive to spikes in water temperatures.
What's next: There are signs that the heat dome over the nation's southern tier will actually expand its influence over time, bringing unusually hot weather to the southern Plains states by the weekend as well.