September 9, 2026

This region carries the largest and most dangerous set of alerts in the country today, and nearly all of it is heat.

Extreme heat warnings are in effect across a wide area of the desert Southwest and southern California. The Las Vegas office covers Death Valley National Park, the Northwest Deserts, the Cadiz Basin, the San Bernardino County side of the Upper Colorado River Valley, Lake Havasu and Fort Mohave, the Arizona sides of Lake Mead and Lake Mohave, northeast Clark County, western Clark and southern Nye counties, the Las Vegas Valley, and the Nevada sides of Lake Mead and Lake Mohave, from 10 AM to 8 PM Thursday. The forecast highs are 112 to 116 in Death Valley and the Colorado River Valley and 105 to 110 in the Las Vegas, Moapa, and Pahrump valleys.

The Phoenix office covers the Imperial Valley and southwest and west Imperial County in California with afternoon temperatures of 106 to 114, and Parker Valley, central La Paz County, the Palo Verde Valley, and the Chuckwalla Valley with 102 to 111, both until 8 PM Friday. The San Diego office covers the Coachella Valley, the San Diego County deserts, and the San Gorgonio Pass near Banning at 106 to 110 through Friday evening, and the Inland Empire valleys of San Bernardino and Riverside counties at up to 107, along with the San Diego County inland valleys at up to 106, the Santa Ana Mountains and foothills, inland Orange County, and even the San Diego and Orange County coastal areas, where the warning reflects mid 80s at the beaches with overnight lows only in the low to mid 70s.

That last detail is the one that does the damage. What makes this event dangerous is not the afternoon number but the overnight number. When the low stays in the 70s or 80s, a house without air conditioning never resets, and the people inside start each day with less reserve than the day before.

Heat advisories, one level down, cover a great deal more of California. The San Francisco office has one until 10 PM Thursday for the Bay Area and Central Coast, including San Francisco itself, the San Francisco Peninsula coast, the East Bay interior valleys, the North Bay interior valleys and mountains, the Marin and Sonoma coastal ranges, and the Point Reyes National Seashore, with temperatures running 10 to 20 degrees above normal by day and by night. The Sacramento office covers the central and southern Sacramento Valley, the northern San Joaquin Valley, the Delta, and the Motherlode between 1,000 and 3,000 feet with highs of 97 to 104. The Hanford office covers Merced, Madera, Mendota, Los Banos, Dos Palos, Coalinga, and Avenal with highs to 102 and morning lows to 75. The Los Angeles office covers downtown Los Angeles, the eastern San Fernando Valley, Calabasas and Agoura Hills, the Santa Monica Mountains, and the Los Angeles County beaches with a range of 92 to 108, and has an extreme heat warning for the Santa Clarita Valley, Cuyama Valley, Santa Lucia Mountains, southern Salinas Valley, and San Luis Obispo County inland areas.

The National Weather Service instruction text on these products is the same everywhere: drink fluids, spend the hottest part of the day in an air conditioned room, stay out of the sun, wear light and loose clothing, and move strenuous work to early morning or evening. Check on relatives and neighbors, particularly anyone living alone without air conditioning. Never leave a child or a pet in a parked vehicle, even briefly. The Weather Service also passes along the Occupational Safety and Health Administration guidance to schedule frequent rest breaks in shade or air conditioning for outdoor work. Anyone overcome by heat should be moved somewhere cool and shaded, and the Weather Service treats heat stroke as an emergency call to 911.

A Bay Area specific note: heat advisories in San Francisco land differently than they do in Phoenix, because a much larger share of housing has no air conditioning at all. If that describes your home, the practical version is to close windows and blinds on the sun side during the day, open up after sunset once the outside air is cooler than the inside air, and plan to spend the hottest hours somewhere with cooling. Libraries and community centers in most Bay Area counties open as cooling centers during these events, and county public health pages list them.

In Hawaii, the National Weather Service office in Honolulu has a flood watch for the Big Island through Wednesday afternoon, covering Kona, Kohala, the Big Island interior, summit, south, southeast, east, and north. The cause is a band of moisture on the eastern flank of Hurricane Lowell moving west over the island. A flood watch means conditions favor flooding but it has not begun, and the official instruction is to monitor later forecasts and be prepared to act if flash flood warnings are issued. A high surf advisory for west facing shores of the Big Island runs through midnight, with breaking waves of 6 to 8 feet.

Hurricane Lowell itself has pulled north of the islands and the hurricane warning for Kauai and Niihau and the tropical storm conditions on Oahu have ended. What remains is cleanup and the trailing moisture. On Guam, the Tiyan office has a flash flood warning and a flood advisory in effect through Wednesday afternoon local time.

Anywhere water crosses a road, the National Weather Service's Turn Around, Don't Drown rule applies. Do not drive into it.

The National Interagency Fire Center, which coordinates wildfire response across federal and state agencies, reported 64 uncontained large fires nationally in its September 8 situation report, with the national preparedness level at 4 on a 5 point scale. Year to date the country has recorded 53,665 fires and about 8.4 million acres burned, which the center puts at 125 percent of the ten year average for fire counts and 157 percent for acreage.

Three of those fires are in California. The Plaskett fire is at 29,862 acres and 47 percent contained with evacuations in place and structures threatened. The Timber fire is at 25,380 acres and 27 percent contained with structures threatened. The MP18 fire in northern California is at 7,601 acres and 98 percent contained and effectively finished.

If you are near Plaskett or Timber, evacuation status comes from your county sheriff or office of emergency services, not from a national situation report. Both fires still have a live perimeter.

In Hawaii, the immediate infrastructure picture is recovery from Lowell on Kauai, Niihau, and Oahu. Restoration after a hurricane is usually measured in days rather than hours, and food safety becomes the household question once a refrigerator has been off for a while. The Food and Drug Administration's standing guidance is that a closed refrigerator holds safe temperature for about four hours and a full freezer for about 48 hours, and that perishable food held above 40 degrees Fahrenheit for more than two hours should be discarded rather than judged by smell.

California has an open Federal Emergency Management Agency Fire Management Assistance Grant, FM-5662, issued August 4. These grants reimburse state and local firefighting costs and do not pay households.

No power outage events or water system notices are reported for Arizona or Nevada.

No air quality alerts are active anywhere in the region, which is worth noting during a heat event of this size, because heat and ozone usually travel together. If that changes through the afternoon, airnow.gov is the place it will show first.

The health risk today is the heat itself. Heat illness builds quietly, and the early signs are the ones people talk themselves out of: heavy sweating, cramps, weakness, nausea, headache, cool and clammy skin. That is heat exhaustion, and the response is to move somewhere cool, loosen clothing, sip water, and use cool cloths. Heat stroke is the step past it and looks different: hot skin, confusion, slurred speech, and often no sweating at all. The National Weather Service instruction on today's warnings treats heat stroke as a 911 call.

The people most exposed are older adults, infants, anyone working outdoors, anyone without working air conditioning, and anyone whose medication affects how their body handles heat. A phone call to a neighbor in that group is the highest value thing most households can do today.

The Centers for Disease Control and Prevention Health Alert Network archive index could not be read again this morning, so we are not able to confirm either way whether a new national health advisory has posted. The most recent notice we could open directly was issued August 11 and is written for clinicians rather than households. If you want to check for yourself, the archive lives at emergency.cdc.gov/han.

The heat is the forecast. Extreme heat warnings in the Coachella Valley, Imperial Valley, and the Colorado River corridor run through Friday evening, and the Bay Area and Central Valley advisories run through Thursday night. This is a multi day event, not an afternoon.

Two second order effects are worth planning for. The first is electricity demand. Sustained heat across California, Arizona, and Nevada at the same time is the condition under which grid operators ask for conservation, usually in the late afternoon and early evening when solar output falls and air conditioning load stays high. Pre cooling a home in the morning and easing off between 4 and 9 PM is both the cheapest way to run a house in this pattern and the most useful thing a household can do for the grid.

The second is fire. Heat plus dry fuels is the setup, and the U.S. Drought Monitor recorded moderate drought expanding across northern California on hot, dry conditions in its most recent map. There are no red flag warnings in California today, but late September and October are when offshore wind events begin, and that is the combination that matters here.

For Hawaii, the Central Pacific season runs through November. Lowell is the reminder that the season is real. The week after a storm is the best time to restock what you used and write down what you wished you had, while it is fresh.