PHOENIX — The battered remnants of Hurricane Polo swept across the U.S. Southwest on Tuesday, dumping more rain on ground already saturated by storms, flooding roadways and forcing residents of small New Mexico towns to abandon their homes over fears that a dam could fail.
Polo struck the Mexican state of Baja California Sur on Tuesday morning with maximum sustained winds of 110 mph (177 kph), then crossed the Gulf of California and weakened to a tropical storm as it tracked inland to the northeast. By Tuesday evening, its circulation was weakening further over northwestern Mexico, but the moisture it carried remained potent well north of the border.
The storm's outer rainbands continued to sweep across the Southwest long after the strongest winds had eased. Desert rivers surged, and arroyos — stream channels that are typically bone dry for much of the year — ran with floodwater, turning normally forgiving desert landscape into a series of fast-moving channels.
In New Mexico, the danger was immediate enough to trigger mandatory departures. Residents in several small towns were told to evacuate, with officials citing concern that a dam in the region could be overtopped or fail. The decision to clear whole communities on short notice reflects how quickly conditions can deteriorate in desert watersheds, where a dam failure or a flash flood can send a wall of water through a town with little warning.
State transportation officials painted a grim picture of the infrastructure damage. By Tuesday evening, the New Mexico Department of Transportation reported flooded roads and debris across the state's highway system, conditions that strangled traffic and cut off access to communities already dealing with rising water.
Arizona, meanwhile, took the heaviest drenching. Parts of the state were soaked, prompting several water rescues in a matter of hours. Rescuers pulled people from swollen washes, low-water crossings and roads that had become impassable, underscoring the danger of attempting to drive through moving water even in areas that look deceptively shallow.
None of this came out of nowhere. Storms had already rolled through parts of the U.S. Southwest overnight Monday, and their effect lingered: the ground was left saturated, and saturated soil absorbs rainfall less efficiently. Once the top layer of earth is full, additional water runs straight off the landscape, which can make subsequent flooding more severe and more sudden.
The timing of that Tuesday rainfall was especially consequential because it landed on top of Monday's soaking. Forecasters had effectively been describing a compounding flood threat, and the pattern of one wet night followed by a second, heavier day is what turns isolated incidents into a regional emergency.
The forecast does not end with the Southwest. Later in the week, the National Weather Service expects the flood risk to shift into parts of the central United States, with heavy rain beginning in Texas and Oklahoma on Tuesday night. The same moisture axis that soaked desert towns is expected to keep moving east, raising the prospect of river swelling and localized flooding far from the storm's center.
The broader hurricane picture has also been unusual this season. A satellite image captured last week showed Tropical Storm Nolo south of Hawaii, Hurricane Odalys in the middle of the Pacific and Hurricane Polo near the Mexican coast — an active eastern and central Pacific even as the Atlantic stayed comparatively quiet. Associated Press reporting has linked that pattern to El Niño, which tends to shift tropical activity toward the Pacific basin.
The contrast matters for Southwest residents, because Pacific storms that strike Baja California and draw moisture north can deliver their worst effects to U.S. communities long after the strongest winds have dissipated inland. A Category-plus hurricane at landfall can degrade into a tropical storm over rugged Mexican terrain and still unleash dangerous rainfall across Arizona and New Mexico.
Recovery will be as messy as the flooding. An Associated Press photograph from Puerto San Carlos, Baja California Sur, showed a man carrying belongings through floodwater past downed electric lines the day after the storm passed, an image of the everyday damage — spoiled possessions, interrupted power and contaminated streets — that follows the water.
For officials, the priority now is moving quickly between hazards: keeping people out of flooded lowlands and washes, checking dam and levee conditions, and clearing debris from highways so that isolated residents can be reached. Small towns evacuated on Tuesday may be the ones that most urgently need to be inspected once the rain moves on.
Forecasters cautioned that the water will take time to recede. Even after the rainbands push east, swollen desert rivers and arroyos can remain hazardous, and roads that appear passable in daylight may be undermined beneath the surface.
For now, residents of the Southwest are absorbing the second punch of a storm that peaked far to the south. Polo's landfall in Baja California Sur delivered the wind; the Southwest, still recovering from Monday's storms, is absorbing the water.
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