Hurricane Polo strengthened into a Category 5 hurricane early Tuesday, Sept. 22, with maximum sustained winds near 160 mph (260 km/h). In National Hurricane Center Intermediate Advisory 7A, issued at 6 a.m. CST, forecasters placed Polo about 220 miles (355 kilometers) south of Zihuatanejo and about 360 miles south-southeast of Manzanillo, with an estimated central pressure of 926 millibars. Polo was moving east near 6 mph and is expected to make a sharp turn toward the northwest and west-northwest Tuesday night and Wednesday.

That turn matters most for the coast. On the forecast track, the NHC expects Polo's core to be near the coast of southwestern Mexico over the next few days while remaining offshore. A Tropical Storm Watch covers the shoreline from Tecpan de Galeana in Guerrero to Manzanillo in Colima, after Mexico's government extended the watch northward to Manzanillo Monday night. The NHC said additional watches or warnings could be needed Tuesday.

For residents and visitors in Ixtapa-Zihuatanejo, Lázaro Cárdenas and Manzanillo, the current forecast points to flooding rain, mudslides and dangerous surf rather than a direct landfall. Farther north, New Mexico and parts of far West Texas face a separate flood threat this week as deep moisture streams into the Southwest.

From Tropical Storm to Category 5 in About a Day and a Half

The system became Tropical Depression Seventeen-E at 3 p.m. CST on Sunday, Sept. 20, and was upgraded to Tropical Storm Polo with 40 mph winds at 9 p.m. CST that evening. It became a hurricane by midday Monday, reached 85 mph by 3 p.m. CST and 110 mph by 9 p.m. CST. By 3 a.m. CST Tuesday, it was a 150 mph Category 4 hurricane, and three hours later it crossed the Category 5 threshold.

That is a gain of 120 mph in roughly 33 hours between the advisory that named Polo and the one that declared it a Category 5. In NHC Discussion 7, issued at 3 a.m. CST, forecasters said Polo had strengthened by about 90 knots (about 105 mph) over the previous 24 hours, a rate they called "truly remarkable." The standard benchmark for rapid intensification is an increase of about 35 mph in 24 hours. The San Francisco Chronicle reported that Polo's climb from tropical storm to Category 5 appears to be the fastest on record in the eastern Pacific, though that timeline is preliminary and could change during the NHC's post-season review.

"Polo continues to intensify at a very rapid rate," forecasters wrote in the same discussion. They described a compact, well-defined eye surrounded by an intense eyewall. The discussion cautioned that internal changes in powerful hurricanes often cause intensity to rise and fall. It also forecast slow weakening later in the period as easterly wind shear increases slightly, although Polo is expected to remain a major hurricane throughout the five-day forecast.

The warning signs appeared early. On Monday, NHC forecaster Eric Blake wrote that a key rapid intensification index was showing percentages "as high as I have ever seen them," Yale Climate Connections reported.

Polo remains relatively compact but is growing. Hurricane-force winds now extend up to 35 miles (55 kilometers) from the center, and tropical-storm-force winds reach up to 90 miles (150 kilometers). Monday night's advisory put those figures at 30 and 80 miles. NOAA Hurricane Hunters were scheduled to investigate the storm later Tuesday, which should sharpen the intensity estimate.

Rain, Surf and Track Risks for Guerrero, Michoacán and Colima

The NHC forecasts 4 to 8 inches (100 to 200 millimeters) of rain across coastal Guerrero and Michoacán through Thursday, with isolated totals up to 12 inches (300 millimeters). Coastal Oaxaca, Colima and Jalisco could see 3 to 6 inches (75 to 150 millimeters).

The NHC warned that this rain may cause life-threatening flooding and mudslides, especially in steep terrain. The Sierra Madre del Sur rises sharply behind much of this coastline, so runoff reaches river valleys, hillside neighborhoods and coastal roads quickly. Tropical storm conditions are possible within the watch area by early Wednesday.

Swells generated by Polo are expected to reach parts of southwestern Mexico over the next few days and are likely to cause life-threatening surf and rip currents. Beachgoers, surfers and small-boat fishermen face the most immediate risk, even when skies look calm.

Confidence in the track is limited. Discussion 7 said there is still considerable uncertainty about how close the hurricane will get to the coast, and that some wind, rain and surf impacts appear likely at its closest approach. Polo should begin pulling away Thursday night and Friday. Over the weekend, steering currents become more complicated as Polo nears Tropical Storm Odalys to its west, which should slow the hurricane. "Some computer forecasts show Odalys interacting with Polo in some fashion in several days," hurricane specialist Bryan Norcross told Fox Weather. A small shift toward the coast would raise wind, rain and surf risks along a longer stretch of shoreline, so readers should look at the full forecast cone rather than only the center line.

Southwest Flood Watches and the Next 48 Hours

Several National Weather Service offices have flood watches in effect for much of New Mexico and parts of far West Texas, including the El Paso area, from Tuesday afternoon into Wednesday. The National Weather Service in Albuquerque described a dangerous surge of monsoon moisture that will bring widespread heavy rain Tuesday through Thursday, with a good chance of scattered flash flooding and some river and tributary flooding. Neighboring offices said an early-season back door cold front will interact with deep tropical moisture, with the heaviest rain most likely Tuesday night into Wednesday morning.

Fox Weather reported that moisture from Polo is enhancing the threat. NWS forecast discussions describe a broader setup that also includes the cold front and a Pacific low, so the event should not be attributed to Polo alone.

The timing is sensitive. Fox Weather noted that the watches come about a week after flooding enhanced by a different tropical disturbance killed three people near Newcomb, New Mexico. Burn scars, dry washes, low-water crossings and poorly drained streets carry the greatest risk.

In Mexico, residents should follow instructions from the Servicio Meteorológico Nacional and state civil protection agencies, which issue local warnings and make evacuation decisions. Travelers should confirm flights and lodging directly and stay off beaches during high surf. In New Mexico and West Texas, never drive into water covering a road, and move to higher ground immediately if a Flash Flood Warning is issued for your area.

Nature World News previously reported on Polo's rapid intensification and the 12-inch rain forecast, which was based on Advisory 5, when Polo was an 85 mph hurricane. Since then, its winds have nearly doubled, and the watch has been extended to Manzanillo.

The NHC's next complete advisory was scheduled for 9 a.m. CST (11 a.m. EDT) Tuesday, with intermediate advisories every three hours while watches are in effect. Polo now sits at the top of the Saffir-Simpson scale, but its core is forecast to stay at sea. The biggest unknowns are how close it tracks to the coast midweek and how Odalys shapes its path this weekend.

Developing Story Timeline

Sept. 22, 6 a.m. CST: Polo reaches Category 5 with 160 mph winds, according to NHC Intermediate Advisory 7A.

Sept. 22, 3 a.m. CST: Polo is a 150 mph Category 4 hurricane in NHC Discussion 7.

Sept. 21, 9 p.m. CST: Winds reach 110 mph, and Mexico extends the Tropical Storm Watch to Manzanillo.

Sept. 21, 3 p.m. CST: Polo is an 85 mph hurricane in Advisory 5, the basis of Nature World News' earlier report.

Sept. 20, 9 p.m. CST: The depression becomes Tropical Storm Polo with 40 mph winds.

Sept. 20, 3 p.m. CST: Tropical Depression Seventeen-E forms off southwestern Mexico.

What Readers Want to Know

How strong is Hurricane Polo right now?

As of NHC Intermediate Advisory 7A at 6 a.m. CST on Sept. 22, Polo had maximum sustained winds near 160 mph, which makes it a Category 5 hurricane. The NHC said some additional strengthening is likely through Tuesday night, with fluctuations possible Wednesday.

Will Polo make landfall in Mexico?

The NHC forecasts Polo's core to stay near the coast of southwestern Mexico but offshore over the next few days. Forecasters said there is still considerable uncertainty about how close it will get, and some wind, rain, and surf impacts appear likely.

Which parts of the coast are under a watch?

A Tropical Storm Watch covers the coast from Tecpan de Galeana to Manzanillo. The NHC said additional watches or warnings could be needed Tuesday.

How much rain is forecast?

The NHC forecasts 4 to 8 inches of rain across coastal Guerrero and Michoacán through Thursday, with isolated totals up to 12 inches. Coastal Oaxaca, Colima and Jalisco could see 3 to 6 inches.

Is Polo affecting the United States?

Polo's winds are not a U.S. threat. NWS flood watches cover much of New Mexico and parts of far West Texas as monsoon and tropical moisture meet a cold front, and Fox Weather reports that Polo's moisture is contributing.

What should travelers to Zihuatanejo or Manzanillo do?

Check directly with your airline and hotel, and follow instructions from Mexican authorities. Stay off beaches during high surf, and avoid driving through floodwater.

When is the next update?

The NHC issues complete advisories at 3 a.m., 9 a.m., 3 p.m., and 9 p.m. CST, with intermediate advisories in between while watches are in effect.