Major Hurricane Roslyn is heading for the west coast of Mexico and is expected to roar ashore at or near Category 3 strength somewhere in the states of Jalisco or Nayarit late Saturday or early Sunday. The National Hurricane Center warns that “preparations … should be rushed to completion” for those within Roslyn’s path, the agency sounding the alarm for expected “damaging winds, a dangerous storm surge … [and] heavy rainfall [that] could lead to flash flooding and mudslides.”
Hurricane warnings are in effect from Playa Perula to El Roblito, including Puerto Vallarta, a popular vacation destination. Las Islas Marías, a spattering of islands off the coast, also are in the warning zone. To the north of the warning zone, a hurricane watch stretches all the way to Mazatlan, while tropical storm watches cover that area and the zone south of the hurricane warning to Manzanillo.
There are increasing odds that the storm could come ashore as the strongest to strike that region since the 2002 storm Kenna, which made landfall at the mouth of the Rio Grande de Santiago near Boca de Asadero as a Category 4 hurricane with 140 mph winds. It had been a Category 5 storm just 10 hours before landfall.
Roslyn’s rapid intensification
Roslyn emerged after a group of thunderstorms off the west coast of Mexico congealed into a tropical depression and eventually a named storm on Thursday. It wasn’t until 11 p.m. Eastern time Friday that Rosslyn became a hurricane, but it rapidly intensified into a major hurricane, defined as Category 3 or higher, on Saturday morning, just six hours later.
Rapid intensification, defined as a spike of 35 mph or more in a storm’s maximum sustained winds within 24 hours, is more likely in the presence of warmer waters and calm upper-level winds. There are emerging links between human-induced climate change and the frequency and severity of rapid intensification.
By late morning Eastern time Saturday, Roslyn had winds of 130 mph — low end Category intensity and was a little more than 150 miles southwest of Manzanillo, Mexico. At the time, it was moving northwest at 7 mph, but it was beginning a curve to the north-northeast. It will be steered into the western coastline of Mexico as it begins to feel the effects of an approaching shortwave trough, or pocket of cold air, low pressure and spin aloft, near the Baja Peninsula.
Roslyn’s expected effect
On its present course, Roslyn looks to make landfall in the same area that Kenna did. That would place rural areas in coastal Narayit in line to experience the eyewall, or ring of furious winds surrounding the calm eye. Although Roslyn will be gradually weakening, winds gusting near 120 mph are still possible at the immediate shoreline. Communities including San Blás, Matenchén and Aticama may experience the strongest winds. Winds will drop off exponentially outside of the eyewall, but tropical-storm-force buffets are still possible as far south as Puerto Vallarta.
The greatest surge will occur just south of where Roslyn’s center makes landfall. That’s because the storm, like all large-scale low-pressure systems in the Northern Hemisphere, is spinning counterclockwise; that means winds south of the eye will be aimed onshore. That will efficiently push water toward the coastline.
The National Hurricane Center writes that “a dangerous storm surge is expected to produce significant coastal flooding near and to the east of where the center makes landfall.”
The agency also warns of “large, destructive waves” near the coast, which computer models indicate could approach 25 feet in height.
Storm surge risk is generally less on Mexico’s west coast than on its Gulf Coast because the slope of the continental shelf is more abrupt on the west coast. Without the aid of the gently sloping seabed that exists in the gulf, a storm on the Pacific side is less able to push large volumes water on to the coastline.
The storm also is forecast to produce 4 to 6 inches of rain, with maximum totals of around 8 inches, along the upper coast of Colima, Jalisco, southeastern Sinaloa and western Nayarit, including Las Islas Marías.
“This rainfall could lead to flash flooding and landslides in areas of rugged terrain,” the Hurricane Center wrote.