Isaias strengthened into a major hurricane Friday as it headed toward the U.S. Gulf Coast, where final preparations were underway for potentially life-threatening storm surges and high winds.
Meanwhile, Hurricane Simon was headed toward Mexico's Pacific coast and strengthened into a Category 2 storm late Friday morning. U.S. forecasters issued a hurricane warning for parts of the central and southwest coast, where hurricane-force winds were expected within 36 hours.
Tropical storm activity has been above average this season in the Pacific because of a strong El Niño, a natural, temporary warming of parts of the Pacific that warps weather worldwide. In the Atlantic, El Niño's decapitating winds and the Gulf of Mexico's toasty, storm-fueling waters are battling over Isaias's future strength.
Lifeguards clear Florida's Pensacola Beach
Double red flag warnings prohibiting swimming and wading were posted Friday morning as beachgoers were asked to evacuate. The surf was at about 6 feet (2 meters) and rising, officials said in a social media post.
Lifeguards were expected to leave the beach mid-morning after urging people to leave and stay safe during the storm.
"Bottom line is to just please be smart. Please be smart," Pensacola Mayor D.C. Reeves said in a social media post. "You wouldn't consciously put your lives in danger. Make sure that you don't put the fire, the police — please do not put them in danger. They are not going to be able to respond."
Reeves warned that bridges may be closed as conditions worsen.
Simon headed twoards Mexico's Pacific coast
The center said maximum sustained winds have increased to nearly 100 mph (155 kph), and that Simon, which was headed toward part of Mexico's Pacific coast, is expected to continue strengthening rapidly during the next day or so. Simon is forecast to become a major hurricane by late Friday and strengthen further on Saturday.
U.S. forecasters earlier issued a hurricane warning for parts of the central and southwest coast, where hurricane-force winds were expected within 36 hours.
Weaker wind shear during El Niño plays a role in the formation of Isaias in the US Gulf
The super El Niño has been a nonstop machine cranking out tropical storms that have seemingly rolled through the Pacific region like rush-hour traffic. Now, it's the U.S. Gulf Coast's turn.
Isaias is the ninth named storm of the season. None of the previous ones reached hurricane strength. A normal hurricane season has 14 named storms, seven becoming hurricanes and three reaching major hurricane level, which is more than 110 mph (177 kph).
"The season has been completely dead — and we're still going to have an impactful storm hitting the northern Gulf," Colorado State University hurricane expert Phil Klotzbach said Wednesday. "How impactful it is remains to be seen."
El Niño involves a natural, temporary warming of parts of the equatorial Pacific, setting off a chain of unusual weather around much of the world. While it's one of many factors in play in the formation of Isaias, the current El Niño "still is certainly driving the bus," Klotzbach said.