to full-scale hurricane, surprised the Texas-Louisiana coast with 85-mph (137-kph) winds and heavy rain that knocked out power to more than 100,000 and killed at least one person. Meanwhile, Tropical Storm Ingrid formed late Thursday in the open Atlantic Ocean, but it was far from land.
Meteorologists were at a loss to explain the rapid, 16-hour genesis Thursday of Humberto, the first hurricane to hit the U.S. since 2005.
"Before Humberto developed, you looked at the satellite imagery the day before, and there was virtually nothing there. This really spun up out of thin air, very, very quickly," National Hurricane Center specialist James Franklin said. "We've never had any tropical cyclone go from where Humberto was to where Humberto got."
Surprising as Humberto was, forecasters said it may have been a blessing that it did not linger longer over warm waters of the Gulf of Mexico, which could have given it time to develop into more than a minimal hurricane.
Texas coastal residents prepared for a tropical storm rainmaker that would quickly flood the ground already saturated from the wettest summer in 60 years. Although forecasts called for up to 1 foot (30 centimeters) of rain, Humberto produced no more than half that and generated much more wind. By late afternoon, it had weakened to a tropical depression churning across the southern U.S.
The only reported death was a man who died in southeast Texas when the carport at his home collapsed, police said.
Humberto made landfall less than 50 miles (80 kilometers) from where Hurricane Rita did in 2005, and areas of southwest Louisiana not fully recovered from Rita were bracing for more misery.
About 118,000 customers were out of power in Texas and Louisiana at one point, utility officials said.
Along Port Arthur's refinery row, three plants were idled until power was restored. Some of the plants could be off-line for several days, even after power is restored, because they must undergo the full restart process.
Hurricane center forecasters first mentioned what would become Humberto on Saturday, when it was a disorganized system of showers and thunderstorms stretching from Cuba west over the southern Gulf of Mexico.
In a little more than 14 hours, Humberto went from being a tropical depression to a Category 1 hurricane.
Only three other storms have pulled off a similar feat, growing from depression to hurricane in 18 hours _ Blanche in 1969, Harvey in 1981 and Alberto in 1982 _ but all of them were out at sea at the time, not about to crash ashore like Humberto.
Experts cannot draw conclusions on possible trends of faster-forming hurricanes based on just one storm. Franklin said part of the problem was Humberto was a relatively small-sized storm, making it harder for forecasters and computer models to analyze.
One possibility, he said, is that because Humberto was close to landfall, greater friction between air currents and the ground could have forced winds upward into the storm, lending to its intensification.
Kerry Emanuel, a meteorology professor at the Massachusetts Institute of Technology, said it is not so much the positive factors like warm Gulf of Mexico waters that help fuel storms like Humberto to intensify quickly. It is the lack of negative factors like wind shear that would weaken a storm.
The most destructive natural disaster in U.S. history, 2005's Hurricane Katrina, also developed quickly before its first landfall near Miami. It went from a tropical depression to a hurricane in just over two days before hitting Florida. It leveled parts of the Gulf Coast a few days later, part of the busiest hurricane season ever recorded.
