Monday, September 24, 2007

How Did Humberto Get So Strong?

It wasn’t supposed to be a big deal. When Tropical Storm Humberto took aim at the upper Texas coast last week forecasters were predicting periods of rain and blustery winds. Flooding was the primary concern with rainfall totals approaching ten inches expected in some areas. For folks who had gone through Hurricane Rita in 2005, Humberto was expected to be a walk in the park.

Yet, while residents of High Island and other Texas coastal communities slept, Humberto was changing, intensifying from a run-of-the-mill tropical depression into a category one hurricane. At 2 AM on September 13, Humberto made landfall with winds of 85 mph.

Humberto’s rapid intensification-from tropical depression to hurricane in 16 hours-surprised everyone, from the residents of Texas to the forecasters at the National Hurricane Center.

"To put this development in perspective, no tropical cyclone in the historical record has ever reached this intensity at a faster rate near landfall,” said National Hurricane Center senior hurricane specialist James Franklin. “It would be nice to know, someday, why this happened."

Someday, Franklin and other scientists may figure out why Humberto strengthened so quickly. Someday, researchers will know why Felix grew from a tropical storm to a category five hurricane in 51 hours earlier this year, or why Wilma exploded from a tropical storm to a category 5 hurricane in 24 hours.

Someday they will find the answer to rapid intensification of tropical cyclones but, for now, the process remains a mystery. And, a big concern for government officials anywhere a hurricane may make landfall. Craig Fugate, director of the Florida Division of Emergency management, says that his team always prepares for a storm that is one notch up from what is predicted.

While very warm water and low wind shear probably helped with the storm’s rapid intensification, the exact reasons why Humberto went from a depression to a hurricane in such a short period of time remains a mystery. Solving that mystery is the number one priority of the hurricane research community.

“While I was the Director of the National Hurricane Center, I can say that every talk that I gave at local, state and national hurricane conferences mentioned the concern over rapid intensification,” said Max Mayfield, former director of the Hurricane Center.

Back in June, forecasters at the National Hurricane Center began using a new computer model that eventually may help with the rapid intensification issue. Called “one of the most dynamic tools” for hurricane forecasters, the Hurricane Weather and Research Forecast Model (nicknamed HWRF) utilizes advanced physics of the atmosphere, ocean and waves to predict the future track and intensity of tropical cyclones.

“Over the next several years, this model promises to improve forecasts for tropical cyclone intensity, wave and storm surge, and hurricane-related inland flooding,” said Mary Glackin of the National Weather Service. “It will be one of the most dynamic tools available for our forecasters.”

Still, neither the HWRF nor any of the other hurricane models, predicted the rapid intensification of Humberto. In fact, it is fair to say that no one saw it coming.

Back in the first half of the 20th century-before orbiting satellites, long-range radars and the much talked about computer models-hurricanes really did sneak up on people. Other than a few random ship reports residents of coastal areas had no idea a hurricane was headed their way until the wind and rain swept across the coastline.

Today, we all know when a storm is about to strike, but until the rapid intensification mystery is solved, sometimes hurricanes will be full of surprises.

Posted at 11:42 AM