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

Wednesday, September 12, 2007

La Niña On Her Way?

The odds of a busy 2007 hurricane season just went up because the water temperature in the Pacific Ocean just went down. That drop in sea surface temperature marks the likely return of La Niña, and an expected increase in stress levels for residents in Florida and other parts of the United States coastline threatened by hurricanes.

Scientists at the Climate Prediction Center announced that La Niña is on its way. “While we can’t officially call it a La Niña yet, we expect that this pattern will continue to develop during the next three months, meeting the NOAA definition for a La Niña event later this year,” said Mike Halpert, acting deputy director of the Climate Prediction Center in Camp Springs, Md.

La Niña conditions occur when ocean surface temperatures in the central and east-central equatorial Pacific become cooler than average. These changes affect tropical rainfall patterns and atmospheric winds over the Pacific Ocean, which influence the patterns of rainfall and temperatures in many areas worldwide.

“La Niña events sometimes follow on the heels of El Niño conditions,” said Vernon Kousky, research meteorologist at the Climate Prediction Center. “It is a naturally occurring phenomenon that can last up to three years. La Niña episodes tend to develop during March-June, reach peak intensity during December-February, and then weaken during the following March-May”.

While past La Nina’s have been responsible for serious droughts in the western United States, it is La Nina’s influence on hurricanes in the Atlantic Ocean and, in particular, the current hurricane season that has caught the attention of local officials.

“Although other scientific factors affect the frequency of hurricanes, there tends to be a greater-than-normal number of Atlantic hurricanes and fewer-than-normal number of eastern Pacific hurricanes during La Niña events,” said retired NOAA administrator Conrad Lautenbacher.

A 1999 study on La Nina’ influence on Atlantic hurricane activity found that “the odds are significantly higher that the U.S. will experience greater (hurricane) impacts because of a larger number of tropical cyclones and higher intensities for each storm.”

The last La Nina lasted from 1998 to 2000, a period that saw 37 tropical storms and 26 hurricanes in the tropical Atlantic. Among the memorable storms during those years were Hurricane Georges that hit the Florida Keys, Hurricane Floyd that threatened Florida and Hurricane Irene that swept across South Florida.

Dr. William Gray’s team at Colorado State University recently updated their hurricane forecast for the remainder of the season. Gray thinks the next few months will be active forecasting 10 named storms, 6 hurricanes and three major hurricanes.

This latest news regarding the developing la Nina will not sit well with residents in Florida, the northern Gulf Coast states and other locales still recovering from the active hurricane seasons of 2004 and 2005. And, while everyone received a nice break from Mother Nature last year, it appears more and more likely that the 2007 hurricane season will be busy.

All because the water temperature is going down.

Posted at 11:36 AM

Wednesday, September 05, 2007

Warning Residents With Unconventional Means

It may seem hard to believe, given our recent hurricane history, but there was a time, not that long ago, when a hurricane was a rare event. In the 1970's, '80's and early 1990's, a hurricane would come along only four or five times a year, often in the safe, far reaches of the tropical Atlantic Ocean.

Since 1995, however, hurricanes have become the rule, not the exception.

The National Hurricane Center reports that the 12 years since 1995 has seen more hurricanes than any other 12 year period in recorded history.

We had our share of those storms in 2004 and 2005 as Charley, Frances, Ivan, Jeanne and Wilma all slammed into the Sunshine State. The 2005 season was worse as a seemingly endless string of tropical storms and hurricanes threatened the United States.

At the top of that list, of course, were Rita and Katrina. Folks in Texas and southwest Louisiana are still recovering from the powerful storms.

The National Weather Service calls Katrina the "most destructive hurricane to ever strike" the United States. Estimates from the insurance industry topped $60 billion in insured losses from Katrina. NOAA says the storm "could cost the Gulf Coast states as much as an additional $120 billion."

The experts who study tropical cyclone patterns and activity say this current period of above-average hurricane activity is likely to continue, perhaps for many more years. The scientists say these above-average periods run in cycles and our current cycle may last another 10 to 20 years.

With so many potential hurricanes looming in our future, helping people prepare for the storm and knowing how to react is quite a challenge for the men and women of the National Weather Service. In August of 2004, forecasters at the National Weather Service Melbourne, Florida office met that challenge head on as Hurricane Charley bore down on central Florida.

Charley, a small, but powerful Category 4 hurricane, had slammed into Florida's southwest coast on the morning of August 13, 2005. Hours after striking Charlotte Harbor, Charley remained a destructive and powerful hurricane as it headed for the Orlando-metro area with sustained winds topping 100 mph.

Forecasters at the Melbourne weather office feared that an update on Charley's dangerous wind conditions would get lost in the dozens of weather bulletins already issued from their office and the National Hurricane Center. Their solution was simple, yet brilliant: they put out a tornado warning.

"We ended up using a wrench for a hammer," said Dennis Decker, the warning Coordination Meteorologist with the Melbourne office.

There was no tornado but the tornado warning got the attention of all the television and radio stations in the Orlando area. The tornado warning allowed the National Weather Service to get the word out quickly that Charley's 100 mph winds were about 30 minutes away.

"When you do something outside of the box like that, you wonder how the people up the chain of command in the Weather Service are going to react," said Decker. "They basically confirmed that it was a good idea."

One of the lessons from the 2004 Hurricane season was that you don't have to be on the coastline to be affected by the winds of a hurricane. As residents of Orlando discovered during Hurricane Charley, these monster storms can affect even the areas that many people head to, when evacuated from the coast. That presents a unique challenge to forecasters at the Weather Service, and that may require even more thinking outside the box.

Posted at 8:00 AM