Louisiana Considered National Hot Spot Says LSU AgCenter Climatologist

John Grymes  |  4/19/2005 10:28:32 PM

News You Can Use For July 2004  

Although Louisiana summers are predictably hot and humid with afternoon thunderstorms, Mother Nature still can throw a curve ball at the Sportsman's Paradise. That curve ball is tropical weather, says LSU AgCenter climatologist Jay Grymes.

As south Louisiana experienced in June 2001 with remnants of Tropical Storm Allison, even a poorly defined tropical event can dump several months' worth of rainfall in as many days.

"Most weather pros agree that coastal Louisiana is one of the nation's hot spots for tropical system landfalls," Grymes says, adding, "That is why residents of Louisiana are so intrigued by hurricanes and tropical storms, and why we wait so intently on hurricane season forecasts."

Experts generally agree that the 2004 Hurricane season will be a busy one, with an above-normal number of storms developing in the Atlantic basin.

Dr. William Gray, professor of atmospheric science at Colorado State University, and who is considered by many as the national authority in hurricane forecasting, currently anticipates 14 named storms, which include tropical storms or storms of hurricane intensity. That figure compares to a long-term average of 10 or fewer per season.

"Unfortunately, Gray and his counterparts are unable to tell us what that means in terms of Gulf of Mexico activity or the potential threat to Louisiana," Grymes says, explaining, "Truth is, it will be decades - if ever - before extended-range hurricane forecasting provides a realistic insight into year-to-year landfall threats."

As a result, Grymes says our next best option is to look at Louisiana's historical trends and use those statistics as our annual wake-up call.

History reveals there is a 2-in-3 chance, on average, of a tropical storm or hurricane making landfall somewhere along the Louisiana coast each hurricane season. Of those landfalls, nearly half were by storms of hurricane strength, with the Bayou State having served as "ground zero" for six major hurricanes (category 3 or higher on the Saffir-Simpson Scale) over the last 60 years.

The Saffir-Simpson Hurricane Scale is a 1-5 rating based on the hurricane's present intensity, according to the National Hurricane Center (http://www.nhc.noaa.gov/aboutsshs.shtml). It is used to estimate the potential property damage and storm-surge flooding expected along the coast from a hurricane landfall.

Statistics indicate that Louisiana is frequently the target of tropical systems, but the arrival of those systems has been anything but regular over the past century. Some years have been more active than others, and a number of hurricane seasons have come and gone without a single "hit."

This year-to-year variability is quite evident over the past six years. The year 1998 saw close-calls by hurricanes Earl and Georges, flooding rains spawned by a distant Frances and a direct hit by T.S. (tropical storm) Hermine. By contrast, 1999 and 2000 were quiet seasons for the Bayou State.

Then came 2001's Allison, a system that was downgraded to a sub-tropical storm before she entered the Bayou State, but her six-day deluge proved to be an all-time record rainstorm for portions of south Louisiana, resulting in widespread flooding and damages estimated at roughly $75 million.

The next season, 2002, proved to be Louisiana's "busiest" season ever, with a record four landfalls. These included near back-to-back hits by Isidore and Lili which resulted in at least $500 million in property damages and millions more in agricultural losses. Even 2003 had its landfall, with T.S. Bill coming ashore along Terrebonne Parish.

Long-term records show that September is Louisiana's peak landfall month, accounting for more than 40 percent of all landfall dates over the 20th Century. But the Bayou State has seen landfalls as early as late May (before the official June 1 start of the hurricane season) and as late as November 1st.

"Obviously, there is no month where we can let our guard down," Grymes points out. He recalls that while the 2003 hurricane season was not unusually active for Louisiana, last year's season reminds us of the overall unpredictable nature of the tropical season: it had an incredibly early start with April's T.S. Ana and an unusual end, with December's Odette and Peter!

What raises the danger level even higher for Louisiana is the state's proximity to the Gulf of Mexico. By June, Gulf water temperatures have climbed above 80 F, and therefore are more than warm enough to fuel a developing storm. As a result, what might start as an unorganized cluster of thunderstorms over the open Gulf could "spin up" into a potentially-dangerous tropical system in a period of less than a day. This is precisely what happened with 1997's Danny, which slammed into Plaquemines Parish in mid-July of that year.

"Take that potential for rapid development and couple it with estimates from the emergency management community that suggest 48-72 hours are required to implement full evacuation of coastal Louisiana, and you quickly see a recipe for loss-of-life," the climatologist says.

The bottom line is that Louisiana residents, particularly those living near the coast and along tidal waterways, need to have a plan of action should the threat materialize. And households should review these plans every season to assure that all members of the family understand the steps to be taken.

For those near the coast, that hurricane action plan includes making provisions for the potential of evacuation should the call go out from emergency management officials. Coastal communities are susceptible to the immediate impacts of damaging winds and storm surge, along with heavy rains and the potential for isolation from inland areas once storm inundation has begun.

"But even those living further inland should consider developing a family response plan," Grymes advises. Although evacuation may be unlikely, inland wind damage and rain-induced flooding can create havoc and leave local infrastructure in disarray for days or even weeks!

For information on related topics, visit the AgCenter Web site at www.lsuagcenter.com. For local information and educational programs, contact an extension agent in your parish LSU AgCenter office.

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On the Internet: LSU AgCenter: http://www.lsuagcenter.com/
On the Internet: National Hurricane Center: http://www.nhc.noaa.gov/aboutsshs.shtml
Source: Jay Grymes (225) 578-6870, or JGrymes@agcenter.lsu.edu 

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