Average lead time for storms in the area of study

Data from the 71 storms were examined in greater detail to determine average motion prior to landfall, specifically while in the Gulf of Mexico. The most common direction for a storm to originate from was the southeast with 13 storms entering from that region. The storms moved fastest from the southwest, as they were being picked up by the mid-latitude westerlies; average motion was 12 m.p.h.. Storms moved slowest from the east, where the average motion was about 9 m.p.h.. Figure 4 was produced with an average motion of 8.9 knots (10.2 m.p.h.) in mind; this was the average motion of all the storms in the sample.

Note that the radials are labeled in hours, not nautical miles; each radial is equal to about 214 nautical miles. This was done to give the reader some rough estimate, at a glance, of how long it would take a "typical storm" to move to Lake Charles, LA. Storms that form in the Gulf do not give much advance notice prior to landfall. Storms start adversely affecting the area as much as 24 hours before landfall.

It is worth pointing out that storms over the southern Gulf of Mexico (Bay of Campeche) can meander for days. This is because sometimes the Mexican Plateau seems to divert the steering winds for tropical cyclones to the north, causing some storms to stall for days due to weak winds in their vicinity; recent examples include Opal and Roxanne from the 1995 season. Most of these storms, however, either move into Mexico or eventually accelerate off to the northeast, leaving the studied area in the clear.

Possible effects of ENSO (El Niño/Southern Oscillation)

A list of the years of moderate to strong warm ENSO events were collected to check on any possible relationship with tropical cyclone entrance into Louisiana and Southeast Texas. These warm events seemed to have no significant correlation to an increase or decrease in tropical storms and hurricanes entering the area; it has been recently discovered though that it does make a difference further down the Texas coast.

Unexpectedly, warm events seemed to have a strong correlation to major hurricanes in this area. Five of the eight major hurricanes struck the region during the middle of moderate to strong El Niño events. If one expands the criteria to within one year of a moderate ENSO, seven of eight become included. Further study is needed to totally resolve this mystery.

Dry Mays as a specter to the coming season

The Warning and Coordination Meteorologist (WCM) down in the Miami Weather Office, Jim Lushine, did an informal study a few years back to determine whether or not dry Mays had any correlation with major hurricanes entering an area, in his case South Florida. In South Florida, this may infer a shift in the normal position of the Azores-Bermuda High over the Florida peninsula, which may foretell a surface trajectory from the deep tropics favorable for hurricane landfalls later in the year. Looking at the major hurricane landfalls, and then comparing it to May rainfall from years past, this does not appear to be a factor in the Lake Charles area.

Definitions

The following is a list of definitions of terms used in this paper:

Tropical Cyclone - A low pressure system which develops over warm ocean surfaces and has a warm core, has a closed surface circulation, and maximum sustained one-minute winds of 34 knots (39 mph/17 m/s) or greater.

CWA - County warning area; area in which a National Weather Service Forecast Office issues forecasts and warnings. For Lake Charles, this includes 17 parishes in Louisiana and six counties in Southeast Texas

Tropical Storm - A tropical cyclone with maximum sustained one-minute winds of less than 64 knots (74 mph or 37 m/s).

Hurricane - Tropical cyclone with maximum sustained winds of 64 knots (74 mph or 37 m/s) or greater. These storms generate life-threatening storm surges.

Major hurricane - Hurricanes with maximum sustained one-minute winds of 100 knots (115 mph or 58 m/s) or greater. In addition to high storm surges, these storms can create catastrophic damage from extremely high winds.

Saffir-Simpson Scale - Has categories of 1 through 5 to rate maximum sustained one-minute winds, central pressure, and storm surge to a hurricane's related damage. Five is the highest category with winds in excess of 130 knots (155 mph or 78 m/s). In the Western Pacific Ocean, category 5 hurricanes are also known as super typhoons.

El Niño/Southern Oscillation (ENSO) - Global climatic shifts associated with, and in the case of El Niño, significant warming of the waters of the eastern Pacific Ocean west of Peru about once every 5 to 7 years. Amongst the global consequences of El Niño (warm ENSO events) include suppressed tropical cyclone activity in the Atlantic basin, floods along the West Coast of the United States, and droughts in Australia and Indonesia. During La Niñas or El Viejos (cold ENSO events), the reverse is true.

Acknowledgments

The author wishes to thank Steve Rinard at the NWS office in Lake Charles along with Mike Kosiara and Paul Trotter at the NWS office in Slidell, and James Lushine of the NWS office in Miami for their input in the paper. The El Niño correlation would not have been established if not for Ricardo Correa-Torres of Florida State University providing information on years of previous moderate and strong El Niño/warm ENSO events.

Bibliography

Hebert, Paul J., Jerry D. Jarrell, Max Mayfield: The Deadliest, Costliest, and Most Intense Hurricanes of This Century (And Other Frequently Asked Hurricane Facts), National Oceanic And Atmospheric Administration, NOAA Technical Memorandum NWS NHC-31, 1995.

Kelly, Joseph T., Alice R. Kelley, Orrin J. Pilkey, Sr., Albert A. Clark: Living with the Louisiana Shore. Duke University Press: Durham, 1984.

Newmann, C.J., B.R. Jarvinen, A.C. Pike, 1987: Tropical Cyclones of the North Atlantic Ocean 1871-1992 (plus inserts to 1997), National Climatic Data Center, Historical Climatology Series 6-2, 186 pp.

Rasmusson, Eugene M., Thomas Carpenter: "Variations in Tropical Sea Surface Temperature And Surface Wind Fields Associated With the Southern Oscillation/El Niño," Monthly Weather Review, 1982. 110:354-384.

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