National Weather Service United States Department of Commerce


A Historical Study of Tropical Storms and Hurricanes that have affected Southwest Louisiana and Southeast Texas (continued)



Origins of the Tropical Cyclones

Of the tropical cyclones that have affected the designated area in Louisiana and Texas, 38 originated in the Gulf of Mexico, 16 in the Caribbean Sea, 15 in the Atlantic, and 2 in the East Pacific Ocean. The earliest storm to arrive in the region was on May 30th in 1959 (Arlene) and the latest storm affected the area on October 28th (Juan) since 1886.

In May and June, the region of genesis was the Gulf of Mexico (Figure 2). When systems form in the Gulf of Mexico, half move in from the southeast and the other half from due south; either way, areas around Lake Charles may only have a couple days to prepare for the impending storm. Even worse, many of the storms in the survey were intensifying rapidly as they made landfall, such as Audrey in 1957. This makes preparation at the start of the hurricane season not only a good idea, but a necessity. A storm forms in the Gulf to affect the region about once every 16 years in the May 30-June 30 time frame.

By July and August, formation spread into the Caribbean, Southwest and Central Atlantic. This normally gives the region 4 to 5 days to prepare. A storm affected the region, on average, once every 14 years in July and once every 8 years in August; most storms moved in from the southeast.

In September, development across the basin is fairly evenly split between the Atlantic and Gulf of Mexico, while the Caribbean lagged behind. Storms moved in from the southeast and south; one storm affected the area about every 4 years.

In October, the favored area of genesis shifted back to the Western Caribbean, with the Gulf of Mexico and Eastern Pacific lagging behind (both storms that formed in the Eastern Pacific to move into the Gulf of Mexico occurred during October). This would give the region 3 days to prepare for the system in question. Storms moved in almost exclusively from due south during the month and moved into the area once every 11 years.

Only four cyclones of the 71 formed in the Atlantic north of the 20th parallel, two of which formed north of the 30th parallel. One of the tropical cyclones that entered Louisiana initially made landfall in Georgia and moved westward through the Southeastern U.S. just inland from the Gulf coast, never fully emerging into the Gulf of Mexico. This fact means that even though a brewing storm may seem far away off the Carolina coast, there remains a remote possibility that it may yet affect the Northwestern Gulf Coast. This shows you why it is important to take a good look and pay close attention to systems most anywhere in the Atlantic basin; they may eventually become a real threat to the Louisiana and Texas shoreline.

Date of Storm Entrance

The time period from May 21st through October 31st was divided up into periods of 10 or 11 days, depending upon the length of the month. Despite May, July, and October having 31 days, it was pleasing to see no glaring effects of the 11 day periods on the tropical cyclone distribution.

There appears to be one major peak in tropical storm activity during the traditional peak of the hurricane season (September 11-20) and two smaller peaks in mid to late June and in early August. Figure 3 shows how dangerous September can be for the area of study. In hurricane activity, there appears to be a small early season peak in late June and early July, and then the major peak occurs in August and early September, skewed just left of the tropical storm peak.

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