Preliminary Report
Hurricane Florence
07 - 11 September 1988

1988 PRELIMINARY REPORTS

Tropical Storm Alberto (TS)
Tropical Storm Beryl (TS)
Tropical Storm Chris (TS)
Hurricane Debby (1)
Tropical Storm Ernesto (TS)
Hurricane Florence (1)
Hurricane Gilbert (5)
Hurricane Helene (4)
Tropical Storm Isaac (TS)
Hurricane Joan (4)
Tropical Storm Keith

a. Synoptic History

The first eleven days of September were quite active meteorologically over the western Gulf of Mexico. Hurricane Debby passed across the Bay of Campeche from 1 to 2 September and made landfall in Mexico. Tropical Depression Ten formed and made landfall over east Texas/western Louisiana on 3 September, ahead of a cold front which would serve as the catalyst for Florence. The next day, the cold band accompanying the cold front had left the Texas coast and was entirely over the Gulf of Mexico. On 5 September the convective band moved southeastward and was located from Vera Cruz, Mexico to Tampa, Florida. The next day the band remained nearly stationary but began to split over the central Gulf as a frontal wave developed over the northern portion and began moving northeastward. Concurrently, the southern portion began showing signs of tropical organization. The surface pressures associated with the southern portion of the frontal trough were generally low. By 7 September convection had organized a spiral band structure but deep convection was for the most part transitory. A surface circulation appeared to have formed by 0600 UTC, 7 September while centered about 180 nautical miles northwest of Merida, Mexico. Tropical Depression advisories were began at 1600 UTC on that day and at 1800 UTC the depression was upgraded to Tropical Storm Florence when Air Force reconnaissance and satellite imagery analysis estimated that the surface wind speed associate with the system reached 40 mph.

Tropical Storm Florence drifted generally eastward on 7 September, following the remains of the frontal trough and then became stationary the next day as the Atlantic as the Atlantic ridge built strongly northwestward, bringing the frontal remnants. The steering currents were weak during this period but the mean mid to upper level trough position was forcast to remain essentially stationary over the lower Mississippi Valley. Thus on 9 September due to the position of the trough and the strengthening of the Atlantic ridge, the northward movement of Florence began.

The forward speed of Florence averaged 12 mph for the first half of 9 September and 15 mph for the second half, as the system accelerated northward. The maximum intensity of Florence was reached just before landfall at 2300 UTC 9 September with landfall occurring over the western Mississippi Delta 3 hours later. Florence weakened quickly, losing all its deep convection as it passed across New Orleans and over the west half of Lake Pontchartrain. Maximum sustained winds were reduced below tropical storm strength by 1200 UTC 10 September when the system was centered just northwest of Baton Rouge. The remnants of Florence could be followed for one more day to extreme northeast Texas where it could no longer be defined.

b. Meteorological Statistics

Florence was a hurricane for only about 12 hours. The highest surface wind estimated by Air Force reconnaissance was 98 mph at 2310 UTC on 9 September just before landfall. The highest sustained wind near the surface was 81 mph measured on oil platform, MP73 (height unknown), located near 29.3°N 88.9°W at 0511 UTC 10 September. The lowest surface pressure reported by Air Force reconnaissance was 982 mb near the time of landfall. An automatic Coast Guard weather station (8R3) located at the Southwest Pass of the Mississippi Delta reported a surface pressure of 987 mb with a calm wind as the eye of the hurricane passed. The closeness of reliable observations within and surrounding New Orleans, showed that the center of Florence passed quickly over the city and the western portion of Lake Pontchartrain.

1. Storm Surge Data

Highest storm tides were reported at the same time east of New Orleans on the Bayou Benvenue which reached 7.5 feet above Mean Sea Level (MSL) and on the Industrial Canal where the maximum height reached 6.5 feet above MSL. As the storm passed across the western portion of Lake Pontchartrain the high water changed rapidly across the lake from 5 feet about MSL at the West End Marina at 0800 UTC to 4.8 feet above MSL near the north end of the Lake Pontchartrain Causeway at 1200 UTC, 10 September.

In general little to or no wind or storm surge damage occurred along the Mississippi and Alabama Gulf coasts.

2. Rainfall Data

Rainfall amounts were generally light for a hurricane making landfall in southeastern Louisiana. The 24 hour rainfall amounts ending at 1200 UTC, 10 September, ranged from 1.5 to 3.5 inches within 50 miles of Florence's track. The greatest amounts were concentrated in the extreme southeast portion of the state near the landfall area at the Jean Lafitte National Wildlife Refuge which received a 24-hour total of 3.25 inches. Another area of large rainfall totals were centered northwest of Baton Rouge, where most stations reported totals near 2.5 inches for the 24-hour period. It was in this area that the largest 24-hour rainfall total, 4.05 inches, was reported by a cooperative observer at Watson, Louisiana.

In general rainfall along the Mississippi and Alabama Gulf coasts was less than 3 inches.

3. Tornadoes

There were no reports of tornadoes over southeastern Louisiana where Florence made landfall, giving an indication of the weak convective activity associated with the center of the storm. Nevertheless, nine tornadoes were reported in Walton County and one waterspout was reported in Bay County over the Florida panhandle, far from the center of the hurricane. Satellite imagery showed a significant convective band associated with Florence, moving across the western Florida panhandle at this time.

c. Casualty and Damage Statistics

There were no deaths or injuries attribute to Hurricane Florence in Louisiana, however, one man died in Alabama while attempting to secure a boat in Mobile Bay. An estimated 20,000 people were evacuated from the coastal Parishes of Louisiana, including nearly all 2000 Grand Isle residents. Minor storm surge flooding ocurred mostly outside the levee system of Plaquemines, St. Bernard, and St. Tammany Parishes. Grand Isle suffered extensive beach erosion, losing approximately 40 feet of beach. Ligh to moderate wind damage was mostly confined to trees throughout the parishes of Orleans, Jefferson, Plaquemines, St. Tammany, and St. Bernard, causing extensive electrical power outages. It is estimates that 150,000 people were without power for some period of time during the storm. Total damage from Hurricane Florence in southeast Louisiana is estimated to range between $2 Million and $2.5 Million.

Besides Louisiana, the states of Mississippi and Alabama were affected slightly by Florence. Minor evacuations occurred in each state for residents living in low-lying or coastal areas, but no reports of damage were received. The panhandle of Florida, however was an exception. The worse flooding in 10 years occurred when rainfall from Florence was adding to the already swollen rivers of Coldwater and Blackwater in Santa Rosa County. Thirty homes were destroyed and fifty more were damaged along their banks with uninsured losses of $320,000. Damage was estimated at $100,000 due to the tornadoes in Walton County and the waterspout in Bay County.