Hurricane Opal

Hurricane Opal Preliminary Report

Excerpts courtesy of the
National Hurricane Center (NHC) --Written by Max Mayfield

Synoptic History        

Satellite imagery and synoptic analyses indicate that Opal originated from a tropical wave that emerged from the west coast of Africa on 11 September. The wave moved westward across the Atlantic into the western Caribbean Sea by 23 September and merged with a broad area of low pressure centered in the vicinity of 15N 80W. The combined system drifted west-northwestward toward the Yucatan peninsula over the following few days without significant development. Deep convection increased near the center of the low and the post-analysis "best track" shows that a tropical depression formed about 70 nmi south-southeast of Cozumel, Mexico at 1800 UTC 27 September.

Steering currents were weak and the tropical depression moved slowly over the Yucatan peninsula for the following three days. Convective banding increased and ship reports suggest that the depression became Tropical Storm Opal at 1200 UTC 30 September while centered near the north-central coast of the Yucatan peninsula. The storm gradually strengthened and moved slowly westward into the Bay of Campeche.

Air Force Reserve unit aircraft investigating Opal over the southwestern Gulf of Mexico reported that the minimum central pressure steadily dropped. Aircraft reports and satellite estimates suggest that Opal strengthened into a hurricane near 1200 UTC 2 October while centered about 150 nmi west of Merida, Mexico. A banding type eye appeared in satellite imagery later in the day while a large amplitude mid- to upper-level trough moving into the central United States began turning Opal slowly toward the north.

On 3 and 4 October, the hurricane turned toward the north-northeast and gradually accelerated. During this period, the water temperature beneath the hurricane's circulation was near 28 to 29 deg C., and a large upper-level anticyclone was well established over the Gulf of Mexico. Rapid intensification occurred not only as a result of these favorable environmental conditions on the large scale but, and perhaps mope importantly, due to significant changes on a smaller scale within the hurricane's inner core. Opal intensified into a category four hurricane on the Saffir/Simpson Scale early on 4 October at which time reconnaissance aircraft reported a small, 10 nmi diameter eye. The minimum central pressure of 916 mb, with maximum sustained surface winds estimated at 130 knots, occurred when the hurricane was centered about 250 nmi south-southwest of Pensacola, Florida near 1000 UTC 4 October. The peak intensity appears to have occurred near the end of an eyewall contraction cycle. Soon thereafter, the small inner eyewall diminished as an outer eyewall became more dominant. The hurricane weakened during this process, but was still a marginal Category 3 hurricane as the center made landfall at Pensacola Beach, Florida near 2200 UTC 4 October. The collapse of the inner eyewall, reduced sea surface temperature along the Gulf coast and increased upper-level westerlies likely contributed to the weakening.

The hurricane was moving north-northeastward near 20 knots at landfall with the sustained hurricane force winds in the eastern quadrants of the circulation primarily between Pensacola Beach and Cape San Blas. The minimum central pressure at landfall was 942 mb. Maximum sustained surface winds are currently estimated at 100 knots in a narrow swath at the coast near the extreme eastern tip of Choctawhatchee Bay about midway between Destin and Panama City. Although no official reports of surface winds were received within this area, data from reconnaissance aircraft and Doppler radar suggest that the peak winds occurred in this location. It should be emphasized that the strongest winds were in a very limited area and most of the coastal areas of the Florida panhandle experienced winds of a Category 1 or Category 2 hurricane (between 65 and 96 knots). Although the winds were diminishing at the time of landfall, extensive damage due to storm surge and breaking waves occurred over most of the coastal areas of the Florida panhandle.

Opal weakened rapidly after moving inland, becoming a tropical storm over southern Alabama and a tropical depression over southeastern Tennessee. The cyclone was declared extratropical on the best track as it moved northeastward over the Ohio Valley and eastern Great Lakes into southwestern Quebec. The strongest winds occurred well away from the center of the cyclone during the extratropical stage.

Meteorological Statistics

U. S. Air Force Reserve aircraft provided a total of 38 operational center fixes during approximately 122 flying hours of reconnaissance on this hurricane. The minimum central pressure reported by aircraft was 916 mb at 0945 UTC 4 October. This represented a 53 mb drop in pressure within 24 hours and a 42 mb fall within 12 hours. This was a very rapid rate of deepening, but it is not unprecedented. Several western North Pacific typhoons have deepened at an even faster rate. The maximum winds of 152 knots from a flight-level of 700 mb were measured shortly after the 916 mb pressure report. At 2006 UTC, approximately two hours prior to landfall, the aircraft reported 126 knots 59 nmi east of the center. In addition to the Air Force Reserve reconnaissance, a NOAA aircraft flew a 10 hour research mission at the time of landfall.

A ship with call sign XCKX reported 75 knot winds at 1200 UTC 4 October while located about 90 nmi west-southwest of the hurricane center. Several other ship reports were helpful in defining the extent of tropical storm force winds.

The strongest winds reported by a land station were 73 knots with gusts to 125 knots from Hurlburt Field, Florida.

Isolated tornadoes were reported from the Florida panhandle to the mid-Atlantic states. One fatality occurred in Crestview, Florida as a result of a tornado. Another tornado inured several people and severely damaged a number of structures as it swept through Charles, Prince Georges and Anne Arundel Counties in Maryland.

At the time of this report a post-storm high water mark survey was being conducted by the U. S. Geological Survey. Many high water marks remain to be surveyed and "tied into" bench marks. The locations of the maximum values cannot be finalized until the survey is complete. However, initial survey results show an extensive storm surge from southeastern Mobile Bay and Gulf Shores, Alabama, eastward through the Florida panhandle to Cedar Key, Florida. Still water mark elevations inside of buildings or tide gage maximums, which damp out breaking wave effects and are indicative of the storm surge, ranged from 5 to 14 feet above mean sea level. Outside water marks on buildings or debris lines on sand dunes within 200 feet of the Gulf of Mexico shoreline generally ranged from 10 to 21 feet. For example, the tide gage at Panama City Beach pier recorded a maximum of approximately 8.3 feet above mean sea level, indicative of storm surge. At the end of the pier a debris line elevation of approximately 18 feet above mean sea level was recorded. Thus, the breaking waves on top of the storm surge added approximately 10 feet. Many structures in this combined storm surge and breaking wave zone that were not elevated high enough suffered major structural damage.

The combination of Opal and a frontal system resulted in heavy rains along the path of the hurricane. Rainfall totals generally ranged from 5 to 10 inches over portions of the Florida panhandle, Alabama, and Georgia. Rains in South Carolina averaged 2 to 4 inches while in North Carolina 3 to 5 inches were common. Highlands, North Carolina recorded 8.95 inches and Robinson Creek, North Carolina recorded 9.89 inches. Elsewhere, 1 to 3 inch totals occurred over portions of the northeast U. S. from Maryland northward. These rains have been described as beneficial to areas of the northeast U. S. that had been experiencing a prolonged dry period.


Casualty and Damage Statistics

The total number of deaths directly associated with Opal is currently set at 59, and were distributed as follows:

     Guatemala - 31 (from flooding during the developing stages of Opal).

     Mexico - 19 (from flooding)

     U.S. - 9 including:

       Florida (1 from a tornado)

       Alabama (2 from a tree falling on a mobile home)

       Georgia (5 from falling trees)

       North Carolina (1 from a tree falling on a mobile home)

There were no reported deaths due to storm surge flooding, which is remarkable in view of the vulnerable population and extensive salt water damage observed.

The Property Claim Services Division of the American Insurance Services Group preliminary estimate of insured property damage for the United States is $2.1 billion. Considerable uncertainty exists concerning the amount of additional damage due to flood claims, uninsured property damage (including damage to roads and bridges and other government property) and the cost of cleanup. If the estimate of insured property damage proves to be correct, the total damage estimate from Hurricane Opal could reach $3 billion. Without adjustments for inflation, Opal could rank as high as third on the list of costliest twentieth-century U. S. hurricanes. With adjustments for inflation, Opal will likely still be ranked in the top ten on that list.

Most of the severe structural damage occurred at the coastline. The crumbled piers, demolished homes, and eroded or submerged highways were primarily a result of storm surge. In addition, however, strong winds spread damage well inland. Opal downed numerous trees, knocking out power to nearly 2 million people in Florida, Alabama, Georgia, and the Carolinas. The Robert Trent Golf Course in Opelika, Alabama lost over 7000 trees during the storm. Many people in Florida were without water for several days.



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