Tropical Cyclone Report - National Hurricane Center - NOAA

would typically suggest an intensity of about 77 kt, however SFMR winds did not increase
further, and several surface measurements made around the time of the highest flight-level wind
continued to support an intensity of 60-65 kt. At 2333 UTC, a Texas Tech University Hurricane
Research Team (TTUHRT) sensor in Buras, Louisiana, measured a peak 1-minute sustained
wind of 65 kt and a gust to 75 kt at an elevation of 2.25 m (7.4 ft). The sensor was located on
top of a levee and was likely affected by wind speed-up effects. Accounting for the possible
speed-up effects and sensor elevation, the TTUHRT estimates that the peak 1-minute sustained
wind at 10 m for that location was 66-67 kt. Isaac’s estimated peak intensity of 70 kt, occurring
between 1800 UTC 28 August and 0600 UTC 29 August, is a blend of the aircraft and surface
data. The highest gust recorded on land was 84 kt by a WeatherBug station in Poydras in St.
Bernard Parish, Louisiana, at 0639 UTC 29 August.
The minimum central pressure of 965 mb around 0300 UTC 29 August is based on a
dropsonde report from the NOAA P-3 of a surface pressure of 966 mb with 12 kt of wind at 0238
UTC. Official stations at Pilot’s Station East at Southwest Pass and Grand Isle reported
minimum pressures of 969.8 mb and 970.0 mb, respectively. Minimum pressures of 967.4 mb
and 967.6 mb were reported by unofficial stations at Montegut and Chauvin, Louisiana,
respectively.
Surface observations of sustained tropical-storm-force winds or greater for the Gulf of
Mexico and surrounding coastal areas are shown in Fig. 7a, while surface observations of
tropical-storm-force or greater wind gusts are shown in Fig. 7b.
Storm Surge 3
Isaac’s large wind field led to extensive storm surge flooding along the northern Gulf of
Mexico coastline, especially in southeastern Louisiana, Mississippi, and Alabama. The highest
storm surge measured by a NOS tide gauge was 11.03 ft above normal tide levels at Shell Beach,
Louisiana, on the southern end of Lake Borgne (Fig. 8). A storm surge of 6.69 ft was measured
at Pilottown, Louisiana, near the mouth of the Mississippi River, and a surge of 6.35 ft was
observed in New Orleans at New Canal Station on the southern shore of Lake Pontchartrain. In
Mississippi, a storm surge of 8.00 ft was measured by the NOS gauge at the Bay Waveland
Yacht Club. Farther east, a storm surge of 4.63 ft was measured in Mobile Bay, Alabama, at the
Coast Guard Sector Mobile facility.
In Louisiana, the following inundation levels, expressed above ground level, were
prevalent near the immediate coast, lakeshore, or levee systems due to the storm tide:
3 Several terms are used to describe water levels due to a storm. Storm surge is defined as the abnormal rise of
water generated by a storm, over and above the predicted astronomical tide, and is expressed in terms of height
above normal tide levels. Because storm surge represents the deviation from normal water levels, it is not
referenced to a vertical datum. Storm tide is defined as the water level due to the combination of storm surge and
the astronomical tide, and is expressed in terms of height above a vertical datum, i.e. the North American Vertical
Datum of 1988 (NAVD88) or Mean Lower Low Water (MLLW). Inundation is the total water level that occurs on
normally dry ground as a result of the storm tide, and is expressed in terms of height above ground level. At the
coast, normally dry land is roughly defined as areas higher than the normal high tide line, or Mean Higher High
Water (MHHW).
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