Isaac Downgraded to Tropical Storm; Continues to Produce Life-threatening Hazards from Storm Surge and Inland Flooding, Aug. 29, 2012 – UPDATE 4 pm CDT

Tropical Storm Isaac Surface Wind Field

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Miami, Florida—(ENEWSPF)—August 29, 2012 – UPDATE 4 pm CDT (2100 UTC).  The National Hurrican Center reports that Tropical Storm Isaac is producing life-threatening hazards from storm surge and inland flooding as it moves slowly across southeastern Louisiana.  Isaac is located 30.0 north, 91.1 west, about 35 miles (60 km) south of Baton Rouge, Louisiana with maximum sustained winds of 70 mph (110km/h).  Present movement is northwest or 310 degrees at 6 mph (9 km/h).

Changes in Watches and Warnings with this Advisory

None.

Summary of Watches and Warnings in effect:

A Tropical Storm Warning is in effect for:

  • Cameron, Louisiana to the Alabama-Florida border.

For storm information specific to your area, please monitor products issued by your local National Weather Service Forecast Office.

Discussion and 48-hour Outlook

At 400 pm CDT (2100 UTC), the center of Tropical Storm Isaac was located by NOAA Doppler Weather Radar near latitude 30.0 north, longitude 91.1 west. Isaac is moving toward the northwest near 6 mph (9 km/h). This general motion is expected to continue through tonight, followed by a turn toward the  north-northwest by Thursday night or early Friday. On the forecast track, the center of Isaac will move farther inland over Louisiana tonight and tomorrow, and move over southern Arkansas by early Friday.

Maximum sustained winds are near 70 mph (110 km/h), with higher gusts. Steady weakening is forecast during the next 48 hours as Isaac continues to move farther inland, and Isaac could become a tropical depression by Thursday night.

Tropical-storm-force winds extend outward up to 175 miles (280 km) from the center. During the past hour, a wind gust to 70 mph was reported at Marsh Island, Louisiana, and a gust to 67 mph was reported at Gulfport, Mississippi.  Also, tropical-storm-force winds have been occurring continuously at Shell Beach, Louisiana for more than 24 hours.

The estimated minimum central pressure based on nearby surface observations is 975 mb (28.79 inches).

Hazards Affecting Land

Even though Isaac is no longer a hurricane, life-threatening hazards from storm surge and inland flooding are still occurring.

Storm Surge. The combination of a storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters. The water could reach the following depths above ground if the peak surge occurs at the time of high tide:

  • Mississippi and southeastern Louisiana…6 to 12 ft.,  
  • South-central Louisiana…3 to 6 ft.,  
  • Alabama…2 to 4 ft., and  
  • Florida Panhandle and Apalachee Bay…1 to 2 ft.

The deepest water will occur along the immediate coast in areas of onshore winds.  Surge-related flooding depends on the relative timing of the surge and the tidal cycle, and can vary greatly over short distances.  For information specific to your area, please see products issued by your local Weather Service Office.  Near the coast, the surge will be accompanied by large and dangerous waves. Storm surge values near 7 feet have recently been reported at Waveland, Mississippi.

Wind. Tropical Storm conditions will continue across the warning area through tonight. Winds affecting the upper floors of high-rise buildings will be significantly stronger than those near ground level. At about the 30th story, winds would likely be one Saffir-Simpson category stronger than at the surface.

Rainfall. Isaac is expected to produce total rainfall amounts of 7 to 14 inches, with possible isolated maximum amounts of 25 inches, over much of Louisiana, southern and central Mississippi, southwest Alabama and southern and central Arkansas through Friday. These rains could result in significant lowland flooding. An unofficial rainfall total of 22.5 inches has been reported in Arabi, Louisiana, which is near the ninth ward district of New Orleans. An official report of 17 inches of rainfall has been received from Audubon Park in New Orleans.

Tornadoes. Isolated tornadoes are possible along the central gulf coast region and parts of the lower Mississippi river valley through Thursday.

Surf. Dangerous surf and rip current conditions will continue to affect the west coast of Florida and the northern gulf coast for the next day or so.

Source: nhc.noaa.gov