Tropical Storm Isaac -- yes, it's still a tropical storm -- remains rooted on a northwestward path that will take it on an agonizingly slow journey across the New Orleans area on Tuesday and Wednesday as a Category 1 hurricane, according to the 10 p.m. forecast of the National Hurricane Center. The center of Isaac will make landfall near the mouth of the Mississippi River at about 7 p.m. Tuesday, be over New Orleans at 7 a.m. Wednesday, and won't reach the north shore of Lake Pontchartain until 7 p.m. Wednesday.
The 10 p.m. forecast path of Tropical Storm Isaac.Isaac's top winds of 90 mph is a downgrade from the center's 4 p.m. forecast and reflects the storm's continuing inability to get its act together. Dry air seems to have been dragged into its central circulation just as infrared and microwave imagery indicated a strong band of convection, perhaps the beginning of an eyewall, was wrapping around the south and east sides of Isaac's thunderstorms, according to a forecast discussion message written by Senior Hurricane Specialist Dan Brown and Hurricane Specialist Eric Blake.
Blake is a native of Metairie, by the way.
The result of the disrupton was observed by aircraft flying through the storm this evening, which found the band of heavy thunderstorms -- convection to meteorologists -- was open on Isaac's northwest side, and the low-level center of circulation, where the storm's lowest pressure is located, was south of the rotating clouds seen in satellite pictures.
"The minimum pressure has not fallen significantly during the past several hours and the NOAA and Air Force aircraft have not reported winds any higher than what was measured late this afternoon," they wrote.
Isaac was having a difficult time gaining strength Monday evening.Still, the duo warn that conditions remain ripe for Isaac to strengthen until a forecast 7 p.m. landfall on the west side of the mouth of the Mississippi River.
At 10 p.m., Isaac was about 190 miles southeast of the river's mouth and 255 miles south southeast of Biloxi, with maximum sustained winds of 70 mph, as it moved northwest at 10 mph.
A hurricane warning remains in effect for the coastal area east of Morgan City to the Alabama-Florida border. That includes the New Orleans metropolitan area, and Lakes Pontchartrain and Maurepas. The Baton Rouge area remains under a tropical storm warning.
A flash flood watch is in effect for all of southeast Louisiana and south Mississippi from 7 a.m. Tuesday through Wednesday evening, with rainfall totals of between 10 and 15 inches over a 36-hour period, with up to 20 inches possible in some locations.
Rainfall rates may overwhelm drainage systems and pumps, resulting in rapid runoff and street flooding, forecasters warned.
Isaac's first outer bands of rain were moving over the New Orleans area Monday evening.Hurricane force winds are forecast to last for many hours with this storm, according to the Slidell office of the National Weather Service, with maximum winds in southeast Louisiana predicted to be generally between 55 and 75 mph, with gusts to 90 mph.
The combination of storm surge and astronomical tides of up to 10 feet above mean sea level near the coast could result in flood inundation of 6 to 9 feet above ground level in areas outside hurricane levees. Locations most at risk of surge flooding including low-lying areas bordering Lakes Pontchartrain and Maurepas and in the area near the Chef Menteur and Rigolets passes. Surge flooding should begin early Tuesday morning, increasing on Tuesday night and Wednesday.
Isolated tornados also are possible as Isaac approaches the coast and moves inland.
