Communities from Lake Charles, La., to Mobile, Ala., are feeling the effects of Isaac with conditions deteriorating into Tuesday night.
Isaac showed signs of strengthening Tuesday morning with an eye forming and flight-level winds from aircraft increasing.
Isaac finally became a hurricane Tuesday midday after traveling thousands of miles since emerging off the coast of Africa.
Landfall along the southern coast of Louisiana is forecast by AccuWeather.com Tuesday night, considering that the center may brush the coast for a time while moving west-northwest.
A larger version of the latest forecast track map for Isaac (with times in EDT) can be found on the AccuWeather Hurricane Center.
Ironically, Isaac is expected to threaten lives and property along the northern Gulf Coast almost seven years to the date of Hurricane Katrina's devastating landfall.
As the AccuWeather.com Hurricane Center has been calling for since last Thursday, Isaac is expected to slam into the northern Gulf Coast Tuesday afternoon or evening as strong as a category 1 hurricane (with maximum sustained winds between 96 and 110 mph).
A developing split between high pressure over the interior United States is directing Isaac toward the Louisiana Coast Tuesday and Tuesday night.
Isaac will pound those in its path with destructive winds, widespread flooding rain and perhaps isolated tornadoes.
A track into southeastern Louisiana would spell trouble for New Orleans, Biloxi and Mobile in terms of storm surge.
Such a track will still cause water from Lake Pontchartrain to put stress on the city's levee system.
Winds circulating around Isaac would still funnel some water from the Gulf of Mexico directly into Mobile, via Mobile Bay.
With Isaac's path will drive significant storm surge around Houma and Morgan City, La. Tuesday night.
Those at risk of taking a direct hit by Isaac should closely monitor the progress of the storm, heed all evacuation orders and avoid flood-prone areas.
The dangers of Isaac will not end when the storm makes its final landfall. Flooding rain and the potential for isolated tornadoes will accompany Isaac inland through the South.
Dry and sunny conditions will continue in San Francisco for the the official start to winter and the Christmas holiday.
Sunshine will return in full force for the weekend, the official start to winter, and Christmas in Los Angeles.
Big changes are on the way for parts of the Western and Central states late this week and into this weekend.
Similar to the days prior to Thanksgiving, the worst weather will focus on the days prior to Christmas as millions of travelers take to the roads and skies in the U.S. and southern Canada.
Warm air is forecast to surge into much of the eastern half of the nation by the weekend and will be accompanied by heavy rain and flooding risk in some locations.
Thunderstorms in parts of the South this weekend may become strong enough to threaten lives and property.
Philadelphia, PA (1948)
7.4" of snow - Eagles beat Chicago Cardinals 7-0 for NFL title.
West Palm Beach, FL (1989)
Record high of 88 degrees.
Lancaster, CA (1984)
Ended up with about a foot of snow. One spot in Kern County (North of LA) had 19" of snow.