Visible satellite image of Isaac as of 10:15 a.m. EDT (NOAA)

Extent of tropical storm force winds at 11 a.m. EDT shaded in orange. Blue shaded areas indicate tropical storm warnings, red shaded areas indicate hurricane warnings. (National Hurricane Center)

It is extremely important not to focus on the exact location of the center of the storm. Heavy rain, damaging wind, tornadoes, and storm surge will extend far away from the center.

The center has been a bit disorganized, but is now within range of the New Orleans radar for convenient and constant tracking.

Disorganized or not, any tropical cyclone is capable of producing large amounts of rainfall. As we saw in Haiti and Florida, a tropical storm quickly unloaded 6”, 12”, and even 20” of rain. This morning’s updated rainfall forecast for the south-central U.S. is shown below, with a peak of almost 18” over southern Mississippi.

Rainfall forecast over the next five days. (NOAA/HPC)

The surge is in addition to whatever the normal lunar tide is at the time; so if the peak surge occurs during high tide, that’s much worse than if it occurs during low tide.

Coastal areas in MS and AL (Bay St. Louis, Gulfport, Biloxi, Mobile) will generally be near low tide this afternoon/evening, while Lake Ponchartrain at New Orleans will have its highest tide at 5:22pm CDT... rather poor timing.

Here is a video update on Isaac from CBS News:

Tropical storm Isaac is set to make landfall as a hurricane on the seventh anniversary of Hurricane Katrina

Stay tuned to the CWG blog throughout the day for further updates on Isaac and its impacts.

* Brian McNoldy is a senior researcher at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science.