Isaac Landfall Means Increasing Tornado, Flood Threat

Isaac has now been upgraded to a Category 1 Hurricane with max winds of 75mph, still moving NW towards SE Louisiana. Here's the latest satellite image of Isaac showing some robust convection near the center, but also some dry air being entrained right into the center of the storm. Earlier, an eye was trying to form, but the battle with dry air really has won out and prevented Isaac from really strengthening further. This storm is beginning to slow down, so there is still time for intensification, but at this point the main concern will be extensive coastal flooding from 6-12 foot storm surge, as well as inland flooding due to relentless rainfall over the next 36 hours.

Here is the HWRF's depiction of early Wednesday morning at 1 AM, note, the center of the storm is still offshore:

As a secondary concern, with any landfalling tropical system, the threat for spin-off tornadoes exists, especially in the eastern quadrants of the storm in the spiraling bands. We've already had a tornado warning issued for parts of Hancock County and Orleans and St. Tammany Parish earlier today. Here is a current radar picture, showing a gusty squall just south of Hattiesburg moving W:

In terms of the immediate tornado threat, the SPC has issued 2 tornado watches for coastal Mississippi, Louisiana, Alabama, and the western Florida Panhandle, as well as another watch for parts of south Mississippi. Both watches will be allowed to expire at 7 PM, however, additional watches are very likely as Isaac continues to track ashore:

In terms of landfall, it appears Isaac is still on track to come ashore very late tonight and early tomorrow morning near Barataria Bay in SE Louisiana, moving up the bayou towards Lafitte and Port Sulphur. 

With the storm tracking west of New Orleans, we will be seeing strong, persistent onshore flow upstream of all the bayous and bays, and this will pose a great chance of flooding, not to mention the heavy rain. Coastal flooding has already been a problem along the MS coast as well as the FL panhandle. Even though Isaac is not a major hurricane, this system still poses a real threat, especially to low-lying coastal areas. Inland, communities still need to be prepared for extended power outages, really as far north as I-20, downed trees and power lines, and flash flooding in the coming days. 

Here's the latest rainfall estimate from the HPC: