Isaac remains a tropical storm as we hit the evening hours but is improving in its organization across the southeastern portions of the Gulf of Mexico. Isaac is moving on a steady west-northwest clip and will work towards a landfall somewhere along the central Gulf of Mexico on Tuesday night into Wednesday.
A relatively marked shift in the models, save for the Euro, has taken place. Most modeling suggests a landfall to New Orleans' west, with the Euro and UK both holding consistently to a landfall east of New Orleans, with the Euro suggesting a Mobile/Pensacola landfall point. The indecision in modeling, even less than 48 hours out, is due to the handling of a trough that is digging through the eastern US (a cold front that will cross us on Tuesday morning) and how a developing disturbance in the mid atmosphere over the Rockies today pushes east. The Euro suggests an ever-so-slightly sharper trough in the East, which pulls Isaac into Alabama according to its projections. The GFS is weaker with this trough and the result is that the storm misses the trough and is nudged back west along the Gulf Coast as the storm is trapped under a ridge in the atmosphere.
Despite these differences resulting in a 250 mile spread in model guidance, Isaac is a large enough storm will impacts will be felt over a relatively large geographic area regardless of how strong it gets. We won't project any doom and gloom scenarios -- there are enough of those already floating around out there -- but the potential for a strong hurricane (perhaps a major) at landfall do exist. Wind shear is modest and oceanic temperatures are warm. The Gulf is not as heated as in 2005 so we should not see a Cat 5 type bombing like we did with storms a few years ago. Also, Isaac's a larger storm system with a pretty large center of circulation. It has taken it a while to organize as it has emerged away from Cuba, dealing with some land interaction with Cuba but also with some wind shear. As both of those influences wane, the storm should intensify tonight into tomorrow into a hurricane.