8/27 - 9:30pm - Update on Isaac's Expected Gulf Coast Landfall

Tropical Storm Isaac is teetering on the edge of becoming a hurricane this evening with winds of 70 mph as of this writing. The threshold for a Category 1 hurricane is 74 mph. The storm motion has slowed down over the past few hours, now moving northwest at only 10 mph. Issac continues to run into issues that prevent it from rapid intensification, which is certainly good news. The latest issue is a batch of dry air that is currently being pulled into the center of the storm. Without an uninhibited source of moist air the storm cannot form a defined eye or intensify very well. The dry air is why Isaac is lopsided right now with most of the intense winds on the south side.

How long will it be until this dry air is finished working through the storm? Probably a few more hours, possibly lasting into the early morning hours tomorrow if current model forecasts are correct. Speaking of models, the current track from the National Hurricane Center takes Isaac right into the Eastern Louisiana/Mississippi Coast areas late tomorrow night into early Wednesday morning as a weak Category 2 storm with 100 mph winds. With the lack of organization we're seeing right now it may only be a Category 1 at landfall. The latest computer model tracks, the spaghetti plots as you've probably heard about and seen over the past few days, have tightened up on a landfall location somewhere around New Orleans. It's worth noting that some of these models are now trending eastward after a massive amount of successive westward jogs in recent days. It doesn't appear that this landfall will take place further east than Biloxi, Mississippi given the current motion of the storm and model data, but the exact landfall location won't be the big story with this storm.

Storm surge exceedance probabilities

The big story here is how big and how slow this storm is. Sure, there will be some wind damage along the coast as the storm makes landfall, but the large area that Isaac covers means that quite an expansive area along the Gulf Coast will experience other effects from it. Storm surge at or above ten feet is possible in locations from New Orleans to Pascagoula, MS and rainfall amounts over a foot are forecast over much of Central and Southern Mississippi and Eastern Louisiana. Isaac will slow down even more than its current speed once it gets over land so heavy rain will be a good bet across much of the Gulf Coast states until we get into the weekend. Inland flooding will be a problem with the deluge that Isaac with unleash on the region as it crawls northward.

Rainfall through 7pm CDT Saturday

As far as local effects in North Mississippi and West Tennessee, Isaac will bring very heavy rain and winds with gusts in some cases near 40 mph. Starkville, MS may be looking at a six or more inch rainfall scenario through Saturday evening and areas in West Tennessee like Jackson will likely see more than three inches of rain. This highly depends on Isaac's exact track so some areas will see much more rain than others.

With just about any landfalling hurricane you can expect the threat of isolated tornadoes, and Isaac will be no different. The turning of winds with height in a hurricane or tropical storm create favorable wind shear for tornadoes to form in stronger parts of it. Due to this potential threat, the Storm Prediction Center has issued a Slight Risk for most of Mississippi and parts of Louisiana, Alabama, Georgia, and Florida.


So overall we're not looking at Isaac to be a major hurricane at landfall, but the effects from it will be widespread due to it's large size. It's a good thing that folks in a wide area are preparing for this storm since it could be a long haul given the slow motion that's expected from it.

8/23 - 5pm - Tropics, Drought, Storms... Anything Else?

Computer model forecast tracks for Isaac

The big shakeup in the world of weather right now is the presence of Tropical Storm Isaac south of Puerto Rico. Much uncertainty still exists with where the storm will go but certainty of it making some sort of US landfall is growing. Current forecast data from multiple computer models has this storm going anywhere from the eastern Florida Peninsula to the Central Gulf over the coming days. The trend has been for these forecast tracks to shift westward over the past couple days and that means that those with interests along the Gulf Coast need to watch this storm extremely carefully. The fact that this storm may miss most of Hispanola and it's rough terrain means that we could have a stronger storm than previously expected by the time it reaches the Gulf. Once we get some better data tonight from a NOAA Gulfstream IV aircraft that is being dispatched to take measurements of the storm the model data and forecasts should improve a bit.

The 5pm EDT National Hurricane Center update on Isaac has again taken a more westerly track than before thanks to the latest model data. Their forecast has Isaac remaining a tropical storm until it clears the north side of Cuba on Monday and becomes a hurricane. This all depends on where the storm tracks because the less of Cuba and Hispanola it goes over, the more time over warm water it will have. Should the storm remain weak like it is now for a longer period, a more westerly track can be expected.

How 'bout the drought? Not much has changed from last week's drought monitor product for West Tennessee and North Mississippi. Much of West Tennessee is still suffering from a severe to exceptional drought, especially in areas near the Mississippi River and Kentucky border. The area of exceptional drought, the highest level possible, has contracted a bit since last week. Areas south of Benton County and east of Bolivar aren't faring as badly as the rest of West Tennessee, but it's worth noting that rain may be hard to come by over the next week. The worst of North Mississippi's drought is still confined to areas near Tunica and areas south of West Point don't have drought conditions at this time.

Speaking of rain, we're looking at just a small chance for some isolated showers and storms on Saturday afternoon in North Mississippi as an upper-level system moves toward us from the west. This will increase our moisture and instability a touch since winds will be turning more southerly at the surface. West Tennessee will be too far north for this storm chance unfortunately. Small storm chances will be in the forecast again as we head into the early part of the workweek, but uncertainly skyrockets after that because our weather will depend on where Isaac, by then likely a hurricane, will go. A more westerly landfall along the Gulf Coast would mean quite a bit of rain for the region while a more easterly landfall in Florida wouldn't affect us too much. This again is something we'll need to watch.