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 h
eard
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.
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| 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.
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| 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.
Hurricane Sandy is a monster storm. That goes without saying. It's about two hours from landfall as of this writing but that won't matter much due to just how incredibly large the wind field is. Tropical storm winds extend for hundreds of miles from the center of the storm making this the largest hurricane ever recorded in the Atlantic Ocean at over 1,000 miles wide. This is big by area, not by wind speed. While the winds extend for an incredible area the winds in general are at Category 1 speeds near 90 mph. For areas in the tropics this may not sound so bad but for the Northeast this is a disaster since winds rarely get up to that strength with storms up there.
Something that also may be unprecedented here is the extreme snow threat from Sandy for the mountainous regions of West Virginia, Virginia, North Carolina, Tennessee, and Kentucky. Snow totals could be 1 to 2 feet in places when this storm is said and done. The other thing to consider with the size and scope of this storm is the storm surge that continues to roll in. Places like New York City and along the Jersey shore could be dealing with storm surge totals in excess of 11 feet thanks to the pure mass of water that will be coming in with the storm. This will create coastal flooding whereas the high rain totals will contribute to inland flooding. You'll hear about this storm for years to come... 765,000 customers are without power across the Northeast already and this storm is just cranking up.
