Isaac Q and A

| August 26, 2012 @ 4:48 pm

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I have produced a Sunday evening Weather Xtreme special… take a little time to watch it for the meteorological details of Isaac, and scroll down for Bill Murray’s posts.

This will simply serve to answer some commonly asked questions about Isaac and the ultimate impact on the Gulf Coast states.

WHERE AND WHEN WILL ISAAC MAKE LANDFALL? Still can’t answer that with great confidence. The models have clearly shifted west today, favoring a landfall somewhere over Southeast Louisiana or Mississippi. But, we still have the RPM and ECMWF showing a Florida Panhandle landfall.

Let’s ride with the late afternoon NHC track… with a landfall near the mouth of the Pearl River and Lake Borgne. Then, a slow northward motion up I-55 toward Jackson and Memphis as it weakens. But, there is a decent chance this will be adjusted again.

NHC now has landfall coming Wednesday morning.

HOW STRONG? Quite frankly, this question is harder than the track question. Clearly there is something within the inner structure of Isaac limiting strengthening so far. The system is still at only 60 mph, and there has been minimal impact on the Florida Keys. And, despite the tornado watch, I am not aware of a single tornado, or even a torando warning over South Florida today. This is all good.

Conditions seem favorable for Isaac to become a major hurricane (Category 3) at the time of landfall, but almost all tropical models keep the hurricane as a category one or two. It does look like dry has entered the circulation from the south, wrapping around the east side this afternoon. That might be a limiting factor.

NHC has Isaac as a category two at the time of landfall, which I think is the best solution for now.

COASTAL IMPACT: NHC has issued a hurricane warning from Morgan City, LA to Destin, which of course, includes all of the Alabama and Mississippi coast. Remember, most of the storm surge damage and real issues will be along and about 50 miles east of the landfall center. The current NHC track would mean potential for storm surge damage on the Mississippi and Alabama coast, and voluntary evacuations are underway now in places like Gulf Shores.

People on the AL/MS Gulf Coast need to prepare now for a 6 to 12 foot storm surge, based on the latest NHC advisory. In addition, extended power outages are likely as well over Mobile and Baldwin Counties beginning late Tuesday night. Be sure and follow the instructions of local governments.

INLAND IMPACT: It all depends on the track and the intensity. But, let’s ride with the latest NHC package.

First off, it still doesn’t make much sense to ask about specific counties or cities. Tropical systems are large, and can produce similar conditions across a wide area.

Rain amounts of 5 to 10 inches will be possible over North and Central Alabama Wednesday and Thursday, with potential for not only flash flooding, but also river flooding. In addition, we will be a favorable position for a few small tornadoes in the spiral bands around the circulation. These are not like the strong/violent tornadoes we see in spring, but still they are capable of producing significant damage, and warnings are issued for them.

Sustained winds will be in the 20-40 mph range… with this kind of wind we will not recommend leaving mobile homes, but should Isaac come into the coast stronger than forecast, that might change.

WHAT ABOUT POWER OUTAGES FOR NORTH/CENTRAL ALABAMA? If Isaac makes landfall as a category two, we might see scattered outages here, but nothing widespread like Ivan, Katrina, or Frederic. But, should Isaac become a major hurricane, then extensive tree damage with major outages are possible, that could last for days. Let’s hope the NHC forecast is correct. You still might be sure you have plenty of batteries and good ways of charging your phone and various electronic doo-dads.

WILL SCHOOLS BE CLOSED? I have no idea. If there is a serious flooding threat, school officials might consider that for parts of the region Wednesday and Thursday, but that is way too early to even talk about.

SHUTTLESWORTH/BIRMINGHAM AIRPORT: Expect flight delays Wednesday and Wednesday night, and maybe even into Thursday. A ground stop is possible along the way, but I do think the flights will get out. Just maybe not on time. Be ready to be very patient. Conditions will improve by Friday.

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Keep an eye on the blog for running updates through the week as Isaac gets closer, and the answers become more clear…. the next Weather Xtreme video will be posted here by 7:00 a.m. tomorrow….


Category: Alabama's Weather

About the Author ()

James Spann is one of the most recognized and trusted television meteorologists in the industry. He holds the AMS CCM designation and television seals from the AMS and NWA. He is a past winner of the Broadcast Meteorologist of the Year from both professional organizations.

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