Archive for August 26th, 2012
The new forecast package is in from the National Hurricane Center and it is shifted a little further westward again. There has been significant difference in the output of the various dynamical models with Isaac. Hopefully they will come into better agreement today. One camp predicts that Isaac will exploit a weakness in the ridge over the northern Gulf and reach the Alabama or Northwest Florida coast, leading to big impacts across Central Alabama. Another camp, including the GFS, believes that the storm will be steered more westward, south of New Orleans and along the Louisiana coast toward Texas. If that happens, the impact on Central Alabama will certainly be lessened.
Less look at impacts based on the current NHC forecast:
The late night package shifted a little west over the New Orleans area.
Hurricane warnings are in effect from Morgan City to Destin, including all of the Mississippi and Alabama coastlines, and the New Orleans Metro area.
Isaac should become a hurricane Monday morning. A hurricane watch is in effect to east of Panama City. Evacuations will start in Mobile and Baldwin Counties Monday morning, as well as several parishes in southeastern Louisiana.
If this track materializes, here are some of the impacts that can be expected.
Tropical storm force winds will reach coastal Alabama, Mississippi, Northwest Florida and Southeast Louisiana between midnight and dawn tonight. By then, the storm should be slowing its forward motion. Also, the storm will be over some warmer water and should be moving away form the upper low that has been impeding it. We will then be watching for rapid intensification.
Heavy rain and squalls will be moving inland along coastal areas as well. Strong tropical storm force winds will reach southeastern Louisiana tomorrow afternoon, and the area from New Orleans to Biloxi during the evening. Strong tropical storm force winds may stay west of Mobile and Baldwin Counties in this scenario.
Hurricane conditions should arrive at the mouth of the Mississippi River late tomorrow night and reach new Orleans during the morning hours Wednesday. They could last up to 10 hours if the motion slows as expected.
Landfall should be near Buras, Louisiana late Tuesday night, with the eye passing over New Orleans during the morning Wednesday.
Winds should become onshore by early Tuesday afternoon around Apalachicola and that trend will spread westward during the day Tuesday, reaching Destin by evening. When the winds shift, tides will rise rapidly, with storm surge values running around 6 feet over the eastern Florida Panhandle and as high as 12 feet in the funnel between the Mississippi Delta and the Mississippi Gulf Coast, back over to Mobile Bay early Wednesday as winds come onshore there as well.
Tornadoes will also be likely in the northeastern quadrant of the storm over southern Mississippi, Alabama and Northwest Florida.
Rainfall amounts will range up to 10-20 inches across southeastern Louisiana, southern Mississippi, southern Alabama and extreme northwestern Florida.
CENTRAL ALABAMA IMPACTS: If this track materializes, Central Alabama will see showers and storms in feeder bands that will develop Tuesday, continuing at times through Wednesday. Alabama will be in a favorable position to see a few tornadoes. Winds will be gusty at times, but they won’t be damaging. Rainfall amounts should range between 1-2 inches, higher over the west. Things should begin to improve on Thursday as Issac moves up into the drought ravaged areas of Arkansas and Missouri.
STAY TUNED: There is still great uncertainty in this forecast, so please stay apprised of the latest forecast developments until Isaac makes landfall. Remember, that the center of the storm could end up anywhere in the cone of uncertainty, that white shaded area on the graphic. If the track shifts, the impacts will shift as well.
All of Alabama is now under a “state of emergency” as declared by Governor Robert Bentley.
To the south, mandatory evacuations have been called for zones one and two in both Mobile and Baldwin Counties. See the maps below. Scroll down for full details on the Isaac situation.
An all new edition of the ABC 33/40 Weather Xtreme video is available in the player on the right sidebar of the blog. You can subscribe to the Weather Xtreme video on iTunes by clicking here.
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….
Hurricane warnings have been issued from southeastern Louisiana through the Mississippi and Alabama coasts and to Destin on the Northwest Florida coast.
FAST FACTS AT 4 PM
ABOUT 40 MI…65 KM SW OF KEY WEST FLORIDA
MAXIMUM SUSTAINED WINDS…60 MPH…95 KM/H
PRESENT MOVEMENT…WNW OR 295 DEGREES AT 16 MPH…26 KM/H
MINIMUM CENTRAL PRESSURE…992 MB…29.29 INCHES
The forecast track has been nudged slightly to the west. The official skinny black line is over Bay St. Louis MS.
The cone of uncertainty extends from Lafayette LA to Navarre Beach, Florida. The circles of the cone reflect two thirds of the average forecast error at each time period for 12, 23, 36 hours etc.)
The 18z NAM model is in. It reflects a landfall at Mobile Bay on Wednesday afternoon. We haven’t received any GFS 18z output yet.
Air Force reconnaissance just found that the central pressure in Tropical Storm Isaac is down to 992 mb. That represents a drop of 3 mb since the plane last penetrated the center just before 1 p.m.
The early cycle guidance is in for the 18z run and it still heavily leans toward a track toward Southeast Louisiana.