Thursday 8/30 Update

Good Thursday!  One more dry and fairly hot day ahead, then we'll be dealing with Isaac.  The front edge of Isaac's cloud cover is moving into the area from the south this morning.  Local 6 viewer Gary Hargrove shared a dramatic shot of those clouds arriving against the backdrop of some morning sunshine:

Since yesterday, we haven't seen much change to the forecast track of the remnants of Isaac over the next few days...still looks like it heads through Arkansas and into central MO, then takes a sharp turn to the east and crosses central IL & IN:

One last time with this system, here's a rundown of what the models are showing.  Remember, the colored portion of these charts represent 6-hr precip accumulation.

GFS at 7PM Friday:

7AM Saturday:

7PM Saturday:

7AM Sunday:

7PM Sunday:

Now the European model...starting at 7PM Friday:

7AM Saturday:

7PM Saturday:

7AM Sunday:

7PM Sunday:

Feel pretty confident that the most widespread showers and storms will remain to our southwest through Friday morning.  That is when our chances will start to increase.  Lots of moisture will be surging in, allowing for widely scattered showers and storms to increase across our area for Friday afternoon and evening.  Not looking for continuous rain Friday night, but certainly periods of storms, some with heavy rain, and some gusty winds up to 30 mph....possible higher if an isolated severe storm or two can develop. With any tropical system, there is a decent amount of wind shear, so while the threat of severe weather is low, there is a chance of isolated severe weather where some pockets of heating and instability develop....and an isolated weak tornado can't be ruled out.  Saturday will likely be the wettest day of the weekend, with Sunday seeing chances diminish slightly as the system continues to weaken and move away.

Rainfall totals continue to be highly dependent upon the exact track of the center of the low and where some training of showers and thunderstorms occur.  Here's a couple of looks at different forecast models and agencies' forecasts.

Latest HPC forecast (KY: 1.5"-3.0"....IL: 2.5"-4"....MO: 1.5"-4"...TN: 1-2"):

Latest GFS forecast (KY: 1-2"...IL: 2-2.5"...MO: 1.5-2.5"...TN: 0.5-1.5"):

Of the two above, the HPC trend is worth noting, but I believe it may be a bit too much.  Meanwhile, the GFS looks more reasonable.  I think a good middle of the road is the European model that I showed this morning on Local 6 Today:

Will be interesting to see how this all plays out.  It's sure been a challenging forecast!
Finally, we need to look ahead to next week, including the Labor Day holiday.  After we say goodbye to Isaac, there will be a lot of tropical moisture left behind.  As skies clear, this means very warm and humid conditions for the first half of the week.  There is a chance of scattered storms on Monday, especially during the afternoon hours...but certainly not a washout.  Outdoor plans for Monday are okay for now, but keep an eye out for those scattered storms. 

Wednesday 8/29 Update

Good afternoon everyone!  Time for the latest Isaac update.  The storm is back down to tropical storm status, and will continue to slowly weaken as it crawls inland across Louisiana.  With landfall behind us, it's time to start focusing in on how and when the leftovers of Isaac will affect our weather.  Forecast models seem to be starting to come into good agreement on a track of the system, but they are still all over the place on totals.  This continues to be a very challenging and uncertain forecast.  The NHC track seems to line up well with most forecast models:

Based on the models shown below, it looks like rain chances could arrive in the MO Bootheel/TN as early as Thursday night, with best chances of showers and thunderstorms Friday & Saturday, then tapering off Sunday.

GFS at 7PM Friday:

European at 7PM Friday:

GFS at 7AM Sunday:

European at 7AM Saturday:

GFS at 7PM Saturday:

European at 7PM Saturday:

GFS at 7AM Sunday:

European at 7AM Sunday:

Pretty decent agreement there.  Rainfall totals are still quite uncertain.  Here is the GFS rainfall for this system, keeping most of the area in the 1.0"-1.5" range:

The NAM doesn't go out as far (stops at 7PM Saturday), but limits rainfall over 1" to the western half of the area :

And now here's where it gets really fun....here's what the HPC (NOAA) was forecasting this morning:

Now, this afternoon, they have revised their forecast WAY higher:

Can you start to see why this storm is giving us headaches?  All of these variations in the forecast ultimately center around what happens with a dome of high pressure over the eastern half of the country.  A stronger high means Isaac stays west and we get less rain.  A weaker high curves Isaac closer to our area, and we get more rain.  Bottom line, periods of rainfall is likely for most of the region during the Friday-Sunday time frame.  When it does rain, it will be a tropical rain with heavy downpours.  How much we'll get depends on the exact track of the low, and slight variations could mean big variations to the weather we see from one location to the next.  Winds could also gust as high as 30 mph at times as well.  And there will be a small chance of severe thunderstorms within this system too.  Should be very interesting to see how this plays out over the next few days. 

Tuesday 8/28 Update

Good afternoon everyone!  It's Isaac update time again.  With yesterday's weak cold front on to our southeast, what happens with Isaac is now the primary focus for our forecast heading through the rest of the week.  Isaac was upgraded to a hurricane just before noon today and looks healthier now than ever.

As of the latest update from the National Hurricane Center, hurricane force winds (74 mph or higher) extend out 60 miles from the center of the storm, with tropical storm force winds (39-73 mph) extending out 185 miles from the center.  Here's the latest track from NHC:   

The hurricane warning runs from Morgan City, LA, to the MS/AL border.  Storm surge could reach 6-12 feet in this area...rainfall totals of 7-14 inches are expected, with localized totals as high as 20 inches...hurricane & tropical storm force winds will last for a long duration (some locations near the center could deal with winds for 24-36 hours)...and isolated tornadoes could occur with storms north and east of the center.

Locally, I wouldn't be surprised if we see a couple of isolated showers from the outermost rain bands as early as Thursday.

Looking ahead, the most challenging part of the forecast for Isaac is what will happen as the storm moves inland, and thus, what impacts it will have locally.  It seems like forecast models are starting to line up on a solution...and unfortunately, if current trends continue, we may be missing out on the heaviest rains.  Above, you can see the official NHC track takes the remnants of Isaac over north central Arkansas by Friday afternoon, near St. Louis by Saturday afternoon, and near Chicago by Sunday afternoon.  However, nearly all of the forecast models are in agreement on a track much farther to the west:

Here's what some of the individual models are showing:

The 12Z run of the European model shows the center over western MO at 7AM Saturday, bringing some rain to SEMO & S. IL, but little to KY & TN. 

The 12Z run of the GFS above shows a very similar picture at 7AM Saturday.

By Sunday morning at 7AM, the two models are a little farther apart:

 European model shows the center around the MO/IL/IA border.

GFS at 7AM Sunday is a little farther to the northeast.

The fact that these models are trending farther to the west and north are making it very tough to get excited about our rain chances....and tough to nail down a forecast.  Based on these trends, it looks like SEMO & S. IL have the best chances of noteworthy rainfall, while we're gonna need an eastward shift in things to bring the heavier rains to KY & TN.  Here's a couple of rainfall estimates I've seen today:

This estimate is from NOAA, and is highly dependent upon the NHC track.  Personally, I think it's too far east based on what most models are showing us.  Here's the GFS estimate, which lines up better with other models:

With the uncertainty, I think it's still too early to give any specific rainfall estimates.  I know there have been some numbers floating around today, but I think we need to see another day's worth of model run agreement to start getting real specific.  Still think the Friday-Saturday time frame is best as far as timing...with rain clearing from west to east by Sunday.  I'll hopefully start talking about totals tomorrow.

Monday 8/27 Update

Good Monday!  A weak cold front/trough is crossing the region this afternoon, sparking numerous showers and thunderstorms. 

 
Highest concentration of showers and storms will be along and southeast of the Ohio River through early evening, when this activity should begin to taper off.  By tomorrow morning, with a cold front off to our east, we'll notice a modest drop in humidity levels, but temperatures will still be running in the lower 90's tomorrow and Wednesday.

The forecast for the end of the week and weekend is highly dependent upon what Isaac ends up doing.  There is still quite a bit of uncertainty in the forecast models, so at this point in time we still can't commit to fully biting on the rain chances being dangled in front of us.  Here's what some of the models are showing us:

Above is the 12Z run of the European model showing conditions at 7AM Saturday.  Notice the black ring labeled "1012" over SEMO and NE AR....that is the center of the remnant low leftover from Isaac, with the shades of green and yellow showing precipitation in our area Friday & Saturday.

Meanwhile, above is the 12Z run of the GFS model, showing conditions at 1AM Saturday.  Same story here, with the remnant low centered very close to St. Louis, and a pretty good swath of rain over our region.  This certainly looks promising....but take this with a grain of salt.  Other runs of the GFS are indicating the leftovers of Isaac could stay farther west:

Something else we have to consider with Isaac is a strong upper level ridge that will be in place over the middle of the nation:

There is a chance that if that ridge holds strong enough, it could keep Isaac over the southern states for a longer period of time, and could prevent it from making progress northward and into our area.  Again, nothing certain with that...we'll have to see how models handle this over the next couple of days.  I think we'll have a better handle on things tomorrow as Isaac gets closer to landfall. Bottom line...while we're growing more optimistic about getting some rain from Isaac, we are keeping rain chances at 40% for Friday & Saturday.  This is a very challenging forecast, and we'll be working hard to keep it updated over the next few days.  The latest HPC forecast seems to be buying in:

As I type, the 5PM EDT advisory from the National Hurricane Center just came out, and Isaac has still not strengthened to a hurricane.  The storm continues to struggle with some drier air being wrapped into the southeast segment of the storm, limiting its ability to undergo more rapid intensification.  Such has been the story with this storm for a few days now.  Here is the latest forecast track from NHC:

No changes to the track today, as it still looks like landfall will occur very close to New Orleans or the Biloxi/Gulfport area.  The forward speed of Isaac is slowing down, which would put landfall sometime during the wee hours of Wednesday morning.  This slowing trend also means a longer period of torrential rain, wind, and storm surge for the areas affected.

Isaac is a very large storm, with tropical storm force winds extending out 205 miles from the center.  Storm surge estimates continue to run 6-12 feet for southeast LA & MS, and 6-9 feet for AL.  Rainfall totals of 6-12 inches are possible, with localized totals as high as 15-20 inches.  A hurricane warning continues for areas near Morgan City, LA, eastward to the AL/FL border.  Areas such as Pensacola and Destin were dropped from the hurricane warning, but are still under a tropical storm warning. 

Sunday 8/26 Update

Good Sunday, hope you have enjoyed this weekend.  Lots to get to tonight, with Isaac of course being the major story today.  Before we get to that, a few words on our weather at home for the first half of the week.

When we wake up on our Monday morning, a cold front will be knocking on our door to the west, leading to a chance of scattered showers & thunderstorms through the day.  Here's the surface map at 7AM Monday:

I believe the highest chances will be across the KY & TN during the PM hours when the atmosphere is at it's juiciest....but once again, things will be widely scattered, and rainfall totals will not be too impressive.  HPC indicating perhaps up to 0.25":

That cold front will be east of the area by Tuesday, leading to the return of sunshine for mid week.  Temperatures will remain pretty hot, with highs in the lower 90's.  Dry weather will stick around through Thursday....which brings us to Friday, and potential impacts from Isaac.  Before we talk locally about Isaac, let's go in depth on the latest with this storm.

Here is the latest advisory from the National Hurricane Center as of 8PM EDT tonight:

Isaac continues to be a strong tropical storm with maximum sustained winds of 65 mph.  It has not been able to make the jump to a hurricane yet because of its close proximity to land (Hispaniola, Cuba, & South Florida), and because of dry air being drawn into the storm.  However, since the 5PM EDT update, winds have increased, and the pressure has dropped, showing us that the storm is getting stronger.  And as the track above indicates, the storm will be spending the next two days over the open waters of the Gulf of Mexico, where sea surface temperatures will work to strengthen the storm.  Wind shear is low as well, another factor favorable for strengthening.  Most likely we'll see this become a hurricane later on Monday evening or Tuesday morning.  Intensity forecasting is one of the most challenging aspects of tropical weather, so this forecast very well could change.

The biggest development with Isaac over the past couple of days has been the westward shift in the projected storm track.  As if forecasting intensity wasn't difficult enough, forecast models have been making the path of Isaac a real headache.  Check out these two models:

Here's the 12Z GFS model, showing landfall in LA:

Meanwhile, the 12Z European model has landfall some 300 miles east on the FL panhandle:

That is a very large difference (about 300 miles), considering this storm is only about 48-60 hours from impact.  But, just after looking at those two models, I ran across another group of model data that seems to be indicating that the more westward solution may be the one to look toward, and data that makes me think the NHC forecast cone will continue to trend westward toward Louisiana:

While this is not a definite by any means, this trend is very concerning for folks around New Orleans.  With this storm approaching from the southeast, the onshore flow (toward the coast) will be strongest on the northern and eastern sides of the eye....this means that a storm making landfall south and/or west of N.O. would funnel storm surge directly toward the city and Lake Pontchartrain.  Not good at all.  Something else to think about...a more westward track means more time over warm waters, which means more time for potential strengthening.  It also means taking this storm toward our highest concentration of oil refineries, so get ready to feel it at the gas pumps.  And while I'm not one for coincidences, it is downright eerie that this storms looks like it will make landfall exactly 7 years to the day after Katrina. 

With all of the that info in mind, the NHC has posted hurricane and tropical storm warnings along the Gulf coast:

The hurricane warning stretches from near Morgan City, LA, eastward to Destin, FL.  This means that hurricane force winds of at least 74 mph are expected in these areas with the next 24 hours.  They also estimate that IF peak storm surge arrives at the same time as high tide, water levels could rise some 6-12 feet within the hurricane warning area.  Total rainfall amounts of 5-10 inches, with localized amounts up to 15 inches will likely accompany the storm.

Now, coming back home, the big question on everyone's mind is how Isaac will affect us locally.  If you check the official NHC 5-day cone, then bring the remnant low/tropical depression to near Memphis by Friday afternoon.  That's a good sign for us!  The GFS & European are also showing some wet weather for us:

European model at 7PM Friday:

GFS model at 1AM Sunday (probably a little too slow):

So, bottom line, what was a big IF last week is looking more likely.  That said, with forecast models still differing a bit, I'm not totally ready to fully commit to putting a soaking tropical rain in our forecast just yet.  But I am getting more optimistic.  One more thing...when many of us hear something about the remnants of a hurricane, it probably stirs up memories of the remnants of Ike in September 2008, when we were pounded with 70-80 mph winds and massive power outages.  I can say with very high confidence that a similar situation is very unlikely with the remnants of Isaac.  Ike was a much more powerful hurricane when it made landfall, which then interacted with a strong jet stream and cold front, creating sort of a "perfect storm" situation.  Those conditions will not be available for this storm.  By the time Isaac reaches us, the winds will be pretty much gone....just leaving behind some rain...we hope!  Stay tuned for additional updates over the next few days!