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.