8/23/12
5:00PM

Max Windspeed: 40mph | Direction: West 16mph |

Since 9AM the forecast for Isaac has been shifting ever so slightly to the west.  This obviously is better news for residents along the western coast of Florida.  However, the current size of Isaac means winds will extend further outward from the center.  Below is a graphic depicting the probability of tropical storm force winds occurring within the next 120 hours (5 days).   As of now southwest Florida is at 40% (Which is considerable this far out).

I am also not seeing any direct impact with Florida’s west coast.  Data over the past 2 days seems to be consistent in a direct impact miss.

Tropical Storm Isaac winds

Below is the current satellite image of Tropical Storm Isaac.  It’s becoming very well define cloud-wise and the feeder bands are becoming extremely well-defined.

Tropical Storm Isaac Satellite Image

As the storm gets closer to Florida, more models are run for accuracy.  The latest run has many more models running and the vast majority are in agreement that Isaac will miss Florida to the west.  However, those models only show the center of the storm.  The size of Isaac will mean that winds will extend into Florida and can still cause widespread damage.

Tropical Storm Isaac Models

Below is the 5PM NHC forecast.

Tropical Storm Isaac Forecast cone

FORECAST POSITIONS AND MAX WINDS

INIT  23/2100Z 16.0N  67.1W   35 KT  40 MPH
 12H  24/0600Z 16.6N  69.0W   40 KT  45 MPH
 24H  24/1800Z 17.5N  71.5W   50 KT  60 MPH
 36H  25/0600Z 18.9N  74.0W   60 KT  70 MPH
 48H  25/1800Z 20.3N  76.2W   55 KT  65 MPH...INLAND
 72H  26/1800Z 23.0N  80.0W   50 KT  60 MPH...OVER WATER
 96H  27/1800Z 25.5N  83.0W   65 KT  75 MPH
120H  28/1800Z 28.5N  85.5W   75 KT  85 MPH

8/23/12
9:00AM

Max Windspeed: 40mph | Direction: West 13mph |

Isaac has had an extremely interesting thing happen to it.  This happens on occasion but rarely does it have such a negative effect.  Dry Saharan air from the north entered Isaac and caused the central core to weaken.  At that time convection about 30 miles to the west of that core became stronger and Isaac developed a center about 30 miles to the west.  Unfortunately, this had a huge negative effect.  At that time models were pointing Isaac to curve before it hit Florida and move out to sea.  The below image is exaggerated slightly to show detail.

Tropical Storm Isaac track shift - BLUE line indicated projected path without central core regeneration. YELLOW line shows projected path after Isaac's core shifted to the west.

Below are where you see the dark blues is the core of Isaac.  You can see how at the beginning it wasn’t well defined.  Now it’s becoming more defined.

Tropical Storm Isaac Water Vapor

Below is a graphic of a very likely path (red line) of Isaac.  This path would cause the most damage monetarily because the hurricane force winds would stay over the west coast of Florida while the core stayed over the Gulf sucking in hot ocean waters.  It would then continue northward and hit in the general area of Pensacola, Florida.  That is still a week away if that scenario happens though.

Tropical Storm Isaac's Projected Path

Below are current models of Isaac.  There is strong agreement with the general path now of Isaac.

Tropical Storm Isaac Models

The main problem with forecasting Isaac is that it’s an extremely weak storm at the moment and it’s going over islands which affects strengthening.  Stronger storms are much easier to predict.  Weak storms can change their course much easier.

Below is the 8AM National Hurricane Center forecast.  The cone is from 5AM though.

Tropical Storm Isaac 8AM Cone

If you live in South Florida, you should experience very strong winds from the south and south east starting Sunday night.  Make sure the southern portions of your house at the very least have shutters.  Winds will be strong enough to cause projectiles to break windows.

FORECAST POSITIONS AND MAX WINDS

INIT  23/0900Z 15.3N  64.0W   35 KT  40 MPH
 12H  23/1800Z 16.2N  65.9W   40 KT  45 MPH
 24H  24/0600Z 16.9N  68.4W   50 KT  60 MPH
 36H  24/1800Z 17.8N  71.1W   65 KT  75 MPH
 48H  25/0600Z 19.1N  73.4W   55 KT  65 MPH
 72H  26/0600Z 21.8N  77.4W   60 KT  70 MPH...INLAND
 96H  27/0600Z 24.4N  80.9W   65 KT  75 MPH...OVER WATER
120H  28/0600Z 27.4N  83.7W   70 KT  80 MPH

8/22/12
12:00PM

Interesting things have happened as of 11AM EDT. The NHC has reversed their track to the west now based on Hurricane Hunter data and radar data from Martinique and Guadeloupe Islands. The new data is suggesting a slight jog to the west. But again, plotting before tomorrow afternoon is subject to wild swings in projection. Models have also shifted slightly to the west. The biggest problem with long-range projections is you’re talking a distance of 100 miles over 6 days which is an error of only 16 miles per day (which is nothing). On the plus side, if Isaac does follow the path that NHC says as of now Isaac will barely be a hurricane if it hits Florida due to the amount of land it will go over. All of Florida should be preparing in these next few days. Even if Isaac doesn’t hit directly, strong winds can knock out power Monday into Tuesday.

The slight change in cone is due to the fact that Isaac is having trouble developing.  At one point Isaac lost its center and the center redeveloped slightly to the west.  This redevelopment is impossible to forecast and caused all data to shift to the west slightly.  Dry air from the north was injected into the core of Isaac causing the central collapse and reformation.

Tropical Storm Isaac Cone

Below are current models for Isaac based on the new data that Isaac has shifted to the west and reformed its core.

Tropical Storm Isaac Models

FORECAST POSITIONS AND MAX WINDS

INIT  22/1500Z 15.9N  59.3W   40 KT  45 MPH
 12H  23/0000Z 16.3N  61.8W   45 KT  50 MPH
 24H  23/1200Z 16.8N  64.8W   50 KT  60 MPH
 36H  24/0000Z 17.3N  67.8W   60 KT  70 MPH
 48H  24/1200Z 17.8N  70.3W   75 KT  85 MPH
 72H  25/1200Z 19.5N  74.5W   60 KT  70 MPH
 96H  26/1200Z 22.5N  78.5W   60 KT  70 MPH
120H  27/1200Z 25.5N  81.5W   70 KT  80 MPH

8/22/12
9:00AM

More models are starting to show Isaac missing Florida to the east.  Below are 3 main models used.

Isaac GFS Model

 Above is the GFS Model.  The GFS is the main model used and it shows Isaac over Florida on Monday.

CMC Isaac Model

 Above is the CMC Model (Canadian).  The CMC is showing Isaac curving out to sea before it reaches Florida.

NOGAPS-NAVY Isaac Model

 Above is the NOGAPS Model.  The NOGAPS  model  shows Isaac also curving out to sea.

Tropical Storm Isaac Models

Here are plots of combined models which show the majority of models now showing Isaac will turn to the north before it hits Florida.

Tropical Storm Isaac NHC Track Cone

Above is the National Hurricane Center’s forecasted track for Isaac.  Their track has shifted ever so slightly to the right (east) over the past 15 hours.  It’s looking as if this shifting to the east will continue over the next day or two.

Tropical Storm Isaac satellite image

Above is the current satellite infrared image of the Caribbean showing Tropical Storm Isaac and its distance from Florida.

Currently, Isaac only forecast to become a Category 1 Hurricane near Florida around 90mph.  This is a decrease from yesterday when it was forecasted to be around 110mph.  This is due to the more northerly path Isaac is forecasted to take which will take it over more land, thus decreasing the windspeeds slightly.

INIT  22/0900Z 15.5N  57.3W   40 KT  45 MPH
 12H  22/1800Z 15.9N  59.7W   45 KT  50 MPH
 24H  23/0600Z 16.3N  62.8W   55 KT  65 MPH
 36H  23/1800Z 16.8N  65.7W   65 KT  75 MPH
 48H  24/0600Z 17.3N  68.4W   75 KT  85 MPH
 72H  25/0600Z 18.8N  73.2W   65 KT  75 MPH...OVER WATER
 96H  26/0600Z 21.8N  77.1W   65 KT  75 MPH...OVER WATER
120H  27/0600Z 24.8N  80.0W   80 KT  90 MPH