Friday, October 4, 2013

In-Depth Tropical Update: Karen

Tropical Storm Karen has weakened a little this morning due to dry air infiltration and moderate wind shear.  Karen currently is maintaining sustained winds of 60 mph and a minimum central pressure of 1003 mb.  The weather model spaghetti plot continues to show a decent spread in possible landfall locations.

Model Projections through 6 AM Wednesday

A decent cluster of models continue to show a significant turn to the NE with a possible brief landfall in Plaquemines Parish in extreme SE Louisiana.  It would then continue towards the Alabama or Florida coast.  There are still several models still indicating a landfall along the central Louisiana coast.  So what are these models seeing?  Well the left sided cluster is indicating a weaker Karen that will move faster to the north.  This will not allow an approaching trough and cold front from picking it up and carrying it farther east.  If this were to occur the worst South Louisiana and metro Baton Rouge would see would be sustained winds of 25-35 mph with higher gusts.  Rainfall totals of 2" would be possible too.  This would only last for about 12 hours.

Current position of possible steering currents.
What we expect, along with the National Hurricane Center, is that Karen will at a minimum keep it's current strength if not strengthen slightly.  Karen is no longer expected to reach Category 1 hurricane status.  Karen is also forecasted to slow down today and tomorrow.  This would allow time for the trough to move close enough to steer Karen farther to the ENE.

Forecasted position of steering currents very early Sunday.

Think of the trough or front as a blocking mechanism.  Karen will then get picked up by the trough and move quickly NE towards Alabama and Florida. 

So what can South Louisiana expect with this forecast.  Tropical storm forced winds will be anticipated late Saturday into Sunday along the extreme SE coast of Louisiana.  This would be more or less for the New Orleans area, St. Bernard,Terrebonne, Lafourche, and Plaquemines Parishes.  We can also expect to see some storm surge in these areas too.

Storm surge projections from National Hurricane Center
The National Hurricane Center is projecting a large swath of 2-3 feet storm surge from SW Terrebonne Parish east to LA / MS state line.  The Southern part of Lake Pontchartrain is also included.  A smaller swath of 3-5 feet surge would occur on the North Central part of Plaquemines Parish.  Storm surge measures as such: if you put your toes right on the current water line of the bank or beach depending on your coastal location you would then see a rise in the water level based on the projection.  The timing of this surge potential would be late Saturday into Sunday as the storm approaches.  Once the storm passes the winds will shift pushing the water away from the coastal land areas.

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