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Shear & Dry Air Continues to Tame "Karen"

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Updated: 10/04/2013 9:08 pm
Poorly Organized "Karen" In the Central Gulf....... 

- given the forecast thinking/reasoning (as discussed below), local impacts will -- generally -- be relatively minor
-- Sat. will be nice....showers & scattered t'storms will increase Sunday through Sun. night, but it's not looking like a washout with storms continuing into Mon.
-- an isolated threat for tornadoes favoring western parts of the viewing area (Lake City to Waycross) but at least some threat for Jacksonville & the rest of NE Fl., SE Ga.
-- some heavy rain but speed of the system + a track to the west/northwest of Jax should limit the overall amounts -- perhaps an average of a half inch to an inch, locally 1-2" especially west & northwest of Jax. 
-- breezy Sunday-Sun. night & to some degree Mon. but not overly strong averaging 15-25 mph.
-- somewhat rough seas & surf Sunday-Mon. but again relatively minor.  An offshore component to the winds by Mon. will make for happy surfers(!).

While there has been occasional strong convection near the center with brief attempts at wrapping around the center, the center has generally been clearly exposed -- even in infra-red imagery -- to the west of the convection.  It's questionable as to whether or not the center can ever truly become imbedded underneath the strong convection thereby allowing the mid level & low level center to become stacked.  A stacked system would be at much higher risk of intensifying.

Sea surface analysis below.  The numbers show the wave heights with the highest numbers closer to "Karen", of course.  Higher waves/rough seas & surf & a high rip current risk will affect the Fl. Panhandle coast through the weekend.  Wave heights will not be significant for the First Coast.

Satellite imagery shows a struggling "Karen" thanks to moderate west/southwest shear.  The center is clearly displaced to the west of the strong convection as mentioned above.  The track has generally been a little west of earlier forecasts, but the end results should be similar to previous expectations.  The central pressure steadied Fri. after rising most of Thu. night.  I do question whether or not "Karen" will be able to truly reorganize & strengthen given its current poorly organized state on satellite imagery.

The storm continues to be tamed by persistent west/southwest shear.  The shear will relax a bit through Sat. but will still likely be at least 15-20 knots.  The question becomes whether or not the storm can reorganize given the messy appearance on satellite imagery + the relatively short time over warm water Sat.-early Sun. before landfall. Water temps. are more than warm enough to support a tropical cyclone, but the shear as well as dry air will be something "Karen" will have to consistently battle.  Some organization is possible upon approach to the coast due to interaction with a cold front & approaching upper level trough.  The primary intensity issues: 

(1) very dry mid & upper level air (as can be seen on the water vapor images below - the black & rust color) over Mexico & virtually all of the western half of the Gulf of Mexico extending north into the Southern U.S.  This dry air may ultimately be the most significant hurdle for "Karen" to overcome as the dry air will remain adjacent to the storm all the way through landfall.

(2) the moderate to quite strong shear over the Gulf will abate some through Sat. night before increasing again Sun. as an upper level trough approaches.  So we'll have to watch the system carefully over the weekend to see if the slightly lighter shear allows for some organization.

In addition... as the upper level trough moves into the Eastern U.S., there might be some "ventilation" (diffluent flow aloft) of "Karen" upon approach to the Gulf Coast which could compensate for the increasing shear & dry air, thereby at least maintaining the storm or even allowing for some increase.  It will not take long for "Karen" to transition to an extratropical low pressure area moving northeast along the cold front Mon. & Tue.

The timing & how far south this upper trough digs will be the main driver for the track of "Karen".  A weak & transient upper level ridge will build north & northeast of the storm through Sat. over Georgia & Northeast Fl.  As the trough approaches, the ridge will collapse paving the way for the northeast acceleration of "Karen" Sun.-Mon.  The system will then become attached to a cold front & absorbed by the upper trough over the Eastern U.S.  The timing -- landfall -- of "Karen" has generally slowed which is no surprise since the upper level trough is strong & still deepening.  In such a scenario, a slower evolution of weather systems usually evolves until the trough has completed the deepening process thereby slowing the "hook up" with the cold front.

Atmospheric data gathered by hurricane hunter aircraft + research planes were inputted into the forecast models Thu. night.  Interestingly....according to the NHC after using radar imagery for the HWRF model:
The GFS forecast model has now joined the model "camp" that's keeping "Karen" weaker.  While more similar to some of the other global modes, the GFS is still a little farther east but is pretty much in line with a slower move to the coast. The European forecast model continues to be weaker but is now only a little farther west.  Overall....these 2 models -- which I favor to forecast the tropics with -- along with most of the other global forecast models have come into relatively decent agreement on a weak to low end moderate tropical cyclone making landfall later Sunday-Sun. night after grazing extreme SE Louisiana late Sat.  But since "Karen's" structure is so poor, there has been a more westward track initially.  

So....  I favor "Karen" moving to the Gulf Coast somewhere between approximately Pascagoula & Apalachicola about Sunday, perhaps as late as Sun. night.  BUT there could be some interaction with extreme Southeast Louisiana as early as late Sat./Sat. night then the center would hug the Gulf Coast or hang just offshore while moving east/northeast before turning more sharply northeast upon feeling the effects of the upper trough/surface cold front.  We'll have to watch the recent eastward trend in the models for the "end game" as a move inland closer to the Big Bend will be possible but for this to happen, there need to be a very sharp eastward turn.

If traveling this weekend west to the Fl. Panhandle &/or coastal Mississippi/Alabama, stay up to date on "Karen".  Heavy rain & gusty winds....& possibly isolated tornadoes.... will be most significant from about the Fl. Big Bend across the Panhandle to as far west as near/just east of New Orleans.  And, of course, remember that the ultimate track & intensity is subject to change(!).  There will also be a corridor of potentially enhanced heavy rain & isolated tornadoes across Georgia into the Carolina's near & just east & south of the track of "Karen" or its remnants Sun.night-Monday.

Click ** here ** for buoy reports from the Gulf of Mexico.

The image below shows the moderate -- 20(+) knots -- over a good portion of the Gulf of Mexico.

Water vapor satellite images below showing the vast area of very dry air in close proximity to "Karen":

Model plots + radar imagery (with projected track of "Karen") below courtesy S. Fl. Water Management District:

Tropical waves continue to decrease as they move off the coast of Africa. This late in the season, development -- or at least long track tropical cyclones across the Atlantic -- is not common so deep in the tropics.  Still...these waves would have at least some potential for long term development if they can get across the Atlantic near the Caribbean &/or SW Atlantic.  There remains potential for long term development in or near the Caribbean & SW Atlantic in roughly 10 days to 2 weeks.

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