Karen weakens, Lorenzo forms...

The much-anticipated vertical shear has finally met Karen head-on.  The low-level center is now displaced 3 degrees to the west of the deep convection and completely exposed, thanks to 25kts+ of westerly vertical wind shear (defined as the vector difference between the 850mb winds and the 200mb winds over the system).  The intensity has fallen to 55kts and 1004mb.  It's tracking WNW at 10kts, and the forecast is for heading NW and weakening/maintaining intensity.  However, after this confrontation with the trough (5+ days) Karen could warrant a much more cautious watch as a ridge moves over the storm and decreases the shear and steers it more toward the west.

At 18Z today, TD13 was upgraded to TS Lorenzo based on aircraft recon into the storm.  This is the twelfth named storm of the season, already above the long-term average of 10 for the season, and there are still 2 more months in the Atlantic hurricane season.  Lorenzo has become much more compact, with a very vigorous central core and CDO with cloud tops hitting -80C. 
The circulation is still visible from the Alvarado radar at http://smn.cna.gob.mx/radares/radares.html
The latest intensity is 50kts and 1004mb and it still appears to be intensifying.  The forecast brings it up to 55kts prior to landfall on Friday night.  The primary problem with this storm is the motion: almost none.  It is drifting at 2-3kts toward the Mexican coast, and in the meantime will begin to spread very heavy rain throughout central Veracruz and even further inland.

There's a new healthy tropical wave near the Cape Verde Islands (~25W) which exited the African coast on Tuesday.  Perhaps of more note is a wave still over land that should exit the coast tomorrow... that one is favored to develop quickly by several global models.

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Karen strengthening, TD13 forms...

Karen has made surprising strides in organization over the past 24 hours.  A struggling 35kt storm yesterday at this time, it's now a compact 60kt storm with a developing eye... nearly a hurricane.  It now has centralized deep convection, but the outflow is asymmetric owing to the westerly vertical shear.  The estimated central pressure is 990mb, and Karen is now  expected to reach hurricane strength later today.  It's moving WNW at 11kts, and that motion should continue over the next several days, perhaps becoming more NW at times.  The stronger vertical shear is still forecast to impinge on the storm late this week into the weekend, which could weaken it a bit, but by early next week, the trough will pass by and Karen might find itself on a strengthening trend again.
VIS satellite image of Karen: http://www.ssd.noaa.gov/goes/flt/t1/vis-l.jpg

The area of disturbed weather in the Gulf that I first mentioned on Monday has been upgraded to TD13, and is very close to being upgraded to TS Lorenzo.  Intensity is 30kts and 1006mb and is forecast to drift very slowly toward the west into Mexico as a strong tropical storm on Friday.  You can keep an eye on it from Alvarado's radar at http://smn.cna.gob.mx/radares/rad-alva.gif

The other area I was discussing before that was near Puerto Rico is now over the Dominican Republic: poorly organized and highly sheared.  However, as I pointed out yesterday, this should not be dismissed in the long term.  IF the circulation can survive the trip over Hispaniola, the hurricane "sweet spot" near the Bahamas could re-energize the system in a few days.

Lastly, a new area of interest has popped up off the southern Florida peninsula that warrants a close eye.  It is in an environment conducive for genesis, and this could track across the peninsula as a VERY rainy tropical storm.  If this does rapidly organize, the name/number on deck is 14/Melissa.
Radar image of this disturbance: http://radar.weather.gov/radar.php?rid=amx&product=N0Z&overlay=11101111&loop=no

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Karen forms in deep tropics...

At 03Z today, the tropical wave near 35W was upgraded to TD12, then to Tropical Storm Karen just six hours later.  It remains a minimal 35kt tropical storm now, and convection is fairly shallow and scattered.  The vertical shear is very low right now, but is forecast to become excessive by the weekend, halting any attempts at a significant hurricane for the next several days.  There is a buffer timeframe however, while the SSTs are warm and wind shear is low enough and before the subtropical jet comes in  and kicks up the shear, when the storm could reach hurricane intensity (or after crossing north of the subtropical jet in a few days).  It's located near 11N 40W and tracking WNW at 13kts.

Elsewhere, the other two areas of interest are still out there, but not in any rush to get organized.  The one near 65W is entering a high westerly vertical shear zone near the northern Leeward Islands, and has a slim chance of making it through intact. BUT, if it does survive the next 2-3 days, it would be one for Floridians to monitor in case it develops near the Bahamas.  And the third, now in the west-central Gulf of Mexico, is a 1009mb Low close to Depression status as it drifts very slowly to the west toward the Tampico area.  It's over 30C SSTs, in a low-shear environment, and could become TD13 later today or tomorrow.
VIS image of system near northern Leeward Islands: http://www.ssd.noaa.gov/goes/flt/t2/vis-l.jpg
VIS image of system in western Gulf of Mexico: http://www.ssd.noaa.gov/goes/flt/t4/vis-l.jpg

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