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Northern Gulf Storms

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Updated: 8/23/2013 6:44 pm
T'storms N. Gulf.....

Very disorganized t'storms continue over the Northern & Northeast Gulf of Mexico.  Weak low pressure might evolve just off the Gulf Coast but any tropical development would be slow, at worst.  As upper level high pressure -- & more importantly (because the system is weak & shallow) -- as surface high pressure moves to the U.S. east coast (see map below, 3rd image), the Northern Gulf disturbance will be steered to the west away from Fl..  

A weak tropical wave & surface trough of low pressure continues to produce t'storms in the Western Caribbean.  Movement will be to the W/NW into Central America with little development expected.

Large areas of dry mid & upper level air (black & rust colored areas on the water vapor satellite image below) remain over the Central Atlantic. Overall conditions remain unsuitable for significant tropical development as shear generally remains high too. In addition, a large upper level trough is over the W. Atlantic.  This trough is expected to slowly weaken & lift to the north but a piece of it could be left behind next week & reinforced by another upper trough that will move in from the west.  This scenario might be something to watch for gradual tropical development in the long term.

Some forecast models continue to point to tropical development in the far Eastern Atlantic during the last few days of Aug. & especially into Sept.  The troughing (or possible reinforcement of the trough) or remaining "pinched" trough might play a role in any possible movement across the Atlantic....or lack thereof.

Shear has lessened over the Central/Southern Gulf of Mexico but is still strong over much of the Atlantic Basin -- as can be seen below -- exceeding 40 knots over parts of the Caribbean...exceeding 30 knots over the Central Atlantic where a large upper level trough is positively tilted north of the Greater Antilles....

The frequency of tropical waves moving off Africa is increasing but still lacks much organization.  While no substantive development is likely in the short term, this is an area that could -- & should -- become quite active in the next 1-3 weeks.

Last week I mentioned the MJO looked like it was getting way to kick in which could lead to an increase in tropical activity in the Atlantic.  Velocity potential anomalies are related & can give us a clue to when there might be an uptick in tropical cyclones.  The map below shows upward vertical velocities (rising air) in the green area – look how nicely this correlates with thunderstorm clusters that can be seen in IR satellite imagery superimposed on the map.  The brown lines represent sinking air which is not as conducive to convection & tropical development.  The large area of positive vertical velocities will gradually spread eastward, & we're already seeing an increase in the vertical velocities over the Central & E. Pacific with tropical development just west of Mexico.  We’re probably looking at about the end of Aug. & first couple weeks or so of Sept. for the Atlantic to become more active.

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