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T.D. #6 Becomes "Fernand"

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Updated: 8/25/2013 7:02 pm
Tropical depression #6 has quickly intensified into tropical storm "Fernand".  
This system has everything going for it EXCEPT an imminent encounter with Mexico. Shear is light...waters are warm & the atmosphere is moist. The system is being steered by a large & strong upper high (3rd image below) across the U.S. insuring that the system continues west into Mexico.  There is no threat to the First Coast or any of Fl.

Meanwhile...the tropical wave/surface trough of low pressure over the far Northern Gulf continues to produce heavy but very disorganized t'storms.  Its short time left over warm water + 20-30 knots of shear should limit much substantive development as the disturbance moves west.

And yet another tropical wave is over the Central & Northern Caribbean moving west/northwest.  No development of this wave is likely through at least the short term but forecast models did not seem to initialize this wave well.  I feel this is a wave to watch in the longer term -- NW Caribbean/W. Gulf.

We'll need to carefully monitor an unseasonable yet weak front/trough that will settle into the Gulf of Mexico eastward across Fl. into the SW Atlantic this week.  Forecast models do not show low pressure developing at this point anywhere along the front, but this is a potential classic set-up where a cluster of t'storms becomes established then develops low pressure & becomes a tropical system.  Just something to keep in mind...

Check out the very strong upper level high over the nation's midsection which will be a major "driver" of any tropical disturbances in the W. Caribbean & Gulf.  The tendency will be for upper level troughing to develop to the east of this big high -- over or near the U.S. east coast -- which would play a role in any tropical disturbance moving west or northwest from the open Atlantic (east of Fl.).

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 in the short term.

Most 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 a remaining "pinched" trough in the W. Atlantic might play a role in any possible movement across the Atlantic....or lack thereof.

Shear remains strong over much of the Atlantic Basin -- as can be seen below -- exceeding 30 knots over parts of the Caribbean...exceeding 30 knots over the Central Atlantic...and 50+ knots over the E. Atlantic.

The frequency of tropical waves moving off Africa is increasing but still lacks much organization.  While no significant development is likely in the short term, this is an area that could -- & should -- become quite active in the next 1-3 weeks.  Disturbances & low pressure moving across tropical & subtropical Africa are becoming quite numerous & more impressive with time.

Velocity potential anomalies 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 & now the Gulf & Caribbean.  We’re probably looking at about the end of Aug. & first couple weeks or so -- at least -- of Sept. for the Atlantic to become more active.

Speaking of the E. Pacific (& related to the vertical velocities mentioned above)..."Ivo" is moving west of the Baja of California producing heavy rain, gusty winds & rough surf.  Moisture from what's left of "Ivo" will spread into the SW U.S. increasing heavy rain & the flooding threat for parts of S. Ca., Az., Utah & NM.

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