TAOI 07-21-2010

Overview:

3 PGI systems are continuing to be tracked today.  PGI-16L, PGI-17L (AL 97), and PGI-18L.  PGI-16L is emerging into the SW Gulf of Mexico from the Yucatan Peninsula at 20N, 90W.  AL 97 is located north of the Dominican Republic/Haiti border at 20N, 67W.  PGI-18L is located around 18N, 37W.  A tropical wave, separate from AL 97  is being analyzed by the OPC at 75W, just south of 18N.  Elsewhere in the Atlantic, a 1028 hPA high continues to dominate the lower levels and flow through the Caribbean, over Florida, and into the Gulf of Mexico continues to be out of the E or SE.  Looking at upper levels, an upper level low continues to persist northwest of of AL 98, while the upper-level low in the Gulf is moving over the Texas coast. 

Discussion:

AL97 showed signs of development yesterday afternoon, and ASCAT began to show signs of a circulation, or at least a turning of the winds.   However, overnight the convection dissipated and now appears very unorganized around the center of the invest location.  There is substantial convection still occurring to the southeast of the trough, south of Hispaniola and Puerto Rico, likely driven by the outflow of the previous convection to the north.  Shear remains high to the north of AL97 due to the influence of the upper level low.  However, the low is propagating east and around the same pace as AL97, meaning that the center continues to be located away from the highest shear.  It is worth pointing out that the center is more difficult to define today, due to the lack of ASCAT data, as well as the fact that almost no convection is occurring where the center has been analyzed.  On the other hand, SSTs remain high, and moisture is also high as shown in water vapor imagery and soundings from the Dominican Republic and Puerto Rico. While several models showed AL97 developing substantially yesterday, that is not the case today.  SHIPS and LGEM (with a high bias due to this not yet being a depression) still show the strongest development, however that is only to a tropical storm.  HWRF and the GFDL also show TS development, albeit briefly, before the system is downgraded to a depression.  However, even this development may be optimistic since those models require a bogus vortex, meaning that the initial condition does not necessarily reflect the actual conditions.  Most models take AL97 on a more southerly route today through the keys, and as development continues to be non-existent, a more westerly track seems reasonable.  It is worth noting that recent satellite imagery has shown an increase in convection near the center of AL97, but development is still not likely due to the lack of circulation, land influences, and the shear to the immediate north.  While development is not immediately expected within the next 24 hours, a tropical depression could form if the cold low moves far enough ahead of the trough that shear begins to decrease over the system.  Furthermore, if the system moves into the Gulf sufficiently far enough from the upper level low, it is also possible that development could occur there.

To the southeast of AL97, and area of convection has formed, seemingly originally from outflow boundaries related to AL97 yesterday.  While this area is not under the influence of any synoptic features, convection has managed to maintain itself over the past few hours.  Downflow ridging relating to the upper level low N of AL97 may be related to the sustained convection, however the ridge seems to be centered even farther downstream.  This convection has completely separated itself from AL97, and is not likely to influence the development, or lack there of, of AL97.  If convection persists for the rest of the day and overnight, there is a slight possibility of an MCS developing, which could eventually devlop into a system of interest.  HOwever, at this point it warrants nothing more than continued monitoring. 

The other waves in the Atlantic all show little to no organization or widespread convection.  Pouch tracking does not develop or strengthen any of these waves, and while they will continue to be monitored, they appear to demonstrate no risk of development.