Tropical weather analysis - June 24, 2010

Began writing at approximately 8:58 PM eastern

Invest 93L has become much better organized this evening. Infrared satellite loops indicate that convection, while not quite as cold as it was earlier, continues to expand. The improving surface center appears to be centered along the extreme northern edge of the deep convection, as per various satellite animations. I place the center at 16N 80W. CIMSS analysis depicts about 20 kt of northwesterly shear impinging over the system, emanating from the eastern extent of a well-defined upper-level anticyclone currently centered several hundred miles east of Honduras. This likely explains the fact that the center is not fully embedded within the deep convection.

Water vapor loops show that any dry air currently present to the west of the system is quickly mixing out, and I am not expecting dry air to be a problem for 93L in the near-term. Low-level convergence and upper-level divergence associated with the system are currently rather meager. This, along with the moderate northwesterly shear that the system is currently experiencing, should limit any rapid development in the near-term, though I do expect a gradual consolidation of the system for the next 12 hours. The GFS suggests that the anticyclone will move northward toward the Yucatan Channel beginning in about 18 to 24 hours.

By this time, 93L should be nearing that area, and so should this forecast transpire, 93L will have ample opportunity to develop into a tropical depression tomorrow. A reconnaissance aircraft is scheduled to investigate the system tomorrow, if necessary. The previous two flights have been canceled due to a lack of organization, but if current trends continue, I suspect that tomorrow's flight will be allowed to commence. This should provide us with valuable data that will allow the models, which have been doing rather poorly with this system -- what with the flip flopping and all, to initialize the system better, and hopefully more accurately predict both track and intensity.

There is currently a belt of very high wind shear, 40 knots in some areas, across the southern and central Gulf of Mexico. Both the GFS and ECMWF, our two most reliable models, foresee this shear lifting out as 93L enters the Gulf of Mexico in around 72 hours. Should this indeed happen, it would allow the system to intensify up until landfall along the western or northern Gulf Coast in about 132 hours. It should be noted, however, that the GFS no longer foresees an anticyclonic environment across the Gulf of Mexico, at least after the first day or so that the system enters the Gulf. This would allow 93L to be highly vulnerable to any vertical shear. We will see how this goes.

Right now, conditions appear favorable enough for a tropical depression to form within the next 24 to 36 hours, and then eventually to a minimal hurricane as the system traverses the central Gulf of Mexico. Curiously, the ECMWF is rather slow with this system, delaying the time of landfall along the Gulf Coast full 24 hours in comparison to the other models. It could be picking up on a possible collapse of steering currents in about three to four days as the system traverses the Gulf of Mexico. Out of respect for this possible scenario, as well as the fact that the ECMWF is a rather well-performing model, I will forecast a landfall along the northern Gulf Coast in 132 hours.

It also doesn't show a landfall along the Yucatan Peninsula until 72 hours, while the other models show 48 hours. I will once again split the difference here and forecast a landfall along the eastern Yucatan Peninsula in around 48 hours. After landfall in the Yucatan Peninsula, the system should enter the southern Gulf of Mexico by around 72 hours, at which point a strong upper-level trough approaching from the west will begin moving the system more poleward. Right now, I don't think any of the models have a particularly good handle on the eventual track of this system, though I suspect that 93L will make landfall somewhere along the western or central Louisiana coast in five days.

However, this is far from certain, especially pending recon data, so residents all along the Gulf of Mexico, particularly from Galveston to Pensacola, should carefully monitor the progress of this system over the next several days.

Interestingly, the 18z GFDL and HWRF do not make the system a tropical cyclone throughout the forecast period, and instead bring it to the northern Gulf Coast as a sheared system with 25 kt winds. This is considered highly unrealistic for now, in light of what was said above.