MiamiensisWx wrote:The following post is NOT an official prognosis.There is a broad surface trough in the vicinity with minimal shear at the mid to upper levels. The westerly wind vectors from the low levels to upper levels denote the existance of the surface trough. No LLC is present or evident, but increasing UVV (Upward Vertical Vorticity) and 850 mb low level vorticity will likely contribute to the gradual development of a closed low level circulation within the next 24-36 hours. A mid level circulation is present. Divergence (providing ascent for additional convection) and diffluence (broadening of surrounding wind fields) is excellent, and capping/SAL is negligible in the vicinity. The presence of the adjacent tropical wave axis is contributing to good low level convergence as well. SSTs and OHC (ocanic heat content) are sufficient for additional development, though the best OHC is further west closer to the eastern Caribbean islands and Lesser Antilles. Overall, I anticipate slow initial development, and a TD will likely be classified within the next 2-4 days. I do not expect classification today or tomorrow, which is the short term. I believe development of 94L is very likely.
With the very favorable environment in regards to synoptics and thermodynamics, the islands should closely monitor 94L. A strong low level ridge will likely result in a southerly track toward the SE Caribbean/Windward Islands if the system develops. Since the environment will be favorable for gradual development and deepening of the surface low, I suspect that 94L could become a tropical storm prior to reaching the islands, with the most significant intensification occurring closer to the Windwards (as opposed to further east near its current location). The islands and Caribbean should closely monitor 94L over the course of this week.
http://www.ssd.noaa.gov/goes/flt/t2/loop-vis.html
The following post is NOT an official prognosis.Organization is continuing to increase, with the ascent provided by divergence resulting in additional development of thunderstorms. The boundary layer is clearly very unstable as well, and 850 mb low level vorticity remains abundant. Low level inflow is excellent on the southern side. It appears that the formation of a low level circulation may be gradually starting to occur near 11 N between 36-39 W. With minimal shear and ideal divergence/diffluence providing good "ventilation", a TD classification tomorrow is nearly certainly inevitable based on organization trends. Although the aforementioned location of the plausible LLC formation overnight is slightly further north, I personally believe it will exert minimal influence on the long term track of the budding TC. I'll explain my reasonings in the next paragraph.
As TS Bertha weakens and becomes more shallow, it will leave a weakness in the low level ridging over the next four to five days as it slowly moves NE and ENE from its current location. As I previously mentioned, the cutoff upper low to the east of Bertha at H5 (500 mb) will move SSE and amplify the H5 upper level ridging to the south and west. The key is 94L's intensity. It appears that 94L (as I suspected for a few days in my mind) will likely become deeper and more intense earlier than progged by the operational GFS, GFS ensembles, Euro, and other models in the short term. Additionally, based on the upcoming pattern and environment ahead of the system, a gradual and steady intensification trend is probable until 94L reaches the islands. I will not speculate on the intensity beyond that point. The trend implies that 94L (future Cristobal) will be more influenced by the mid to upper levels earlier in its life. 94L will likely become a TS over the next two to three days, and I believe it may approach the intensity of a strong TS as it arrives near the eastern Caribbean islands. The evidence strongly suggests that 94L will be deeper and influenced by the mid to upper levels. The weakness in the low levels will likely only result in a mild poleward movement of the LLC before it reaches the islands, followed by a WNW turn as the mid to upper level ridge develops over the Caribbean basin and eastern CONUS. Additionally, while it is initially weaker, it will move generally west because of the strong low level subtropical ridging to its north, which is producing easterly trades. When 94L reaches the eastern Caribbean, a faster movement toward the WNW is also probable, especially since the easterly trade speed max (strongest Caribbean trades) climatologically occur during July and August. We witnessed this factor with Dean and Felix in which case the strong easterly winds from the lower levels to upper levels resulted in a faster westward movement when they moved under the upper level ridge.
In summation, 94L poses a significant threat to the eastern Caribbean islands. If 94L is weaker throughout the short term and when it reaches the islands, a more NW track is probable toward the Leewards before the system turns to the WNW as it deepens. If 94L is stronger during this period as I expect, a more southerly and "subdued" track toward the northern Windwards, with a brief NW movement near the islands. This will be followed by the turn to the WNW. I believe the latter scenario is more probable, but even the fringes of the system can affect the Leewards and adjacent areas. All interests in the eastern Caribbean should closely monitor 94L, as it will likely approach strong TS intensity as it reaches the Lesser Antilles.
http://www.ssd.noaa.gov/goes/east/tatl/loop-vis.htmlhttp://www.ssd.noaa.gov/goes/east/tatl/loop-avn.htmlThis post is for the islanders.
