Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.
By: KoritheMan , 1:13 AM GMT on October 22, 2011
An area of disturbed weather over the western Caribbean ("96L") is a threat to develop into a tropical depression. Last light visible imagery showed a small but fairly well-defined circulation, although, due to a lingering upper trough to the north, there is evidence of northwesterly shear inhibiting outflow to the east.
Figure 1. Latest infrared satellite image of Invest 96L, courtesy of NOAA's Satellite Services Division (SSD).
The current northwesterly shear notwithstanding, upper-level winds are forecast to remain conducive throughout the forecast period. This should allow for 96L to continue to organize, and I expect we will have a tropical depression in about 36 hours.
The dry air that was plaguing the system yesterday has abated, and there is little reason to assume that 96L will not go on to become a tropical storm, and quite possibly a hurricane. Indeed, the GFDL and HWRF both bring this system to near Category 4 strength in the Yucatan Channel in five to six days. While I am not a model worshiper, conditions certainly appear conducive enough to support a major hurricane. Oceanic heat content is still extremely high in this region of the Atlantic, as it has remained virtually untapped.
Figure 2. Caribbean Sea Tropical Cyclone Heat Potential (TCHP) as of October 20, 2011. Values of 80 and above are considered to be conducive to rapid intensification.
I am not ready to call for a major hurricane just yet; caution dictates waiting another day or two, to see how the synoptic pattern evolves. However, interests across the entire western Caribbean should carefully monitor the progress of this disturbance, as things have the potential to get ugly, possibly sooner rather than later. It will likely still be in the Caribbean five days from now.
This system should move little over the next two days, with perhaps a slow northward drift. Thereafter, this system will likely continue moving generally poleward, ultimately threatening the Cayman Islands and western or central Cuba. On Monday, a trough is forecast to amplify over the western Atlantic. The models have varying depictions regarding the depth of this trough, but they agree that it will be too shallow to pick up 96L/Rina, leaving it trapped in a region of weak steering currents as high pressure attempts to build in to the north, but cannot due to continuous shortwave impulses riding the westerlies over the southern United States. By five days and beyond, a substantial cold front is forecast to dive southward and erode the ridge. This is where things get tricky, as the global models all have varying depictions regarding the exact placement of the trough axis, with some bringing the greatest energy over the central and southern US, while others keep it farther northward. The former scenario would favor a track into southern Florida, while the latter would favor a path north-northeast or northeast over central Cuba and out to sea.
Needless to say, there is a high degree of uncertainty concerning the future trajectory of this system. However, there could very well be a dangerous hurricane within the confines of the western Caribbean in the next several days, one that could eventually threaten the United States. I warned several weeks ago that things were not over.
A tropical wave located several hundred miles east-southeast of the Windward Islands ("97L") is no immediate threat to develop due to unfavorable vertical shearing conditions. However, these extremities are forecast to slowly relax over the next 36 hours. Thus, after that time, 97L could slowly develop as a broad anticyclone builds overhead. However, the GFS shear forecasts indicates that this anticyclone will probably not be as healthy as the one forecast to develop over 96L; it will also be short-lived. This makes sense given the expected interference from 96L.
This wave will probably not become a hurricane, and it might not even develop. However, many of the global models are indicating at least weak development as it passes through the Windward Islands and begins churning the eastern Caribbean waters.
Regardless of development, locally heavy rainfall and gusty winds will likely accompany this system as it moves through the Windward Islands over the next day or two.
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