01 August 2012

Easterly wave nearing Depression strength

The easterly wave that exited the African coast on July 26 (and spawned over the Ethiopian Highlands around July 19) has been slow to get organized, but is decidedly doing so.  It is now a 1009mb Low centered near 11N 47W, or roughly 950 miles east of the southern Windward Islands.  Maximum sustained winds are estimated to be 30kts. It will be another couple of days until it's within aircraft range and we can get an accurate assessment of the intensity.

The graphic below shows vertical shear streamlines (in white) and magnitude (in yellow) overlaid on an infrared satellite image.  Some of the shear is generated by the anticyclone over the system itself, and can be discounted, but there is most definitely a net strong westerly shear impinging on the northern edge of the system.  It should remain south of that subtropical jet and in a favorable environment for further development.

The SSTs under it and along its trajectory are around 28C (+/- 0.3C), which is more than ample to sustain a strong storm.  The ocean heat content (a measure of the thermal energy of the ocean integrated from the surface down to the depth of the 26C isotherm) will be increasing with time though, which means there is warm water well below the surface, and a decreased chance of mixing and upwelling being a negative factor in development.

Now on to the model guidance.  Basically every model is forecasting intensification and a continued W-WNW motion over the next 5 days.  This will bring the storm over the Lesser Antilles by late Friday into early Saturday, likely as at least a strong tropical storm.  Being so far south, there's a remote possibility that it will hit South America and dissipate, but the greatest odds are for a track along the length of the Caribbean.  Stay tuned!

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