24 July 2012

Two disturbances scattered across the basin

After a long hiatus of activity in the Atlantic, things are picking up... including the first healthy easterly wave coming off of Africa, a sign that the heart of hurricane season is upon us.

First, there is a small but well-organized circulation in the north-central Atlantic that could be rapidly approaching tropical storm status.  Located near 37N 54W (roughly 700 miles south of Newfoundland), it's headed slowly toward the northeast... away from any land.  Model guidance suggests that this system could intensify slightly in the next 1-2 days, then weaken as it heads over much colder water.  If named, it would be Ernesto.

The second feature of interest is a large easterly wave that existed the African coast earlier today.  This wave can be traced back to its origins over the Ethiopian Highlands on July 17... it has been a persistent disturbance during its entire week-long trek across the African continent.  [One handy way to track these easterly waves is via a Hovmoller diagram... in this case a time-longitude plot.  http://andrew.rsmas.miami.edu/bmcnoldy/tropics/hovmoller/  You can choose the sector of interest, and see a sequence of infrared images composited every 12 hours for one week.]

The image below shows an infrared image overlaid on a derived product depicting the "Saharan Air Layer" (SAL) which is characterized by fine dust particles and relatively dry low-to-mid-level dry air from the Saharan Desert.  While the majority of the basin is covered with this convection-squashing air (shown by the yellow/orange/red shading), the region where this easterly wave is located is somewhat conducive for development.  However, as it moves west, the environment may become less conducive... and the majority of long-range global models do not develop this wave.  It is still somewhat early for the "Cape Verde season", but it's not far off.

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