31 July 2012

Disturbance slowly trekking westward

There is not a lot to update with regard to this disturbance, but for the sake of continuity, I'll include the latest information.

It's still a 1010mb Low moving W-WNW at 12kts, and is now located about 1400 miles east of the Lesser Antilles.  It's actually quite far south --9.3N at 12Z today-- which is keeping it somewhat removed from the drier SAL air to the north.  Over the past 12 hours, the deep convection has picked up near the center, which is likely a sign that it's ready to complete genesis and become a numbered system.  Most models do develop it, but rather slowly over the next several days.

The SST is still right around 28C and the vertical shear is (and will be) in the 5-10kt range.  It's still too early to seriously speculate on the long-term track of this system, but it is certainly something to keep a very close eye on.  Model guidance will improve once it's an established, trackable entity.

30 July 2012

Easterly wave showing signs of organization

An easterly wave that exited the African coast on July 26 is presently located near 9N 36W, or about 800 miles southwest of the Cape Verde Islands. There is a 1010mb Low embedded within the wave.

The Saharan Air Layer (SAL) that has dominated the basin for the past 1-2 weeks is weakening, and is mostly to the north of this disturbance. The sea surface temperature (SST) under the system is about 28.3C and will move over similar temperatures over the next several days.  Vertical shear is very low (<5kts) and is expected to remain low for the foreseeable future as it travels WNW at around 12kts.  If it remains intact, it would arrive at the Lesser Antilles by the end of this coming weekend.  Given the ideal environmental conditions, this disturbance will likely be quick to develop... the plot below shows several parameters from recent model runs (intensity, track, shear, SST, RH):

If named, the next name on the list is Ernesto.  Climatologically, the 5th named storm in the Atlantic forms on August 31.  For a bit of hurricane history, the infamous Hurricane Andrew was also a 1010mb Low almost exactly in this location on August 16, 1992.  Not that this will necessarily be anything like Andrew, but it is worth realizing that this is how even the greatest of storms have their beginnings.  Eight days later, Andrew would make its destructive Category 5 landfall just south of Miami FL.

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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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