21 July 2014

Disturbance in central Atlantic a sign that Africa is waking up?

We are getting into the point of Atlantic hurricane season when we start to shift our attention far eastward to look for hurricane embryos.  From early August through mid October, many of the tropical cyclones that form can be traced back to easterly waves that are created over continental Africa.

Today, an easterly wave is located about 1300 miles east of the Lesser Antilles and has slowly been getting better organized since exiting the African coast last Thursday.

While the disturbance currently looks like it is on its way to becoming a bona-fide tropical cyclone, the environment in which it's embedded is far from hospitable.  The low-level air nearby is dry and dusty, courtesy of a huge plume of African air called the Saharan Air Layer... it's fairly normal to have this plume spanning the deep tropics this time of year.

Today's analysis of aerosols in the atmosphere.  While there are a variety of naturally-occurring aerosols,  the ones of interest here are dust particles from the Sahara Desert. The disturbance's approximate locatation is marked with a red dot. (NRLMRY)
Another factor working against it is dry air in the middle and upper parts of the atmosphere, as seen in this water vapor image.

Water vapor image showing dry air in browns and moister air in grays and brighter colors.  The disturbance is positioned in the lower right.  (NOAA)
However, for the next couple of days, the vertical wind shear is expected to remain relatively low, and the sea surface temperature under it is marginally high enough to sustain a tropical cyclone.  So it does stand a chance of forming if it does so soon.

If it should eventually reach tropical storm status, the next name on the list is Bertha.  Bertha is still one of the original names from the set of six lists started in 1979.  It was first used in 1984, so this year will be its sixth time around.  This is a total coincidence, but Bertha 1996 was also located very close to where this system is now, and it ended up becoming a Category 3 hurricane north of Hispaniola and making landfall on North Carolina as a Category 2 storm on July 12.

Hurricane Bertha in July 1996.  The gray circle in the lower right shows where the current disturbance is located.  (NOAA)

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