28 July 2014

Tropical depression may be forming in eastern Atlantic

An easterly wave that exited the African coast on July 25 is now located about 1900 miles east of the Windward Islands and moving west at 12mph.  Unlike the last contender, the environment ahead of this one will be more favorable for development.

Visible satellite image from 7:45am EDT.
It will continue tracking to the west over the next 5 days, and be approaching the Leeward Islands on Saturday.  It's too soon to say anything specific about the intensity, but it is expected to become a Tropical Depression and then a Tropical Storm within the next few days.  Once it's an established tropical cyclone, models will have a better grasp on its forecast.

This disturbance is far enough south that the bulk of the Saharan Air Layer (mid-level, dry, dusty air that flows from Africa and sometimes all the way across to Cuba, Florida, and Central America) is located to its north.  The SAL is currently weak over the Lesser Antilles.

Depiction of the SAL today... the dustier areas are darker red, while areas not affected by the SAL are blue. The easterly wave of interest is in the lower-middle part of the image. (CIMSS and NOAA)
As I mentioned last week, this is about the time we start paying closer attention to the far eastern Atlantic for hurricane embryos.  Most hurricanes, and especially major hurricanes, have their origins as African easterly waves.  This period begins in late July and typically lasts through mid-October.

An example of a very intense hurricane that began as an easterly wave in late July and became a tropical depression almost exactly where this disturbance is located now is Allen (1980).  In the track map below, Hurricane Allen is plotted.  The gray circle in the far lower right corner is where the current disturbance is located today.  Hurricane Allen became a Category 5 storm three separate times (for a total of 72 hours), peaking with sustained winds of 190mph, and is still the strongest hurricane on record in the Atlantic.

Track and intensity of Hurricane Allen (1980).  The current easterly wave of interest is located at the gray circle. (NOAA)

22 July 2014

Tropical Depression 2 fighting a losing battle

The tropical disturbance I wrote about yesterday is now Tropical Depression 2... my update today can be found on the Washington Post's Capital Weather Gang blog:

Tropical Depression Two fighting a losing battle