First Rains in Dakar on August 5th!! -- African Easterly Waves picking up

Finally the first rains fell on Tuesday afternoon and evening in Dakar!!  The first rains should have begun in late June but did not.  We have another 5-6 weeks of rainy season left for the country and need abundant rain for farmers to post decent yields.  Overall conditions are not looking good for daily rainfall, but there are some positive events on the horizon.  In particular, the regular 3-5 African Easterly Waves (AEWs) have been picking up, this week.  One wave passed to the south of Senegal yesterday but was not able to produce any significant rain in Senegal because too much dry air is in place.  This first wave may develop into a tropical disturbance later this week over the Eastern and Central Atlantic.  The atmospheric sounding from today, suggest very strong winds (50 knots) at 10000-12000 feet which provides a vorticity sources (spin) to areas of the south.

Atmospheric Sounding from Dakar, Senegal on August 10, 2014

The dry air, which has its source over the Sahara provides and environment which is very stable and not good for thunderstorm development.   Eventually thunderstorms with AEWs to fall apart.   An example is below which shows how the storms dissipate over Senegal once disturbance enters.

The lack of precipitation is not a bad thing because the disturbances moistens the air providing a subsequent wave with a better chance of producing rain.   A second AEW over Mali today will likely bring rains to Senegal  tonight and tomorrow and this one also has the possibility of developing into a Eastern or Central Atlantic.

Precipitation Rates over West Africa, 8 PM Local August 10 2014 (heavy rain in Red)

A third wave is expected to develop over Nigeria tomorrow.

WRF Forecast at 10,000 ft  for Monday August 11

While it is likely that Senegal will have below normal rainfall this year, if the waves line up over the next 2-3 weeks, there may be abundant rain and the dry winds from the north may subside leading to an increase in local rains.    We have to hope for the best at this point as there another 30 days left in the rainy season.