Drought like conditions over Senegal and the Cape Verde Season for hurricanes

The evolution of El Nino during the spring and summer season suggested that rainfall would be below normal for much of the Sahel (the region just to the south of the Sahara).  During the month of June, the Saharan Air Layer (SAL) and several dust events were evident over the region.    Since 2005, the Laboratory for Atmospheric Physics-Simeon Fongang at Cheikh Anta Diop University in Dakar Senegal has partnered with Howard University to measure rainfall within 100 km of Dakar at nearly 40 villages.

Rain gauge at a village in Senegal

Once again this year during the middle of June the students went to the villages to install the rain gauges before the start of the wet season which begins in late June.  However, no rain had fallen at the end of June which seemed strange but not out of the norm.  Considering that the wet season only last for 3.5 months (June, July, August through mid september), it is critically important that any delay in rainfall only last for 1-2 weeks.

However, we are at the start of August, which is the wettest month of the year and only a negligible amount of rainfall has fallen at Dakar.

90 day accumulated rainfall at Dakar Senegal

Overall the amount of daily convection on any given evening has been smaller than normal over the Sahelian region.  For example tonight, there are only small areas of convection, which is not typical during this time of year.

EUMETSAT -Satellite Based Rain Rates over West Africa 8/4/14 at 12:30 AM GMT

Many of the weather systems - known as mesoscale convective systems (MCSs), such as the one that brought down flight 5017 (and linked to TS Bertha) are long-lived and travel across the continent.  They are organized by the African Easterly Jet at 10000 feet.    However, this year as these systems have moved towards Senegal, they have weakened and dissipated.   This is due in part to dry, stable air which has been over locations such as Dakar, Senegal since June.  The source of this air is the Sahara and even when large amounts of dust are not found in the atmosphere, the dry, stable air is still there.   We can find this stable air by looking at an atmospheric sounding which is released by balloon twice a day from Dakar, Senegal.

Sounding from 1200 UTC August 3, 2014 from Dakar Senegal

Somewhere between 1500 and 4000 feet, the relative humidity falls from 80 percent to less than 40% making cloud formation very unlikely in this from about 4000 to 15000 feet.   In addition, there is a stable lid near 4000 feet which stops clouds from growing vertically.   In todays sounding, there were also strong winds of 30 knots (35 MPH) which would disrupt clouds from  growing vertically.

It is my hope that this pattern will break soon, because not only is it going to impact farmers (and hence food security) in a major way this year, but also water resources and electricity (hydropower).   Large amounts of rainfall over the Guinea highlands provides river flow for the Senegal and Gambia River but also the large Niger river which is important to many countries.   The Sahelian drought of 1983 and 1984 continued through August creating life-threatening conditions and the migration of millions to urban centers.

During the next 4 weeks, African Easterly Waves (AEWs) are expected to become stronger potentially spawning tropical disturbances in the Eastern Atlantic.  However, it is unclear how many disturbances will form in the Eastern Atlantic with dry air still in place.   The tropical waves may have a much better chance over the Central or Western Atlantic for further development.  There is a AEW that should pass over Senegal in the next 72 hours and hopefully it will bring rain to Senegal.  

The impact of the oceans on the current and future climate of West Africa cannot be understated.  The warming of the Eastern and Central Pacific ocean temperatures have the potential to cause drought in West Africa. 

Sea Surface temperature anomalies 

Future warming of the World's oceans have the potential to create conditions similar to El Nino based on Global and Regional model projections in the mid to late 21st century.  The only way to reduce any possibility of harming future generations in West Africa is to limit global warming through reductions in greenhouse gases.  We need inter-generational policy.  President Obama has started the process.

UPDATE ON TS BERTHA 

Tropical Storm Bertha is now north of the Bahamas and still moving towards the northwest.  Most of the weather models are carrying Bertha to the east of the US and west of Bermuda.   However, there are some global models that are carrying it closer to the US as of this evening. The intensity of the TS Bertha is expected to increase, potentially becoming a minimum hurricane in a few days as the vertical wind shear begins to relax.  The latest satellite images show it becoming more organized.

Tropical Storm Bertha at 915 PM EST (August 3rd)

 If you live along coast, please monitor this storm over the next few days, especially as it relates to potential rip currents for the beach going crowd along the US East Coast.   This system has already been linked to the death of 118 in Burkina Faso ten days ago (http://gjenks-climatechangehu.blogspot.com/2014/07/storm-that-downed-air-algerie-5017-may.html), ---please be careful.