Dry season brings and end to flooding season in Senegal but not without consequences.

Caption:  Daily Rainfall in Senegal over the last 30 days.  

This has been the first week when significant rains did not fall in Senegal. This is due to drier air from the Sahara that has been moving southward to signal the end of the rainy season (June-September) and start of the dry season (October-May).  What was unusual about this wet season was the abruptness and shifts from dry to wet conditions.     The rains began late with little or no rain falling in much of western Senegal during June and July.  Dry conditions still exist in Cabo Verde.

Caption:  Daily rainfall in Senegal over the last 90 days 

Then in mid-August, there was a poleward shift in the African Easterly Jet at 10000 feet and very wet conditions commenced with leading to flooding.  This was also the start of a very active tropical cyclone season tropical disturbances Dorian through Lorenzo. 

Caption: Satellite derived 30 day rain deficits (brown) or surplus (green) in mm

Satellite rainfall observations show that the 30 days of July 17-August 19 Senegal and Western Nigeria (circled in red) were very dry (left figure) but from August 19-17 September both regions were very wet.

What does it all mean??

Agriculture 

Farmers in this type of weather regime continue to take losses.  They cannot predict when to plant their seeds because the early rains are failing.   Even if they have planted and crops survive to the main rainy period (August) then floods finish off the process.   Because many cities have become urbanized, many people do not realize that these conditions promote food insecurity for rural residents but also for the country as a whole.  It also promotes reduced income because of losses in rural areas where many do not have access to currency.

Infrastructure Damage 

When flooding occurs it leads to property damages and losses of personal property that may not be insured.  It causes damage to roads, roofs and building structures. and slows down the supply chain for the movement of goods. These losses are likely underestimated in many parts of West Africa.  

Water Quality  and Quantity

Flooding can lead to contamination of groundwater and in urban areas the overrunning of sewers can further worsen the problem.  Large amounts of water are often sitting still for long periods of time because it cannot drain properly in urban areas and in other places will need to slowly evaporate.

Public Health:  Malaria and other Water Borne Diseases  

The sitting water caused by the heavy rains promote the breeding and spread of mosquitoes which may carry Malaria, Yellow Fever, and vector-borne diseases.    Malaria will peak in October or November on average and is likely to be influenced by the heavy rains in August and September of this year.  

The observed pattern of wetter conditions during the August and September which are linked to intense rainfall events are consistent with the published work using observations and models.  The impacts are at the personal level which included fatalities in Senegal this year.

It looks like the end has come but in another week-10 days, I will be nearly 100% confident that the rains have really stopped.  

As for tropical cyclones, the disturbances have now shifted towards the Guinea region.  Any systems that can impact the US or Caribbean will come from lower latitudes of West Africa.