Data Void West Africa makes Tropical Cyclone Forecast for Cape Verde very Challenging

     Caption:  EUMUTSAT IR image of convection on Thursday 2000 EDT, 0000 UTC Friday

This evening a strong area of convection is found to the South of the Cabo Verde Islands and to the west of Senegal. This would make you think that there is no possibility of Cabo Verde being threatened by this storm right???  Wrong.   The GFS and WRF forecast shows that it is the area to the NE of the convective center that may develop into a strong tropical low. 

Unfortunately, the other global models (ECMWF and Candian models) show a very weak disturbance and not a clear indication that anything will happen this weekend.  So what is the big deal???

DATA...DATA..... or LACK OF DATA in Africa

Well, weather forecast models need good initial conditions in order to have a good forecast.   Well, that is just the real trick.  The atmosphere is three dimensional (x,y,z) and needs information about the initial state for models to have some degree of accuracy.  So every day, all around the world balloons are launched called radiosondes which provide information about the state of the atmosphere.

            Caption:  Radiosondes to provide information about the state of the atmosphere

The data from these balloons are fed into computer models all around the world and help them to produce accurate forecasts.  This is especially needed for severe weather such as tornadoes, severe thunderstorms, and hurricanes.  In fact, for hurricanes, the airforce and NOAA might fly inside of the hurricane use dropsondes which have parachutes rather than balloons to get a sense of what the atmospheric conditions inside of a hurricane.

However, in  West Africa, we do not have twice per day launches that occur to help models determine the state of the atmosphere. On a typical day, like today there are no measurements for potentially thousands of miles.  And most stations will only launch a balloon once per day.

    Caption:  Reported radiosonde launches for 20 August 2020.

This means that there is a poor representation of the state of the atmosphere at the time of the forecast.  Well, so what?  It means that if a tropical depression, storm or hurricane is forming off the coast of Africa the initial conditions could be poor leading to a poor forecast for coastal West Africa and Cabo Verde.  

At any rate, throughout the day the WRF model has provided some guidance about this weekend.   This is the WRF forecast from 0600 UTC 20 August.  

Caption:  WRF forecasted sea level pressure, wind and max reflectivity

If the WRF and GFS forecast are correct, then Friday, August 21 we will see the formation of an area of low pressure off the coast of Senegal.  This low will move to the NW and impact Cabo Verde starting Saturday night through Sunday.

If nothing happens, it gives a sense that we still have a long way to go in the forecasting realm.

Let's hope that that the weather system off the coast does not impact Cabo Verde in a big way.