African Centre of Meteorological Applications for Development Centre Africain pour les Applications de la Météorologie au Développement Ten Day Climate Watch Bulletin N 26 Dekad 11 th to 20 th September, 2015 HIGHLIGHTS Above to well above average precipitation was observed over southern Mauritania, Mali, Niger, Chad, Sudan, parts of Senegal, Guinea Conakry, eastern Sierra Leone, Burkina Faso, northern Benin, Nigeria, CAR and Ethiopia. However, below to well below average precipitation was observed over southern parts of Gulf of Guinea countries, northern Gabon and Equatorial Guinea, central Congo, parts of DRC and northern Angola. During the period 27 September to 03 October, 2015 rainfall ranging from 10 mm to 30 mm is very likely over northern Morocco, Algeria and Tunisia central southern Mali, northern Senegal and Senegal, southern Sudan, most of Ethiopia, Somalia, Kenya and South Sudan, northern Tanzania and central DRC. Rainfall ranging from 30mm to 50mm is likely over southern Senegal and Mali, northern Guinea, most of Côte d Ivoire, Ghana, Togo, Benin, Burkina Faso, Nigeria, Cameroon, Gabon and Congo, northern DRC, western Uganda and South Sudan. Greater than or equal to 50mm rainfall is likely over southern Guinea, most of Sierra Leone, the border between Nigeria and Chad, northern DRC and Ethiopia During the period 28 September to 10 October, 2015 rainfall ranging from 10 mm to 30 mm is very likely over northern Morocco, Algeria and Tunisia, southern Senegal, Mali, Burkina Faso, Chad and Sudan, eastern Côte d Ivoire, parts of Ghana, Togo and Benin, central Nigeria, most of South Sudan, Ethiopia, Uganda and Kenya, northern Tanzania,, central DRC, southern Congo and Gabon. Rainfall ranging from 30mm to 50mm is likely over Guinea, Sierra Leone, Liberia, central Ghana, Togo and Benin, southern Nigeria, most of Cameroon, CAR, Gabon and Congo, northern DRC and western Ethiopia. Greater than or equal to 50mm rainfall is likely over the border between Nigeria and Cameroon, most of Equatorial Guinea, bordering area of DRC-Congo-CAR and eastern DRC. 1
1.0 GENERAL CLIMATOLOGICAL SITUATION Subsection 1.1 provides the strengths of the surface pressure systems and ITD, CAB and ITCZ displacements while subsection 1.2 is on Troposphere and gives a brief on monsoon and relative humidity thresholds. 1.1 SURFACE 1.1.1 Pressure Systems The Azores High of 1023 hpa, strengthened its intensity by 2hPa compared to the previous dekad, and by 1hpa compared to climatological mean (1981-2010). It was located at 29 W/34 N in North Atlantic Ocean. St. Helena High of 1031 hpa, strengthened by 8hPa compared to the previous dekad and by 7hPa compared to climatological mean (1981 to 2010). It was at 1 W / 37 S in South Atlantic Ocean. Mascarene High of 1030hPa strengthened by 5hPa compared to the previous dekad and by 4 hpa compared to climatological mean (1981-2010). It was located at 89 E/32 S in Southwestern Indian Ocean. The Thermal Low had 2 cells of 1008hPa each at 1 W/18 N and 15 E/15 N over north of Mali and eastern Niger respectively. They remained stable compared to the previous dekad and climatological mean (1981-2010). Fig. 1a: Mean Pressure at MSL 11 th to 20 th September, 2015 (Source NOAA/NCEP) Fig. 1b: Anomaly of Mean Pressure at MSL 11 th to 20 th September, 2015 (Source NOAA/NCEP) 1.1.2 Inter-Tropical Discontinuity (ITD), Inter-Tropical Convergence Zone (ITCZ) and Congo Air Boundary (CAB) Between the first dekad (blue line) and 2 nd dekad(black line) of September, 2015 the ITD moved southward by 1 to 4 degrees over southern Mauritania, central Mali, Niger and Chad, It moved northward by 3 degrees over central Sudan. The CAB remained quasi stationary over Uganda, Tanzania with 3 degrees eastward displacement over southeastern DRC. The ITCZ was quasi stationary over Indian Ocean. Figure 2: The mean position of ITD, CAB and ITCZ 2 nd dekad (black), 1 st dekad (blue) of September, 2015 The red and green triangles represent their maximum and minimum displacements respectively. 2
1.2 TROPOSPHERE 1.2.1 African Monsoon At 850hPa level (Figure 3a), weak to moderate northerlies were observed over southern Libya, northern Niger, Chad and Sudan, while moderate easterlies dominated the southern African countries. The moderate to strong diffluent south easterlies prevailed over eastern Africa countries reducing prospects of rainfall. At 700 hpa (Fig.3b), moderate to strong easterlies were observed over the Sahel, central Africa and northern part of Greater Horn of Africa countries with the dominance of the strong cross equatorial flow. Weak moderate high Fig.3a: Mean wind at 850 hpa ( m/s) 11 th to 20 th September, 2015 (Source: NOAA/NCEP) Weak moderate high Fig.3b: Mean wind at 700 hpa (m/s) 11 th to 20 th September, 2015 (Source: NOAA/NCEP) 1.2.2 Dust loading particles Figure 4a shows a low load of dust particles (0.1 to 0.4g / m2) over North Africa, the Sahel, northern Gulf of Guinea countries, Ethiopia and Somalia. A moderate dust loading particles (0.4 to 0.8g /m2) was observed over southern Algeria, eastern Niger and western Chad. High dust loading of between 0.8 to 1.2 g / m2 was observed over western Chad. Fig. 4a: Dekadal Dust loading (g/m2) 11 th to 20 th September 2015 (Source: WMO SDS-WAS: BSC-DREAM8b) 3
1.2.3 Surface Dust Concentration Figure 4b shows a low concentration of dust 3 between 5 and 50μg/m over most of Algeria, Libya, Morocco, Egypt, Mauritania, Senegal, Mali, Burkina Faso, Nigeria, Chad, Sudan, South Sudan and Ethiopia, southern Niger, northern Côte d Ivoire, Ghana, Togo, Benin, Cameroon and CAR. A moderate concentration (50-200 μg/m 3 ) was observed over southern Morocco, southern Algeria, northern Egypt, Mauritania, Mali and Niger, central Chad and northern Somalia. A concentration of 200-500 μg/m 3 was observed over western Chad and northern Somalia. Fig. 4b : Dekadal Surface Dust Concentration (μg/m 3 ) 11 th to 20 th September 2015 (Source: WMO SDS-WAS: BSC-DREAM8b) 1.2.4 Wind at 200 hpa. During the second dekad of September, 2015 strong winds at 200 hpa were observed over northern part of the Sahel, Southern Africa, Equatorial region and northern sector latitude 20 N over North Africa, while light to moderate winds were observed over southern part of the Sahel, Central and Eastern Africa countries. Figure 3a: Mean wind at 200hPa in m/s 11 th to 20 th September 2015 (Source: NOAA/NCEP) 4
1.2.5 Relative Humidity (RH) at 850 hpa The 850hPa level (Figure 6a) had high RH value ( 60%) during the second dekad of September 2015, over southern part of the Sahel, Gulf of Guinea countries, Central Africa and Eastern Africa countries and Madagascar. Low RH values ( 40%) (Figure 6a), were recorded over North Africa, northern part of the Sahel and most of Southern Africa. The RH anomalies for the second dekad of September, 2015 compared to the reference period 2002-2011 (Figure 6b), were positive over most of the continent except over northern Algeria and Tunisia, parts of South Sudan, Ethiopia, Uganda, Kenya, Tanzania, DRC, Angola and Madagascar where negative anomalies of RH were observed. Fig. 6a: RH (%) at 850hPa 11 th to 20 th September 2015(SOURCE/.NOAA/.NCEP-NCAR/.CDAS1) Fig. 6b: RH Anomaly at 850hPa 11 th to 20 th September 2015 (SOURCE/.NOAA/.NCEP-NCAR/.CDAS-1) 1.2.6 Relative Humidity (RH) at 700hPa High RH values ( 60%) at 700 hpa (Figure 7a) were observed over the Gulf region of Guinea, the Sahel, Central Africa and most of Great Horn of Africa (GHA) countries. RH values 40% were observed over North Africa, northern sector of the Sahel and southern Africa countries. The RH anomalies for the second dekad of September 2015 compared to the reference period 2002-2011 (Figure 6b), were positive over most of the continent except over northern North Africa, Central Africa, Eastern Africa and some countries of Southern Africa where negative anomalies dominated. Fig. 7a: RH (%) at 700hPa 11 th to 20 th September 2015 (SOURCE/.NOAA/.NCEP-NCAR/.CDAS1) Fig. 7b: RH Anomaly at 700hPa 11 th to 20 th September 2015 (SOURCES/.NOAA/.NCEP-NCAR/.CDAS-1) 5
2.0 PRECIPITATION Figure 8 indicates observed precipitation estimates in percentage of normal for the 2 nd dekad of September, 2015. 2.1 Precipitation Above to well above average precipitation was observed over southern Mauritania, Mali, Niger, Chad, Sudan, parts of Senegal, Guinea Conakry, eastern Sierra Leone, Burkina Faso, northern Benin, Nigeria, CAR and Ethiopia. However, below to well below average precipitation was observed over southern parts of Gulf of Guinea countries, northern Gabon and Equatorial Guinea, central Congo, parts of DRC and northern Angola. Details: North Africa: Observed average precipitation. The Sahel: Observed above to well above average precipitation. Gulf of Guinea countries: Observed below to well below average precipitation. Central Africa countries: Observed below to well below average precipitation except over northerneastern Cameroon and parts of CAR where above average precipitation was observed. GHA countries: Observed average to above average precipitation except over central Ethiopia, northern Uganda and western South Sudan where below average precipitation was observed. Southern Africa countries: Observed average precipitation except over eastern coastal zone of South Africa where below to well below average precipitation was observed. Figure 8: Cumulative Precipitation in relation to the Reference in % 11 th to 20 th September, 2015 (Source: NOAA/.NCEP/.CPC/.FEWS/.Africa/.DAILY/.ARC 6
3. Outlook valid from 27 September to 10 October, 2015 3.1 PRECIPITATION During the period 27 September to 03 October, 2015, (Figure 10a) rainfall ranging from 10 mm to 30 mm is very likely over northern Morocco, Algeria and Tunisia central southern Mali, northern Senegal and Senegal, southern Sudan, most of Ethiopia, Somalia, Kenya and South Sudan, northern Tanzania and central DRC. Rainfall ranging from 30mm to 50mm is likely southern Senegal and Mali, northern Guinea, most of Côte d Ivoire, Ghana, Togo, Benin, Burkina Faso, Nigeria, Cameroon, Gabon and Congo, northern DRC, western Uganda and South Sudan. Greater than or equal to 50mm rainfall is likely over southern Guinea, most of Sierra Leone, the border between Nigeria and Chad, northern DRC and Ethiopia During the period 04 to 10 October, 2015, (Figure 10b) rainfall ranging from 10 mm to 30 mm is very likely over northern Morocco, Algeria and Tunisia, southern Senegal, Mali, Burkina Faso, Chad and Sudan, eastern Côte d Ivoire,, parts of Ghana, Togo and Benin, central Nigeria, most of South Sudan, Ethiopia, Uganda and Kenya, northern Tanzania,, central DRC, southern Congo and Gabon. Rainfall ranging from 30mm to 50mm is likely over Guinea, Sierra Leone, Liberia, central Ghana, Togo and Benin, southern Nigeria, most Cameroon, CAR, Gabon and Congo, northern DRC and western Ethiopia. Greater than or equal to 50mm rainfall is likely over the border between Nigeria and Cameroon, most of Equatorial Guinea, bordering area of DRC-Congo-CAR and eastern DRC. Fig10.a Precipitation forecast from 27 September to 03 October, 2015 Fig10.b Precipitation forecast from 04 to 10 October, 2015 (Source: ACMAD) (Source: ACMAD) 3.2 Temperature From 28 September to 06 October, 2015, neutral to positive anomalies (Figure 11), will be observed over the Sahel, most of central Africa, eastern Africa, North Africa and southern Africa countries including western Madagascar. However, Gulf of Guinea countries will be dominated by neutral to negative anomalies. Fig. 11: Temperature Anomaly forecast 28 September to 06 October, 2015 (Source: COLA 7
3.3 Soil Moisture The outlook of variation on soil moisture change (Figure 12), shows an increase in soil moisture over the Sahel, the Gulf of Guinea countries, north eastern Greater Horn of Africa (GHA) countries and parts of southern Africa countries. Figure 12: Soil moisture change 28 September to 06 October, 2015 (Source: COLA) 8