African Centre of Meteorological Applications for Development Centre Africain pour les Applications de la Météorologie au Développement Ten Day Climate Watch Bulletin N 15 Dekad 21 st to 31 st May, 2015 HIGHLIGHTS Above to well above average precipitation was observed over northwestern Côte d'ivoire, most of Guinea, Sierra Leone, Liberia, CAR and South Sudan, northern DRC and Ethiopia, southern Sudan and parts of Uganda. However Below to well below average precipitation was observed over southern Mali, Niger and Chad, most of Burkina Faso, Ghana, Togo, Benin and Nigeria, northern Cameroon, southern Gabon, Congo and DRC. During the period 3 to 9 June, 2015 moderate precipitation ranging between 10mm to 30mm is very likely over northern Morocco and Algeria, western Guinea, southern Mali, Burkina Faso and Chad, central Nigeria, northern Cameroon, the whole of CAR and Uganda, parts of Ethiopia, South Sudan and DRC. Precipitation ranging between 30mm to 50mm is likely over eastern Guinea, northern Côte d'ivoire, central Ghana, Togo, Benin and Nigeria, most of Congo and DRC. Precipitation above or equal to 75mm is likely over Liberia, southern Côte d'ivoire, Ghana, Togo, Benin, Nigeria and Cameroon, and most Gabon. During the period 10 to 19 June, 2015 moderate precipitation ranging between 10mm to 30mm is very likely over southern Senegal, Mali, Burkina Faso, Niger and Chad, most of Benin, Nigeria and DRC, northern Cameroon, the whole of CAR, parts of Congo, South Sudan, Kenya, Uganda and Ethiopia. Precipitation ranging between 30mm to 50mm is likely over eastern Guinea, northern Côte d'ivoire and Ghana, eastern Nigeria, central Cameroon and eastern Congo. Precipitation above or equal to 75mm is likely over most of Guinea, the whole of Sierra Leone and Liberia, southern Côte d'ivoire, Ghana, Nigeria and Cameroon, and most of Gabon. 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 1031hPa, strengthened by 5hPa compared to the previous dekad, and by 10 hpa in relation to climatological mean (1981-2010). It was located at 42 N/31 W over North Atlantic. St. Helena High of 1023 hpa weakend by 6hPa compared to the previous dekad, but strengthened by 2 hpa in relation to climatological mean (1981-2010). It was located at 26 S/19 E over South Atlantic Ocean. Mascarene High of 1028hPa weakened by 1hPa compared to the previous dekad, but strengthened by 8 hpa in relation to climatological mean. It was located at 36 S/92 E over South Indian Ocean. The Thermal Low of 1006hPa filled by 2hPa compared to the previous dekad. It was located at 13 N/16 E over southern Chad. Fig. 1a: Mean Pressure at MSL 21 to 31 May 2015 (Source NOAA/NCEP) Fig. 1b: Anomaly of Mean Pressure at MSL 21 to 3 May 2015 (Source NOAA/NCEP) 1.1.2 Inter-Tropical Discontinuity (ITD), Inter-Tropical Convergence Zone (ITCZ) and Congo Air Boundary (CAB) Between the 2 nd dekad (blue line) and 3 rd (black line) of May 2015, the ITD moved southward by 4 degrees over North Atlantic and northern Senegal, then moved northward by 1 degree over central Mali, southern Niger, southern Chad and Sudan. The CAB moved westward by 2 degrees over and eastern DRC, while the ITCZ moved northward by 1 to 4 degrees over Indian Ocean (Figure 2). Figure 2: The mean position of ITD, CAB and ITCZ 3 rd dekad (black),2 nd dekad (blue) of May 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), moderate north westerlies veering to north easterlies were observed over most of Egypt, northern Sudan and Chad, eastern Niger and northern Mauritania. The moderate to strong diffluent south easterlies over eastern Africa reduced prospects of rainfall. At 700 hpa level moderate to strong easterlies were observed over Gulf of Guinea, Central Africa and Eastern Africa (Figure 3b). Figure 3a: Mean wind at 850hPa in m/s 21 to 31 May 2015 (Source: NOAA/NCEP) Figure 3b: Mean wind at 700 hpa in m/s 21 to 31 May 2015,(Source: NOAA/NCEP) 1.2.2 Dust loading particles Figure 4a shows low dust loading ranging from 0.1 to 0.4g/m 2 over northern Morocco, Algeria and Tunisia, northeastern Libya, the whole of Egypt, northern Chad, most of CAR, Sudan and Ethiopia. High dust loading ranging between 0.4 to 1.2 g/m 2 was observed over parts of Chad and Algeria, southern Morocco, central Sudan and Gulf of Guinea countries. The highest dust loading ranging between 1.2 to 6.4 g/m 2 prevailed over southern Mauritania, most of Mali, Burkina Faso, Niger, northern Togo, Benin and Nigeria, and western Chad. Fig. 4a: Dekadal Dust loading (g/m2) 21 to 31 May 2015 (Source: WMO SDS-WAS: BSC-DREAM8b) 3
1.2.3 Surface Dust Concentration Figure 4b shows low surface dust concentrations ranging between (5 to 50µg/m 3 ) over northern Morocco, Algeria and Tunisia, most of Cameroon, CAR, Ethiopia and Somalia, and southern Sudan. Moderate concentrations (50 to 200µg/m 3 ) prevailed over southern Morocco, parts Algeria, most of Libya, Egypt, Sudan, Burkina Faso and Gulf of Guinea countries, southern Mauritania and Mali, and parts of Chad. The concentrations of 200 to 500 µg/ m 3 were observed over southern Algeria and Morocco, northern Mauritania, central Mali, northern Burkina Faso and Nigeria, most of Niger and western Chad. The highest concentrations of 500 to 2000 µg/ m 3 over south-eastern Niger and western Chad with peak of above 2000 µg/ m 3 over western Chad. Fig. 4b : Dekadal Surface Dust Concentration (μg/m 3 ) 21 to 31 May 2015 (Source: WMO SDS-WAS: BSC-DREAM8b) 1.2.4 Wind at 200 hpa. During the third dekad of May, strong winds at 200 hpa were observed over northern Sahel, North Africa and southern Africa countries. Over the rest of the continent, weak to moderate winds were observed Figure 3a: Mean wind at 200hPa in m/s 21 to 31 May 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 third dekad of May, 2015 over Gulf of Guinea countries, Central Africa, East Africa countries, northern Zambia, most of Mozambique and Madagascar. The RH value 40% were observed over the remaining parts of the continent. The RH anomalies for the third dekad of May, 2015 compared to the reference period 2002-2011 (Figure 6b), were positive over most of the continent except over southern Morocco, Mauritania, Mali, parts of Senegal, Guinea, Burkina Faso, Niger, Ethiopia, Angola, South Africa and Madagascar where negative anomalies of RH were recorded. Fig. 6a: RH (%) at 850hPa 21 to 31 May 2015(SOURCE/.NOAA/.NCEP-NCAR/.CDAS1) Fig. 6b: RH Anomaly at 850hPa 21 to 31 May 2015 (SOURCE/.NOAA/.NCEP-NCAR/.CDAS-1) 1.2.6 Relative Humidity (RH) at 700hPa The third dekad of May, 2015 had high RH value 70% at 700hPa (Figure 7a) over southern Mali and Chad, central Burkina Faso, Gulf of Guinea and Central Africa countries, Great Lakes Region, Malawi and Zambia. The RH value 40% were observed over the remaining part of the continent. The RH anomalies for the third dekad of May, 2015 compared to the reference period 2002-2011 (Figure 7b), were negative over most of the continent except over Sudan, northern Ethiopia and Somalia, Tanzania, Namibia and southern South Africa where positive anomalies of RH were recorded. Fig. 7a: RH (%) at 700hPa 21 to 31 May 2015 (SOURCE/.NOAA/.NCEP-NCAR/.CDAS1) Fig. 7b: RH Anomaly at 700hPa 21 to 31 May 2015 (SOURCES/.NOAA/.NCEP-NCAR/.CDAS-1) 5
2.0 PRECIPITATION Figure 8 indicates observed precipitation estimates in percentage of normal for the 3 rd dekad of May, 2015. 2.1 Precipitation Above to well above average precipitation was observed over northwestern Côte d'ivoire, most of Guinea, Sierra Leone, Liberia, CAR and South Sudan, northern DRC and Ethiopia, southern Sudan and parts of Uganda. However Below to well below average precipitation was observed over southern Mali, Niger and Chad, most of Burkina Faso, Ghana, Togo, Benin and Nigeria, northern Cameroon, southern Gabon, Congo and DRC. Details: North Africa: Observed near average precipitation. The Sahel: Observed near average precipitation except over most of Burkina Faso, southern Niger and Mali where well below average precipitation was observed. Gulf of Guinea countries: Observed below to well below average precipitation except over most of Guinea, Sierra Leone and Liberia, and northwestern Côte d'ivoire where well above average precipitation was observed. Central Africa countries: Observed near average to well above average precipitation except over southern Gabon, Congo and DRC where below average precipitation was observed. GHA countries: Observed near average to well above average precipitation. Southern Africa countries: Observed near average precipitation. Figure 8: Cumulative Precipitation in relation to the Reference in % 21 to 31 May 2015 (Source: NOAA/.NCEP/.CPC/.FEWS/.Africa/.DAILY/.ARC 6
3. Outlook valid for 3 to 16 June, 2015 3.1 Precipitation During the period 3 to 9 June, 2015 moderate precipitation ranging between 10mm to 30mm is very likely over northern Morocco and Algeria, western Guinea, southern Mali, Burkina Faso and Chad, central Nigeria, northern Cameroon, the whole of CAR and Uganda, parts of Ethiopia, South Sudan and DRC. Precipitation ranging between 30mm to 50mm is likely over eastern Guinea, northern Côte d'ivoire, central Ghana, Togo, Benin and Nigeria, most of Congo and DRC. Precipitation above or equal to 75mm is likely over Liberia, southern Côte d'ivoire, Ghana, Togo, Benin, Nigeria and Cameroon, and most Gabon. During the period 10 to 19 June, 2015 moderate precipitation ranging between 10mm to 30mm is very likely over southern Senegal, Mali, Burkina Faso, Niger and Chad, most of Benin, Nigeria and DRC, northern Cameroon, the whole of CAR, parts of Congo, South Sudan, Kenya, Uganda and Ethiopia. Precipitation ranging between 30mm to 50mm is likely over eastern Guinea, northern Côte d'ivoire and Ghana, eastern Nigeria, central Cameroon and eastern Congo. Precipitation above or equal to 75mm is likely over most of Guinea, the whole of Sierra Leone and Liberia, southern Côte d'ivoire, Ghana, Nigeria and Cameroon, and most of Gabon. Fig.8b : Probability forecast of total precipitation, 3 to 9 June, 2015 Fig.8b : Probability forecast of total precipitation, 10 to 16 June, 2015 3.2 Temperature Neutral to positive anomalies (Figure 9) will be observed over most of the Sahel, northern Gulf of Guinea countries, most of Chad, CAR, South Sudan and Sudan, parts of DRC and Kenya, northeastern Angola and parts of Zambia. Generally neutral to negative anomalies will be recorded over remaining parts of the continent. Fig. 9: Temperature Anomaly forecast 3 to 11 June, 2015 (Source: COLA) 7
3.3 Soil Moisture Figure 10 shows significant increase in soil moisture change over Gulf of Guinea countries, Burkina Faso, southern Mali and Niger, including central Africa countries over parts of Congo and CAR, northern DRC and South Africa. Figure 10: Soil moisture change 3 to 11 June, 2015 (Source: COLA) 8