African Centre of Meteorological Application for Development Centre Africain pour les Applications de la Météorologie au Développement Ten Day Climate Watch Bulletin N 27 Dekad 21 st to 30 th September, 2014 HIGHLIGHTS. 2.1 Precipitation Well above average precipitation was observed over southern Guinea, Sierra Leone, Mali, Burkina Faso, Cote d Ivoire, Ghana, Benin, and Sudan, central part of South Sudan, eastern Ethiopia, Uganda, DRC and northern Tanzania. However, well below average precipitation was observed over central Senegal, southern Mauritania, Ghana, Nigeria, Congo, and DRC. During the period 7 th to 14 th October 2014, high probability of moderate precipitation exceeding 75mm is very likely over southern Sierra Leone and Cameroon, eastern Gabon and Congo, and high lands of Ethiopia. From 15 th to 21 st October 2014, moderate precipitation exceeding 75mm is very likely to prevail over borders between Cote d'ivoire and Liberia, Nigeria and Cameroon, northern Gabon and eastern DRC.
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, thermal index (TI) regimes and relative humidity thresholds. 1.1 SURFACE 1.1.1 Pressure Systems The Azores High of 1031 hpa, strengthened by 9hPa compared to the previous dekad and by 10hpa in relation to the climatological mean (1971-2000).It was located at 42ºN/41ºW over North Atlantic Ocean. St. Helena High of 1021 hpa, weakened by 4hPa compared to the previous dekad and by 1hpa in relation to the climatological mean (1971-2000). It was located at 24 S/8 W over South Atlantic Ocean. Mascarene High of 1028hPa, strengthened by 4hpa compared to the previous dekad and by 2hPa in relation to the climatological means (1971-2000). It was located at 31 S/40 E over South Indian Ocean. The Thermal Low had two cells both of 1009hpa located respectively at 17 N/1 W and 14 N/17 W over northern Mali and southwest border between Niger and Chad. They deepened by 1hpa compared to the previous dekad. Fig. 1a: Mean Pressure at MSL 21 to 30 Sep 2014 (source NOAA/NCEP) Fig. 1b: Pressure Anomaly at MSL 21 to 30 Sep. 2014 (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 dekad (black line) of September 2014, the ITD moved southward by 2 to 5 degrees over central Mauritania, northern Mali, Niger and Chad, but remained quasi stationary over Sudan. The CAB moved eastward by 1 degree over Uganda, Rwanda and Burundi. The ITCZ remained quasi stationary over the Indian Ocean (Figure 2).
Figure. 2: The mean position of ITD, CAB and ITCZ 3 rd dekad of Sep (black), 2 nd dekad of Sep 2014 (blue) The red and green triangles represent their maximum and minimum displacements respectively 1.2 TROPOSPHERE 1.2.1 African Monsoon NOT AVIALABLE 1.2.2 Dust loading particles The map below (Figure 4a) shows low dust loading ranging from 0.1 to 0.4g/m 2 over North Africa, most parts of the Sahel and Sudan, northern GoG countries and Ethiopia, eastern Somalia and Djibouti. High dust loading ranging between 0.4 to 0.8 g/m 2 was observed over border between Mali and Algeria, southern Niger, northern Nigeria and eastern Chad. Fig. 4a: Dekadal Dust loading (g/m2) 21 to 30Sep 2014, (Source WMO SDS-WAS: BSC-DREAM8b) 1.2.3 Surface Dust Concentration Figure 4b shows low surface dust concentrations ranging between 5 to 50 µg/m 3 over northern parts of GoG countries, Morocco, the border between Algeria and Libya, southern Niger, north and south of Chad, northern Egypt, north and south of Sudan, southern Ethiopia and eastern Somalia. Moderate concentrations (50 to 200 µg/m 3 ) prevailed over the Sahel, most of Mauritania, Algeria and Libya, northern Mali, most of Niger, north of Chad, east of Egypt, Sudan, Ethiopia and Somalia, and Djibouti. The highest concentrations of 200 to 500 µg/ m 3 were observed over northern Mauritania, borders between Mali and Algeria, Niger, Chad and north of Libya Fig. 4b : Dekadal Surface Dust Concentration (μg/m 3 ) 21 to 30 Sep 2014, (Source WMO SDS-WAS: BSC- DREAM8b)
1.2.4 Thermal Index (TI) Regime During the third dekad of September, the Thermal Index (TI) regime at 300hPa in (figure 5a) had isotherm value of 242 K over southern Mauritania, central Mali, southern Niger extending over Sierra Leone, Cote d Ivoire, Ghana, northern Chad and Sudan, eastern Ethiopia and Somalia, southern parts of CAR, DRC, Cameroon and Gabon, central Angola, Zambia and Mozambique, northern Madagascar. The high TI regime 242 K covering tropical Africa provided prospects for heavy rainfall. The analysis in figure 5b shows increased positive temperature anomalies of 0.5 to 2.5 K compared to normal (1971-2000) over the entire continent except over northern Nigeria and South Africa, southern Namibia, Botswana and Madagascar where negative temperature anomalies of 0.5 K were observed. Fig. 5a: TI at 300hPa ( k) 21 to 30 Sep 2014 Fig. 5b: TI anomaly at 300hPa ( k) 21 to 30 Sep 2014 (Source: NOAA/NCEP) (Source: NOAA/NCEP) 1.2.5 Relative Humidity (RH) at 850 hpa The 850hPa level (Figure 6a) had high RH value ( 60%) during the third dekad of September over GOG countries, Central and Eastern Africa countries, and Madagascar. The RH value 40% were observed over the remaining parts of the continent. The RH anomalies for the third dekad of September compared to the reference period 2002-2011 (Figure 6b), were positive over most of the continent except over most North African countries, bordering area of Niger, Chad and Nigeria, south of Sudan, Ethiopia, Somalia, most of Kenya, Tanzania, southern DRC, northern Zambia, southern South Africa and northern Madagascar where negative anomalies of RH were recorded. Fig. 6a: RH (%) at 850hPa 21 to 30 Sep 2014 (Source: NOAA/NCEP/ESRL: PSD) Fig. 6b: RH Anomaly at 850hPa 21 to 30 Sep 2014 (Source: NOAA/NCEP/ESRL: PSD)
1.2.6 Relative Humidity (RH) at 700hPa The third dekad of September had high RH value 60% at 700hPa (Figure 7a) over Morocco, Algeria GoG countries, Central and Eastern African countries. The RH value 40% were observed over the remaining part of the continent. The parts with threshold RH value 60% were very favorable for deep convection that generated heavy rainfall as shown in figure 8. The RH anomalies for the third dekad of September compared to the reference period 2002-2011 (Figure 7b), were positive over most of the continent except over North African countries, Mauritania, Mali, most of Niger, eastern Chad, Sudan, most of Eretria, northern Ethiopia, southern Somalia, most of Kenya, northern Tanzania, southern DRC, Zambia, Malawi, Mozambique, southern South Africa and Madagascar where negative anomalies of RH were recorded. Fig. 7a: RH (%) at 700hPa 21 to 30 Sep 2014 (Source: NOAA/NCEP/ESRL: PSD) Fig. 7b: RH Anomaly at 700hPa 21 to 30 Sep 2014 (Source: NOAA/NCEP/ESRL: PSD) 2.0 PRECIPITATION Figure 8 indicates observed precipitation estimates in percentage of normal for the 3 rd September, 2014. dekad of 2.1 Precipitation Well above average precipitation was observed over southern Guinea, Sierra Leone, Mali, Burkina Faso, Cote d Ivoire, Ghana, Benin, Sudan, central part of South Sudan, eastern Ethiopia, Uganda, DRC and northern Tanzania. However, well below average precipitation was observed over central Senegal, southern Mauritania, Ghana, Nigeria, Congo, and DRC. Details: North Africa: Observed near average precipitation. The Sahel: Observed near average precipitation to above average precipitation. Gulf of Guinea countries: Observed near average to well below average precipitation. Central Africa countries: Observed near average to well above average precipitation. GHA countries: Observed near average to above average precipitation. Southern Africa countries: Observed near average precipitation.
Figure 8: Precipitation in percentage of average from 21 to 30 Sep 2014 (Source: NOAA/.NCEP/.CPC/.FEWS/.Africa/.DAILY/.ARC2)
3. Outlook valid for 7 th to 21 st October, 2014 3.1 Precipitation During the period 7 th to 14 th October 2014, high probability of moderate precipitation exceeding 75mm is very likely over southern Sierra Leone and Cameroon, eastern Gabon and Congo, and high lands of Ethiopia. From 15 th to 21 st October 2014, moderate precipitation exceeding 75mm is very likely to prevail over borders between Cote d'ivoire and Liberia, Nigeria and Cameroon, northern Gabon and eastern DRC. North Africa: Minimum precipitation amount is expected over north African countries The Sahel: Precipitation amounts ranging from 20mm to 75mm is expected over southern part of this sub-region. Gulf of Guinea countries: Precipitation amounts ranging from 50mm to 150mm is expected over most of the sub region. Central Africa countries: Precipitation amounts ranging from 50mm to 150mm is expected over the sub-region. GHA countries: Likely to observe precipitation amounts ranging between 50mm and 200mm. Southern Africa countries: Minimum precipitation amounts are expected over the region. Fig. 9a : Forecast of total precipitation(mm) Forecast 7 th to 14 th October 2014 (Source : NCEP/GFS) Fig.9b : Probability forecast of total precipitation exceeding 75mm, 7 th to 14 th October 2014(Source: NCEP/GFS) Fig.9b : Probability forecast of total precipitation exceeding 75mm, forecast 15 th to 21 st Oct 2014 (Source: NCEP/GFS)
3.2 Temperature Neutral to positive anomalies (Figure 10) will be observed over most part of the Sahel, DRC, Angola, parts of Ethiopia, Kenya, Somalia, Congo, Zambia, Botswana, Mozambique, Zimbabwe, Namibia, South Africa and southern part of Madagascar. Neutral to negative anomalies will be recorded over remaining parts of the continent. Fig. 10: Temperature Anomaly forecast 7 th to 15 th October, 2014, (Source: COLA) 3.3 Soil Moisture Figure 11 shows deficits in soil moisture change expected over most parts of the continent except over parts of GoG countries, CAR, DRC, Congo, Gabon, southern part of Angola, Ethiopia, eastern Somalia, southern parts of South Sudan and eastern South Africa where significant increase in soil moisture change will be expected. Figure 11: Soil moisture change 7 th to 15 th October, 2014 (Source: COLA)