Dekad 1stto10th November, 2013
1.0 GENERAL METEOROLOGICAL 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.
1.1 SURFACE
1.1.1 Pressure Systems
- The Azores Highof 1026hPa strengthened by 2hPa compared to the previous dekad and by5hPa in relation to the climatological mean(1971-2000). It was located at 36ºN/27ºW over North Atlantic Ocean.
- St. Helena Highof 1025hPaweakened by 1hPacompared to the previous dekad and strengthenedby 7hPain relation to the climatological mean(1971-2000). It waslocated at 35°S/25°W over South Atlantic Ocean.
- Mascarene High of 1023hPastrengthened by1hPa compared to the previous dekad andremained stable in relation toclimatological mean(1971-2000). It was located at30°S/94°E over South Indian Ocean.
- The Thermal Low of1008hPa was located at 11°N/18°E over southern Chad. It remained stablecompared to the previous dekad.
Fig. 1a: Pressure Anomaly at MSL 1 to 10Nov2013
(source NOAA/NCEP) /
Fig. 1b: Pressure Anomaly at MSL1 to10Nov2013(source NOAA/NCEP)
1.1.2Inter-Tropical Discontinuity (ITD), Inter-Tropical Convergence Zone (ITCZ) and Congo Air Boundary (CAB)
Between the 3rddekad of October (blue line) and1stdekadof November(black line), 2013, the ITDmoved southward by 1 to4 degrees fromnorth Atlantic to southern Sudan. The CABremained quasi stationary over Uganda, Tanzania, DRC and Zambia. The ITCZ moved southward by more than 7 degrees over Kenya, Somalia and Indian Ocean (Figure 2).
Fig. 2: The mean position of ITD, CAB and ITCZ 1stdekad of Nov(black), 3rddekad of October2013 (blue)
The red and green triangles represent their maximum and minimum displacements respectively.
1.2 TROPOSPHERE
1.2.1 African Monsoon
At 925hPa level (figure 3a), weak to moderate intensity of the monsoon windswere observed over most parts of the Gulf of Guinea (GoG) countries. The intensity of the monsoon at 850hPa which prevailed over the GoG and most of central Africa countries was moderate. (figure 3b).
Fig. 3a: Mean wind at 925 hPa in m/s 1 to 10Nov
2013 (Source: NOAA/NCEP) /
Fig. 3b: Mean wind at 850 hPa in m/s 1 to 10 Nov 2013,
(Source: NOAA/NCEP)
1.2.4 Thermal Index (TI) Regime
During thefirst dekadofNovember, the Thermal Index (TI) regime at 300hPa in (figure 5a) had isothermvalue of 242°K over southernNigeria, Chad and Sudan, northern Cameroon and central Ethiopia and Somalia. Itextended overnorthern Angola, central Zambia and Malawi and southern Tanzania.The high TI regime ≥242°K provided prospects for heavy rainfall.
The analysis in figure 5b shows increased temperature anomalies of 0.5 to 2.5°K compared to normal (1971-2000) over the entire continent exceptover bordering area South Africawhere negative anomalies of 0.5 to 1°K were recorded.
Fig. 5a: TI at 300hPa (°k)1 to 10Nov 2013
(Source: NOAA/NCEP) /
Fig. 5b: TI Anomaly at 300hPa (°k) 1 to 10Nov 2013
(Source: NOAA/NCEP)
1.2.5 Relative Humidity (RH) at 850 hPa
The 850hPa level (figure 6a) had high RH value (≥60%) during thefirstdekad of NovemberoverGoG countries, Central and Eastern Africa countries,northern Angola and Zambia and Madagascar with peaks of 80% overGreat lakes countriesand central Ethiopia.The remaining northern and southernparts of the continent observed RH value ≤40%.
The RHanomalies for the firstdekad compared to the reference period 2002-2011 (figure 6b),werepositiveover most of the continent exceptover Morocco, Tunisia, southern Niger, Nigeria, Northern Cameroon and southern Chad including most of southern Africa countries.
Fig. 6a: RH (%) at 850hPa 1 to 10Nov 2013
(Source: NOAA/NCEP/ESRL: PSD) /
Fig. 6b: RH Anomaly at 850hPa1 to 10Nov 2013
(Source: NOAA/NCEP/ESRL: PSD)
1.2.6Relative Humidity (RH) at 700hPa
The1stdekad of Novemberhad highRH value ≥70% at 700hPa (figure 7a) over southern of GoGcountries, Central and Eastern Africacountries, Angola,Zambia, Malawi,northwestMozambiqueand Zimbabwe.
The parts with thresholdRH value ≥ 70% were veryfavorable fordeepconvectionthat generatedheavy rainfall as shown in figure 8.
The1st dekad of NovemberRH anomalies (figure 7b) weregreater than the reference period (2002-2011)oversome parts of continent includingmost of Algeria, Mauritania, Libya, Mali, Niger, greater part of Central Africa and East. Over the remaining part of Africa deficit values of RH were observed.
Fig. 7a: RH (%) at 700hPa 1to 10Nov2013
(Source: NOAA/NCEP/ESRL: PSD) /
Fig. 7b: RH Anomaly at 700hPa 1to 10Nov2013,
(Source: NOAA/NCEP/ESRL: PSD)
2.0Precipitation
Figures 8 indicate observed precipitation estimates in percentage of normal for the 1stdekad ofNovember.
2.1 Precipitation
Well above normal precipitation was observed over coastal Atlantic of GoG countries, Most of Ethiopia, Somalia, some parts of South Sudan, eastern CAR, border between Congo and DRC and bordering area of Zambia-Zimbabwe-Namibia. The heavy precipitationresultedfrom deep convection associated with high TI regime andRH ≥ 70%. However, below to well below normal precipitation was observed over central Cameroon, some parts of DRC and northern Zambia.
Details:
- North Africa: Observed generallynormal precipitation.
- The Sahel:Observed normal precipitation.
- Gulf of Guinea countries:Observed normal to well above normal precipitation.
- Central Africa countries: observed well abovenormal precipitationover western Gabon, border between Congo and DRC.
- GHA countries:observed well above normal precipitationover major part of the region.
- Southern Africa countries: Observed normal to well above normal precipitation.
Figure 8: Cumulative Precipitation in relation to the Reference in %1 to 10 Nov 2013
(Source: NOAA/NCEP)
3. Outlook valid for 15thto 28thNovember 2013
3.1 Precipitation
During the period 15th to 22ndNovember, 2013, high probabilityof moderate precipitation exceeding 75mm is very likely over extreme western Cameroon, greater parts of Gabon, some parts of Congo, central DRC andAngola, and some small parts of Uganda, Kenya and Ethiopia. From 23rdto 28th November, there will be persistence of moderate precipitation exceeding 75 mm overparts of Gabon, DRC, central Angola and Uganda. Otherwise, moderate precipitation is expected over Zambia and Madagascar.
- North Africa: Minimal precipitation amounts will be observed over this sub-region.
- The Sahel:Minimal precipitation amounts will be observed over this sub-region.
- Gulf of Guinea countries: Precipitation amounts ranging from 20mm to 75mm will be expected over southern part of the region.
- Central Africa countries: Precipitation amountsranging from 20mmto150 mm will be expectedover greater part of the sub-region.
- GHA countries:Likelyto observeprecipitation amounts ranging between 20mm and 150mm.
- Southern Africa countries:precipitation amounts ranging between 20 and 100mm arelikely to prevail over south-eastern part of this region.
Fig. 9a : Forecast of total precipitation(mm)
forecast15 to 22November2013
(Source: NCEP/GFS) /
Fig.9b : Probability forecast oftotal precipitation exceeding 75mm, forecast15 to 22November2013 (Source: NCEP/GFS) /
Fig.9b : Probability forecast of total precipitation exceeding 75mm, forecast23 to 28 November2013 (Source: NCEP/GFS)
3.2Temperature
Neutral to positive anomalies (Figure 10b) will be observed over most parts of theSahel, eastern Ethiopia, Kenya,Somalia, Tanzania, Zambia, Zimbabwe, northern Botswana, Namibia, Mozambique and Madagascar. Neutral to negative anomalies will be recordedoverremaining parts of the continent.
Fig. 10b: Temperature Anomaly forecast 15 to 22November2013,(Source: COLA)
3.3Soil Moisture
Fig 11b shows deficit in soil moisture over most parts of the continent except major part of Central Africa and somepartsofSouthern Africacountries where increase in soil moisture will be expected.
Fig. 11b: Soil moisture change 15 to 22 November 2013
(Source: COLA)
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