SUMMARY MAY 2013
Very well below normal precipitation (drought) prevailed over southern Angola and neighbouring area in Zambia. Precipitation for the month of May, 2013 shows above normal rainfall over parts of Benin and Togo, most parts of Nigeria, the extreme southern part of Chad, south eastern part of Ethiopia and over adjacent areas of Kenya and Somalia. Below normal rainfall were observed over Angola, Zambia, Malawi, Mozambique and Madagascar.
Otherwise, temperature increase of more than 2°C in relation to the reference period 1971-2000 prevailed over the Sahel and Sahara with peak of 3.5°C over southern Morocco and western Mauritania.
1. SYNOPTIC SITUATION FOR MAY 2013
This section shows the intensity of pressure centers, the circulation and its anomalies at 850hPa, the wind direction and speed in the middle and higher levels, thermal regimes at high level, relative humidity at 850hPa and 700 hPa levels, the Sea Surface Temperatures (SST) and the El Nino/Southern Oscillation (ENSO).
1.1 PRESSURE CENTRES:
Figure 1 below states the locations and status of the surface pressure systems:
· The Azores high of 1027hPa strengthened by 8hPa compared to the previous month and remained quasi- stationary in relation to the climatological mean (1971-2000). The centre was located at about 31ºW/43ºN over North Atlantic Ocean.
· St. Helena high of 1020hPa strengthened by 5hPa compared to the previous month and still strengthened by 1hPa in relation to the climatological mean (1971-2000). The centre was located at about 4ºW/30°S over South Atlantic Ocean.
· Mascarene high of 1022hPa remained as it was compared to the previous month, and was quasi- stationery in relation to the reference period 1971-2000. Its centre was located at about 82ºE/31ºS over southern Indian Ocean.
· The Thermal Low had three cells of 1009, 1008 and 1007hPa respectively. The first and second cell remained the same compared to the previous month while the third cell filled by 1hPa. Their centres were located at 2°E/15°N, 16ºE/14°N and 36ºE/19°N respectively over the African continent.
Figure 1a: Mean sea level pressure May 2013
(Source: NOAA/NCEP) /
Figure 1b: Mean Sea Level Pressure Anomaly May
2013 (Source: NOAA/NCEP)
1.2 WIND ANOMALIES (m/s) AT 850hPa
Figure 2 below shows the Wind anomalies at 850hPa level
The strong westerly wind anomalies with speed ranges between 4- 6m/s from central Algeria to Libya and also from Gabon through Congo to DRC. The remaining part of the continent experienced wind speed of ≤ 2m/s./
Figure 2: Wind anomalies (m/s) at 850 hPa May 2013
(Source: NOAA/NCEP)
1.2 THERMAL INDEX (TI) AT 300hPa
The TI regime at 300hPa level (figure 3a) for the month of March had isotherm value of 242°K over Senegal, Mali, northern Burkina Faso and Nigeria, Southern Niger, central Chad and Sudan and also Djibouti. In the southern part of the continent it extends over Angola and Zambia, Malawi, Mozambique and Madagascar. TI regime ≥242°K with high relative humidity (RH) ≥60% at 850hPa, triggered with heavy rainfall with floods and landslides over some parts. However, areas with TI value ≤ 241°K and low RH experienced rainfall deficits.
Figure (3b) shows positive anomalies between 0.5°K to 2.0°K over most of the continent except over south of Botswana, South Africa, a small part of Egypt and Sudan where negative anomalies ( 0 to -2°) were observed.
Figure 3a: Thermal Index at 300hPa May 2013 Figure 3b: TI Anomaly at 300 hPa May 2013
(Source: NOAA/NCEP) (Source: NOAA/NCEP)
1.3 RELATIVE HUMIDITY (RH) AT 850hPa
The high RH (≥60%) at 850hPa (figure 4a), was observed during the month of May, 2013 over most of central Africa countries, most of the Great Lake Regions, most of the GOG countries, over Ethiopia, Somalia and Madagascar. The RH values were less than the mean 2002-2011 over the GOG, the Sahel, most of central African countries, Ethiopia and South Sudan. RH values were greater than the mean (2002-2011) over the remaining parts of the continent (Figure 4b).
Figure 4a: Relative humidity at 850hPa May 2013 Figure 4b: Relative humidity anomaly at 850hPa May 2013
(Source: NOAA/NCEP) (Source: NOAA/NCEP)
1.4 Relative Humidity at 700hPa
The high RH values (≥60%) in figure 5a, were observed over most of central Africa countries, most of the GOG and the Great Horn of African countries, over Angola, Namibia and southern part Tanzania. The regions with RH ≥60% were very favorable for deep convection that generated heavy precipitation with high impact. The RH values in figure 5b were greater than the normal (2002-2011) over most of the continent except over Niger and CAR, parts Morocco, Algeria, Libya, Nigeria, Chad, Mali, Mauritania, Cameroon, North/ South Sudan, Ethiopia, Djibouti and Somalia where RH values were less than the normal (2002-2011).
Figure 5a: Relative humidity at 700hPa May 2013. Figure 5b: Relative humidity anomaly at 700hPa May 2013.
(Source: NOAA/NCEP) (Source: NOAA/NCEP)
1.5 SEA SURFACE TEMPERATURE (SST) AND EL NINO/SOUTHERN OSCILLATION (ENSO)
Neutral to warm conditions were observed over the central and eastern part of the Equatorial Pacific. Cool conditions were observed over western part of the Equatorial Pacific. Warm conditions persisted over Tropical North Atlantic Ocean. Neutral to warm conditions prevail over the Equatorial Atlantic of the Gulf Of Guinea and Tropical South Atlantic. The Mediterranean Sea observed warm to neutral conditions prevail over the Mediterranean Sea. Near neutral conditions prevail over much of central and western Equatorial Indian Ocean. Slight cooling initiated off the coast of The Greater Horn of Africa.
Figure 6: Sea Surface Temperature May 2013 (source: IRI)
2.0 CLIMATOLOGICAL SITUATION AND IMPACTS DURING MAY 2013
This section states the general climatological situation and its impact covering two major parameters, the temperature and precipitation.
2.1 PRECIPITATION
Figures (7a and b) indicate observed precipitation estimates in percentage of normal for May and March/ April/May, 2013 respectively.
2.1.1 MONTHLY PRECIPITATION
Precipitation for the month of May, 2013 shows above normal rainfall over parts of Benin and Togo, most parts of Nigeria, the extreme southern part of Chad, south eastern part of Ethiopia add adjacent areas of Kenya and Somalia. Below normal rainfall were observed over Angola, Zambia, Malawi, Mozambique and Madagascar. The remaining parts of Africa recorded normal precipitation.
2.1.2 SEASONAL PRECIPITATION
Seasonal precipitation for the months of March- April- May, 2013 (Figure 7b) showed above normal rainfall over Benin, Togo and Nigeria, the extreme southern part of Chad cutting into a small part of CAR and also over south eastern Ethiopia, northern Kenya and central Somalia. Below normal rainfall were observed over parts of Angola, Zambia, Malawi, Mozambique and eastern coast of Madagascar with well below normal rainfall recorded over southern Angola and adjacent parts of Zambia.
Figure 7a: Monthly Cumulative precipitation for May 2013(Source: NOAA/NCEP) / Figure 7b: Seasonal Precipitation for March- April- May 2013
(Source: NOAA/NCEP)
Figure 8: Surface temperature anomaly May
2013, (Source: NOAA/NCEP)
Figure 9: Surface temperature anomaly for March-April-May
2013, (Source: NOAA/NCEP) / 2.2 NEAR SURFACE AIR TEMPERATURE ANOMALIESThe highest positive temperatures anomalies (figure 8) ranging between 2°C to above 3.5°C prevail over southern Morocco, western Mauritania and Senegal, northern Libya and Egypt, north western border of Niger/ Nigeria and also central Namibia.
2.2 SURFACE AIR TEMPERATURE ANOMALY FOR MARCH-APRIL-MAY
High temperature anomalies for the months of March- April- May with values of 20C were observed over Senegal, Gambia and Guinea. High negative temperature anomalies of 1.50C were observed over western South Africa.
3.0 OUTLOOK
3.1 SEA SURFACE TEMPERATURE (SST) FORECAST
Forecast for SST anomalies of June-July-August (JJA) 2013.
· Pacific Ocean: Neutral to cool temperature conditions will be prevail over the eastern Equatorial Pacific and near neutral to warm temperatures will prevail over much of central and western Equatorial Pacific. Near neutral conditions are more likely over Enso region.· Atlantic Ocean: Warm conditions will persist over Tropical North Atlantic and near neutral conditions are expected over much of Equatorial and southern Atlantic Ocean.
· Indian Ocean and the Mozambique Channel: Near neutral conditions will prevail over Equatorial and south western Indian Ocean. / Figure 10: Forecasted Surface Ocean Temperatures for May 2013
(Source: IRI)
3.2 El Niño/La Niña
Figure 11 shows the forecast of dynamic and statistical models over Niño 3.4 (5°N–5°S, 120°W–170°W).In July 2013, majority of the dynamic and statistical models predicted near neutral Southern Oscillation (ENSO) situation for June-July-August, 2013. /
Figure 11: Ensemble multi model forecast
May 2013 (Source: IRI)
Figure 10 and 11 shows Predicted Sea Surface Temperature (SST) anomalies and the future characteristics of ENSO. The precipitation outlooks for the coming months are also provided.
3.3 PRECIPITATION OULOOK
Figure 12: Seasonal Precipitation Forecast for June- July- August,
2013 (Source: NOAA/NCEP)
3.3.1 PRECIPITATION OUTLOOK FOR JUNE- JULY- AUGUST
Below average precipitation is very likely over Equatorial Guinea, coastal parts Cote d’Ivoire, Ghana, Togo, Benin, Cameroon and Gabon and also over the eastern parts of Tanzania, Mozambique, Kenya and Madagascar. Near to above average precipitation is more likely in central and west part of Sahel region.
Figure 13: Seasonal Precipitation Forecast for July- August- September,
2013 (Source: NOAA/NCEP)
3.3.2 PRECIPITATION OUTLOOK FOR JUNE- JULY- AUGUST
Below average precipitation is very likely over coastal part Guinea Gulf, easternmost part of Sahel region, south of Sudan, north of south Sudan, coastal part of central Africa and many eastern Africa countries. Near to above average precipitation is more likely in central and west part of Sahel region.
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