SHORT-RANGE FORECAST FOR WEST AFRICA N° 0004

AFRICAN DESK, GFS MODEL (NOAA), UKMET and ECMWF: 08/22/2005

VALID 24, 48 and 72 Hours

I. CURRENT SITUATION (ANALYSIS) AT 0000UTC

- The MSLP analysis on the NOAA GFS, the UKMET, and ECMWF shows that the Azores’s High extends a ridge over the coastal areas of Morocco, Algeria and Tunisia. The St Helena High extends a ridge off the coast of Liberia and Cote d’Ivoire according to the Ukmet model, while the NCEP GFS and the ECMWF place the ridge to the south of the Equator. A band of low pressure system (1008hPa) occupies the Sahel region and southern Sahara, with a minimum over eastern Mauritania/northern Mali (1007hPa) /southern Algeria (1006hPa) according to GFS and ECMWF models, and extends over the northern Niger (1007hPa) according to Ukmet model.

- At 0000UTC, the ITD is located about 19 degrees North over the coast of Mauritania, rising to 23 degrees North N Mali/S Algeria, slopping to 20 degrees North over Niger, and 19 degrees North over Chad.

- The monsoon influx covers the central and eastern parts of the gulf of Guinean countries up to southern Sahel, and extends vertically to 925hPa.

- On the 925hPa analysis, the NCEP GFS model shows 4 vortices located respectively to SW Cape Verde, over central Mauritania, N Mali and north-eastern Niger. Those vortices extend vertically to 850hPa and overland by a ridge in the upper level. The same vortices are identified by the two others models.

- On the 850hPa analysis, all models show a vortex over Cote d’Ivoire/Ghana. GFS model shows another vortex over central Cameroon. ECMWF shows other vortices over Nigeria and W Sudan.

- On the 700hPa, easterly waves are well shown by GFS and Ukmet models.

- The satellite imagery at 1400UTC, August 22 2005 shows a very deep convection Senegal and Cape Verde, and over the Daffour. Mid level clouds are present over E CAR, central Cameroon, and SE Nigeria.

II. EVOLUTION (development) for T+24, 48, 72 Hours

- According to the 3 models, the Azores’s ridge will be maintained over the northern parts of Maghreb during the period. The southern Sahara and Sahel will be occupied by low pressure system (1010hPa) during the period. The St Helena ridge will intensify while extending northwards at T+48 and 72, to be over the coast of Liberia, Cote d’Ivoire and Ghana.

- The ITD will be quasi-stationary at T+24, and slightly shift northwards at T+48 and T+72 over Mauritania Algeria and Mali, while maintaining its position over Niger and Chad during the period.

- All models show that the vortex to the SW Cape Verde will rapidly move over the sea. The vortex over Mauritania will move westwards while filling up during the period. The vortex over Mali will move over Mauritania at T+48, and then fill up at T+72. The vortex over Niger will move NW over northern Mali at T+ 48, and then fill up there after according to GFS and UKMET. Another vortex will form over C Niger at T+72 according to ECMWF. The vortex over Cameroon will fill up at T+48. The vortex over W Sudan will move over W Chad/NE Niger at T+72.

- The monsoon influx will persist over the region the gulf of Guinean countries at T+48 and T+72

III. FORECAST

T + 24:

Ø Light rains are likely over SW Mali, Liberia, W Cote d’Ivoire, SW Burkina Faso, N Togo/Benin, Cameroon and CAR.

Ø Light to moderate thunderstorms and rains will occur over Guinea Bissau, Guinea Conakry, Gambia, S Senegal, SW Cameroon and Equatorial Guinea.

Ø Moderate to heavy thunder-activities are expected over Guinea Conakry, Guinea Bissau, and SE Chad.

T + 48:

Ø Light to moderate thunderstorms and rain over SE Mauritania, Sierra Leone, Liberia, N Ghana/Togo/Benin, SE Nigeria, Cameroon and Equatorial Guinea.

Ø Moderate to heavy thunder-activities are likely S Senegal, Gambia and Guinea Bissau.

T + 72:

Ø Light rain over Sierra Leone, N Cote d’Ivoire, S Chad and over CAR.

Ø Light to moderate thunderstorms over E Guinea Conakry, W Liberia, N Ghana/Togo/Benin, C Niger, N and W Cameroon.

Ø Moderate to heavy thunder-activities W Mali, E/S/W Burkina Faso, SW Niger, N Nigeria, SW Cameroon and Equatorial Guinea.

By: Augustin TCHOUANWO

NMS / ASECNA Cameroon

African Desk Training (NOAA)

Directed by: Wassila THIAW, Project Director, African Desk, USA