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The Intertropical Discontinuity/Intertropical Front
From the African Desk, Climate Prediction Center, NOAA
October 21-31 2001 - The ITCZ continued its rapid retreat southward. The West African portion of the ITCZ (10 degrees W to 10 degrees E) dropped 2.1 degrees latitude south to 11.4 degrees N, which was 1.3 degrees south of the long-term mean. This was the farthest south for October 21-31 since 1989 (11.2 N). In the east (20 to 35 degrees E), the ITCZ's average position of 10.3 N was 1.2 degrees south of last period's location and 1.1 degrees south of its 1988-2000 mean. The ITCZ was located well south of normal over much of its length, with only the far western end over Senegal and the far eastern end over Sudan near the long-term mean location. Consistent with this pattern, plentiful rains fell over western Ethiopia and extreme eastern Sudan, but dry conditions held sway across the rest of the region south to about the 6th parallel from around 25 E to 10 W.
October 11-20 2001 - The African ITCZ continued moving southward, but at a much faster than normal pace. The western region (10° west to 10° east) was located on average 2.7° south from the previous period, and 0.9° south of its climatological normal position. A southward bias remains for the eastern region of the ITCZ from 20-35° east, a pattern that has virtually existed for this entire season. This eastern region was located on average 2.1° south from the previous period, and 1.4° south of normal. A look at the 10-day satellite estimated rainfall map shows precipitation prominent throughout the CAR, and some amounts exceeding 50 mm for the period in northern Angola. This pattern coincides well with the southward movement of the ITCZ.
October 1-10 2001 - The West African portion of the ITCZ retreated 0.4 degrees latitude southward to 16.2 degrees N, which was 0.7 degrees north of the long-term mean. In the east, the ITCZ's average position of 13.6 N was 0.9 degrees south of last period's location and 0.5 degrees south of its 1988-2000 mean. The ITCZ was located south of normal over eastern Chad and western Sudan and slightly north of normal across Mauritania.
September 21-30 2001 - The western region of the African ITCZ retreated 0.9 degrees southward from its previous position. The eastern ITCZ region retreated approximately 0.7 degrees southward currently located on average at 14.5 degrees north latitude. Overall the ITCZ, averaged during the current period, was similar to earlier in the season, with the western region being mostly on track of its climatological normal, and the eastern region located south of normal. The latest 10-day satellite-estimated rainfall map gives a correspondence between rainfall location and ITCZ position, as rains have increased southward into coastal Gulf of Guinea and central African locations.
September 11-20 2001 - The West African portion of the ITCZ retreated 1.2 degrees latitude southward to 17.5 degrees N, which was near the long-term mean. Overall progress this season favored ample and timely rainfall for the Sahel countries. In the east, the ITCZ's average position of 15.2 N was near last period's location (15.1 N) and 0.5 degrees south of its 1988-2000 mean. The ITCZ positioned itself near its normal latitude over Mauritania and Mali, but south of normal from Niger to western Sudan.
September 1-10 2001 - The African ITCZ maintained similar spatial characteristics from the previous period, but continued a general southward movement. The average position of the western ITCZ region (from 10 degrees west to 10 degrees east longitude), was just south of its location during the final ten days of August. This position is reflected by the continued lack of rainfall in areas of Liberia and Côte D'Ivoire, with heavier rains extending from Senegal through northern Nigeria. The current eastern ITCZ position, averaged from 20-35 degrees east longitude, can be seen to have a southward bias from the climatologically mean position remains on the order of one degree, and the peak northward position did occur in mid- August. This feature is reflected in the cumulative satellite estimated rainfall map for the same period, with a lack of precipitation in areas of central Sudan. Overall, the average position of the African ITCZ is similar to the 1988-2000 mean, but a discrepancy does exist in eastern regions.
August 21-31 2001 - The region of the ITCZ from 10 degrees west to 10 degrees east continued its southward migration from the previous period. Although it appears that the peak northward position of the western ITCZ occurred a bit earlier than normal, the average position during the current period is almost co-located with the climatological mean, around 19 degrees north. This represents a southward movement of approximately 0.7 degrees from the previous period and 1.1 degrees south from the apparent northward peak, in the first week of August. A look at the ITCZ region from 20-35 degrees east shows a steep decline southward from its probable maximum northward position last period. Located on average at 16 degrees south, the eastern ITCZ is located about 0.8 degrees south of normal, as has been the trend this entire season. Overall, the average position of the African ITCZ remains south of the climatological mean, although recent precipitation totals have been similar to those expected during this time of year. As the ITCZ migrates southward in the upcoming weeks, it is likely that rainfall will increase in dryness-affected areas along the Gulf of Guinea.
August 11-20 2001 - The West African portion of the ITCZ retreated a small distance southward to 19.6 degrees N, which was north of the long-term mean of 19.3 N and 0.4 degrees south of its previous position (August 1-10, 2001). Overall progress so far this season has been fairly typical, except for the spike northward during August 1-10. The western ITCZ would have been near the 20th parallel again this period if not for strong northerly winds in the west during August 18-20 driving the humid air southward across Mauritania. In the east, the ITCZ jumped to its most northward position of the season, averaging 17.8 N from 20 to 35 degrees E longitude. This was 0.5 degrees north of the 1988-2000 mean and a significant advance of 1.4 degrees from the previous position. The ITCZ was somewhat south of its normal latitude over Mauritania, slightly north of normal from Mali to Niger, somewhat south of normal in eastern Chad and western Sudan, and north of normal over eastern Sudan. It should be noted that the confidence in the ITCZ's location over Chad and western Sudan was low due to lack of data in this area.
August 1-10 2001 - The African ITCZ resumed this years general pattern, with the western region located north of the climatological mean, and the eastern region located south of mean. The western region of the ITCZ (10 degrees west to 10 degrees east) was located on average at 20 degrees north, compared to the long-term mean position of 19.1 degrees. The ten day movement from last period of almost one degree north continued to influence diminishing rains along the Ivory Coast and increasing rainfall in Sahelian western Africa. The eastern region of the ITCZ (from 20-35 degrees east) did not see this trend in average movement, but actually moved about a half degree south of its position last period. Although this southward bias did not appear to affect rainfall in the region, this may be a hint that the ITCZ has reached its maximum northward position earlier than the 1988-2000 climatological figures indicate.
July 21-31 2001 - This period saw the average position of the African ITCZ move almost 1.5 degrees northward from the previous period, and it was located, on average, near 18 degrees north. A comparison between this period and the 1988-2000 climatological mean shows that the ITCZ is located about 0.3 degrees northward of the long term mean position. While the western region from 10 degrees west to 10 degrees east moved northward 1.1 degrees from its previous position, the eastern region from 20-35 degrees east moved almost 1.8 degrees north. This push northward of the eastern ITCZ region helped to increase rains in the areas around Chad and Sudan, improving the hydrometeorological situation substantially compared to previous periods.
July 11-20 2001 - The African region of the ITCZ moved on average 0.8 degrees north of its position during the previous period. Although the current location continues to correspond well with the climatological position, it remains south, overall, of normal. This southward bias can be seen most noticeably in the area from western Chad through eastern Sudan, where the convergence zone is located around 15.3 degrees north, compared to a twelve year mean position of 16.0 degrees north. Though a southward discrepancy exists, it is to a much lesser extent than earlier in the season, when monsoonal rains were much weaker in the region. As is normal for the period, the peak northward position of the ITCZ is occurring around 7.5 degrees west longitude. Partially due to this great northward position, seasonal rains have begun to diminish along coastal areas of the Gulf of Guinea.
July 1-10 2001 - The West African portion of the ITCZ remained stationary at 17.4 degrees N, which is close to the long-term mean of 17.5 N. Overall progress so far this season has been typical despite the failure of the ITCZ to advance northward during this period. In contrast, the ITCZ remained south of normal across eastern Africa (20-35 degrees E), its mean position of 14.2 N a full degree south of its long-term mean position. The convergence zone has been consistently south of normal during this season. The ITCZ was near its normal latitude from Mauritania east through Niger, but south of normal over Chad and Sudan. The result has been a tendency for above-normal temperatures, below normal humidity, and below-normal rainfall in the northern crop areas of Chad and Sudan.
June 21-30 2001 - This saw the African ITCZ move generally northward from its previous position in both the western and eastern regions. The western region (10 degrees west to 10 degrees east) is located north of its climatological mean due to rapid northward movement of about one degree latitude during the period. 10 day rainfall estimates show heavier rains in the area of eastern Mali, coinciding with this northern ITCZ position. The eastern Africa ITCZ from 20-35 degrees east is generally south of the long-term position. Again, the ten day rainfall estimate graphic shows a dip in precipitation intensity near the area of central Sudan. Overall, the African ITCZ appears to be basically on track with climatology, although a north/south bias in the western/eastern zone, respectively, remains apparent.
June 11-20 2001 - During this period, both the western and eastern regions of the African ITCZ moved closer to their climatological means. The average position of the western region ITCZ (from 10 degrees west to 10 degrees east) was located at 16.4 degrees north, exactly matching the normal position. From 20-35 degrees east, the average position of the ITCZ moved to 13.4 degrees north, compared to the 12-year mean position of 14.1 degrees. The entire African region of the ITCZ was located on average at 15 degrees north, while the climatological mean position was 15.3 degrees north. Rains continue to follow the general movement of the convergence zone as is indicated by slightly heavier rains in western Africa, short term dryness further east, and seasonal precipitation amounts elsewhere.
June 1-10 2001 - The African ITCZ remained generally south of its climatologically mean position, but rains did increase in the area surrounding northern CAR. The ITCZ between 20-35 degrees east remained nearly stationary from the previous period at an average latitude of 12.3 degrees north, putting it 1.3 degrees south of its long-term mean position. The western region (from 10 degrees west to 10 degrees east) moved slightly north on average from May 21-31, and was located 0.5 degrees south of mean. A look at the ITCZ mean graph shows the current and mean positions west of 0 degrees practically identical, but this is not the case for the sagging eastern region. Although it may seem that this season's movement of eastern and western ITCZ zones are dissimilar due to their relative positions, this is clearly not the case for the period since April 1.
May 21-31 2001 - During May 21-31, 2001, the African ITCZ moved northward from its position the previous ten days, but remained generally south of the climatological mean. The eastern region ITCZ was located more southerly from the long-term mean than in western Africa. The usual western (10 degrees west through 10 degrees east) and eastern (20-35 degrees east) regions are both the same distance south of their long-term means. Looking at the ITCZ from 10-30 degrees east, however, shows the current position much more south than any other region: 1.36 degrees south to be exact. This season's below normal rains through much of southern Chad, northern CAR, and southwestern Sudan continue to correspond well with this southward position of the ITCZ.
May 11-20 2001 - The West African portion of the ITCZ moved northward to 14.4 degrees N, which is close to the long-term mean of 14.6N. Overall progress so far this season has been typical. Eastern Africa (20-35 degrees E) saw the ITCZ jump northward to 11.9N, south of the long-term mean of 12.4N. The ITCZ in the east has tended to lag in its northward progress so far this season. The ITCZ was south of normal in the west near the Senegal-western Mali area, resulting in a somewhat slow start to the seasonal rains from southern Senegal southward to Guinea. In the east, the ITCZ was south of normal from eastern Chad to central Sudan. This is also consistent with estimated rainfall totals, which have depicted a slow start to the seasonal rains from southeastern Chad into south-central Sudan.
May 1-10 2001 - The ITCZ from 10 degrees west to 10 degrees east moved an average of 0.7 degrees north of its position from the previous period, while the average movement from 20-35 degrees east was 0.7 degrees south. The climatological mean position of the ITCZ moved north this period, but only the western region followed this trend. The eastern ITCZ was on average 1.6 degrees south of the 1988-2000 mean. Looking at the CPC rainfall estimate for May 1-10, the lack of precipitation in southern Sudan, Chad, and northern CAR reflects a more southerly position of the ITCZ and the associated vertical velocities that should normally accompany it.
April 21-30 2001 - The ITCZ west of 0 degrees moved south generally one degree from its previous position, while from 5 degrees east to 35 degrees east, the ITCZ moved just under 2 degrees north. Looking at the usual areas from 10 degrees west to 10 degrees east (western zone), and from 20 to 35 degrees east (eastern zone), the movement was 0.4 degrees north and 1.5 degrees north, respectively. Comparing current position to long-term mean, relative north-south positions of both the western and eastern zones were less than 0.1 degree from normal.
April 11-20 2001 - The West African region of the ITCZ movedsignificantly northward of the previous period, and was located on average 0.6 degrees latitude north of the long-term mean position. The mean position from 10 degrees W to 10 degrees E jumped to 13.0N, compared to 11.2N of the previous period. This coincided with heavier rains advancing inward toward areas of the western Sahel. Eastern Africa (20-35 degrees E) saw the ITCZ south of the long-term mean, averaging 1.4 degrees south of normal. There was little movement of the eastern part of the ITCZ from April 1-10. As the climatological mean moved northward, the gap from the current position grew larger. The ITCZ was generally north of normal from Senegal to Nigeria and south of normal from Chad to Sudan.
April 1-10 2001 - The ITCZ in West Africa (10 degrees W to 10 degrees E) did not advance significantly northward from it position on March 21-31, averaging 11.2 N this period versus 11.1 N during March 21-31. The April 1-10 position is slightly south of the long-term mean (1979-2000) position and considerably south of last year’s location (12.5 N). Over East Africa (20 to 35 degrees east longitude), the ITCZ advanced 1.1 degrees latitude north to 9.4 N. This is 0.5 degrees north of the 1988-2000 mean of 8.9 N. The ITCZ was south of normal from Chad to Mali, and this is a likely factor in the below-normal rains seen north of the Guinea coast this period.
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