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The Intertropical Discontinuity/Intertropical Front
From the African Desk, Climate Prediction Center, NOAA
NOTE: The ITCZ for November-December is an experimental product.
December 1-10 2002 - The African ITCZ moved slightly south from its position during the previous period, and was located near 8.2 degrees north latitude. The western region (from 10W-10E) was located near 8.5N, while from 20-35E, the ITCZ was found close to 8.3N. Associated with the ITCZ, light rainfall continued to fall during December 1-10 along southern Liberia, Côte d'Ivoire, and Ghana, while precipitation increased substantially in parts of southwestern Ethiopia, eastern Kenya, and southern Somalia. Rainfall totals in these East Africa locations were regionally greater than 100 mm for the week. Increased rainfall activity was also noted in eastern Gabon, southern Congo, western DRC, and northwestern Angola.
November 21-30 2002 - The African ITCZ moved on average nearly one degree to the south from the previous ten day period. Previously located near 9.3 degrees north latitude, the current ITCZ was located closer to 8.3 degrees north. In the west (from 10W-10E), the mean position was near 8.8 degrees north, while from 20-35E the ITCZ was located near 8.1 degrees north. Rainfall remained light throughout most of the Gulf of Guinea countries, and little rainfall was estimated throughout southern Cameroon and CAR. Precipitation was also lighter than during the previous period in most of Kenya and Tanzania.
November 11-20 2002 - The Africa portion of the ITCZ moved around 0.7 degrees south from its position during the previous ten days. This placed the ITCZ near 9.5 degrees south latitude during the current period. From 10W-10E, the ITCZ was located near 9.9S, while from 20-35E the average location was closer to 9.0 degrees south latitude. This continued southward movement during the period was related to the decreasing rainfall trends seen along the Gulf of Guinea countries and further east into Ethiopia, Sudan, and Somalia. Rainfall increased, however, in parts of Gabon, Congo, and Angola.
November 1-10 2002 - The African ITCZ moved ~1.2 degrees southward from the final ten days of October. Although this southward movement was mearly half that of during the previous period, it was similar to much of the decending period since August. The overall average position during November 1-10 was 10.2 degrees north, while from 10W-10E, the average position was 10.6N, and 10.0N from 20-35E.
October 21-31 2002 - The ITCZ over Africa continued retreating to the south at a rapid pace of 2.1 degrees over the eleven day period. The convergence zone moved more rapidly southward during the current period than any period during the past three months. While the western region of the ITCZ had been progressing to the south at around a degree per period, the lastten days of October saw movement closer to two degrees south over the period. A similar situation was observed over the eastern Africa region (20-35E). The ITCZ in this region also jumped more than two degrees to the south from the previous period. The largest movement south from the previous period (~3 degrees) occurred near the 0 degree meridian. On the contrary, the least movement between periods was found in the region near Senegal/Mali. Examining the precipitation around the region, rainfall totals remained light around Côte d'Ivoire and north-central Ethiopia, while rains seem to be ending in Mali, Burkina Faso, and Niger. Rainfall remained heavy near southern CAR and north-central DRC.
October 11-20 2002 - The African region of the ITCZ continued moving southward at a similar rate to that of the previous two months and was located on average near 13.5 degrees north. While the current average position was 1.0 degrees south of the previous period, the climatoligical mean is 1.3 degrees south of the first ten days of October. Thus, due to the slower than normal southward movement during the current period, the ITCZ is now near it normal position. Both the western and eastern regions arewithin 0.3 degrees of their normal location. While the overall spread of rainfall diminished somewhat from the last analysis, heavy precipitation increased in some locations. Throughout much of CAR, extreme northern DRC, and near the Nigeria/Cameroon border, 10-day rainfall totals were significantly higher than during the first dekad of October. Areas receiving less rainfall include northern Nigeria, Burkina Faso, eastern Ethiopia, and central Somalia.
October 1-10 2002 - The Africa region of the ITCZ continued moving to the south at an average rate of around a degree every ten days. This follows a similar descent rate from that of the past five ten day periods and places the ITCZ on average near 14.5 degrees north latitude for the period. The western region of the ITCZ remains slightly further south than other areas, and was located near 15.3 degrees north latitude during the recent period. The eastern ITCZ region was located at a similar distance from normal, and was progressing southward at a similar rate as well. A feature that stands out is the continued lack of rain near central and southern Côte d'Ivoire. The area has received little to no rainfall since the normal start of the minor rainy season, although it appears that precipitation is increasing throughout the area. Regardless, dryness should persist after the rains end due to the very late start. It should also be noted that during the past ten days, rainfall decreased in southern Chad and northwestern Ethiopia, and increased around south-southeastern Sudan and eastern Ethiopia/central Somalia. Heavy rainfall in extreme southeastern Sudan helped to alleviate dryness throughout the area.
September 21-30 2002 - The African ITCZ continued moving south at a rate similar to the previous fifty days, and was located on average near 15.5 degrees north latitude. This location is around half a degree south of normal for the period and 0.6 degrees south from the September 11-20, 2002 average. The western region, from 10W-10E was located near 16.2N, compared to the 1979-2001 mean position near 16.7N. The eastern ITCZ region (20-35E) was located around 14.5N, or almost a degree south from last period. This period's average location was 0.3 degrees south of normal. Both ITCZ regions are moving southward at a similar rate to the climatological ITCZ. Rainfall weakened during the period, especially over the western Africa region. Sierra Leone did however receive heavier rainfall during the recent period. Rainfall was similar, if not lighter, throughout much of central Africa, though precipitation intensified in western Ethiopia and southern Somalia.
September 11-20 2002 - The African region of the ITCZ was located near 16.1 degrees north latitude, around a degree south from its previous average position. The current location is around three degrees south of its maximum northward extent which occurred during the first period of August. Since then, the ITCZ has progressed southward close to a quarter of a degree per period. The average 10-day location (~17.0N) is around 0.8 degrees south from the previous period. The eastern Africa region average position for the period is near 15.3N, or around half a degree south from last period. Although the current position near 15 degrees west longitude moved around two degrees south during the period, the remainder of the convergence zone progressed more steadily to the south. Rainfall decreased throughout much of western Africa, while other regions received comparable amounts. While Côte d'Ivoire saw continued dry conditions, Nigeria/Cameroon picked up locally heavy rainfall.
September 1-10 2002 - The ITCZ over the African region was located on average near 17.0 degrees north latitude, or around 0.8 degrees south of its position during the final ten days of August. The overall position remains south of the 1988-2001 normal (17.4N, or 0.9 degrees south from the previous period). When averaged over the entire April to August time period, the 2002 ITCZ was located south of normal in every five degree longitudinal increment except near the 35E meridian. The West African region of the ITCZ has continued steadily moving southward for the past 40 days, and remains around half a degree south of normal for the period. A similar situation exists for the eastern ITCZ region. Rainfall intensity decreased throughout the region and the northward extent of precipitation backed to the south. While most of Côte d'Ivoire remained dry, rainfall increased in much of southern Chad, north-northeast Ethiopia, and along the eastern Nigeria coast. Rainfall decreased from the previous period along coastal Guinea, southern Senegal, Sierra Leone, and western Ethiopia. >
August 21-31 2002 - The African region of the ITCZ continued moving southward, and was located on average near 17.8 degrees north latitude, compared to the climatologically normal position of 18.3 degrees north. Given the fact that the current location is almost one and a half degrees south of its maximum northward position that occurred during the first of August, it appears that this was indeed the peak position for the season. This period, the ITCZ location from 10W-10E (~18.6N) was located around 0.8 degrees south of normal. A low pressure region which moved westward from Burkina Faso during August 25-28 contributed to this southward bias, as strong winds from the north helped to push the ITCZ to the south. The eastern region of the ITCZ, was located around 0.3 degrees south of normal, or near 16.4 degrees north latitude. There was a fairly similar rainfall distribution compared to the second 10 days of August, though some areas differed. Although rainfall continued to fall heavily near the central Nigeria/Cameroon border, precipitation was lighter throughout much of southern Chad and northern Benin. Heavier rains did fall in parts of southwestern Senegal, west-northwestern Mali, and central Nigeria.
August 11-20 2002 - During this period, 2002, the ITCZ apparantly began its retreat southward, as the average ten day position was located around 0.7 degrees south from its previous position. The possibility continues to exist, however, that the convergence zone will again push northward before the end of the month. On average, the ITCZ was located around 0.3 degrees south of its 1988-2001 normal, but the western region (from 10 degrees west to 10 degrees east longitude) was located near normal. This region moved half a degree south from the first ten days of the month. The southward movement in the eastern region of the ITCZ (20-35 degrees east) was more dramatic, as it jumped almost a degree south from last period. The average location was near 17.2 degrees north, compared to a normal of 17.4 degrees north. Overall, a relatively zonal wind pattern kept the ITCZ fairly stable throughout the period, especially in the western portion of Africa. Compared to last period, rainfall increased in eastern Burkina Faso, southern and central Sudan, and throughout CAR, but fewer heavy rainfall episodes were noted in the region shown. Rainfall was lighter in Côte d'Ivoire, western Mali into northern Guinea, and extreme southeastern Sudan.
August 1-10 2002 - The African region of the ITCZ was located on average at 19.1 degrees north latitude, approximately 0.8 degrees north from the previous period and 0.7 degrees north of the climatologically normal position. From 10 degrees west to 10 degrees east, strong southerly winds have pushed this region of the ITCZ north of the 1979-2001 normal for the period. From 20-35 degrees east, this region is also north of its normal position, mainly due to the convergence zone location near the 35 degree east meridian which pushed almost two degrees north from the last ten days of July. The most outstanding feature this period is the increased rainfall in western Africa. Although much of Senegal, Guinea, Sierra Leone, and southern Mauritania received little precipitation during the last ten days of July, the first period of August brought much higher rainfall amounts to much of the region. Rainfall increased in Côte d'Ivoire as well, but decreased in eastern Mali, eastern Burkina Faso, along the Nigeria/Cameroon border, parts of central and southern Sudan, and in the highlands of Ethiopia. Though the Africa ITCZ normally reaches its northernmost point in the middle of August, the position during the first of the month is already further north than the normal peak.
July 21-31 2002 - The African region of the ITCZ was located on average at 18.31 degrees north latitude, compared with the climatologically normal position of 18.18 degrees north. This period's location is approximately 1.38 degrees north of its position during the last period when averaged over the entire 15W-35E domain. From 10 degrees west to 10 degrees east, the strong northward movement that occurred during the last period continued, as the average location for the end of July is actually further north than normal. This has not occurred for the region since mid-April this year. From 20-35 degrees west, the current average location is very close to normal for the period, and almost a degree north from last period. Overall for the year, this eastern region remains south of normal when compared to the 1988-2001 climatological mean. Even though the ITCZ moved nicely northward in extreme western Africa, rainfall in Senegal and neighboring areas diminished during the last part of July. Rainfall did increase, however, throughout much of southern and eastern Mali and southern Niger as well as in the Ethiopian Highlands, eastern CAR, and southern Liberia. Precipitation decreased in central Nigeria and further westward as the short dry season continued due to the northward progression of the ITCZ.
July 11-20 2002 - The African region of the Intertropical Convergence Zone lurched northward more than 1.5 degrees from its average position during the first ten days of the month. The average position of the ITCZ was near 17 degrees north latitude, compared to the climatologically-mean location 17.5 degrees north. The western convergence zone was located near its normal position, more than 1.5 degrees north from last period. This has helped to increase rainfall throughout much of southern Mali. After moving around 2.0 degrees northward during the recent ten days, the eastern area of the ITCZ was located near its 12-year normal position for the period. Areal coverage of rainfall increased in parts of western Ethiopia and southern Sudan as southerly winds pushed moisture into the area. Although heavy rains continued to fall throughout much of Nigeria, coastal Côte d'Ivoire and adjacent locations recorded only light precipitation, as seasonal dryness seems to have begun in the area. The jump northward in eastern Africa helped to bring heavier rains to parts of eastern Sudan which have been experiencing dryness.
July 1-10 2002 - The African region of the ITCZ was located on average at 15.4 degrees north latitude, around 0.2 degrees north from its average position during the last ten days of June. However, the mean climatological location of the convergence zone for the current period is near 16.6 degrees north. The satellite estimated rainfall for the period was less erratic with a further northward extent, when compared to the ITCZ mean image from the previous period. Both the western (10 degrees west to 10 degrees east) and the eastern (20-35 degrees east) regions of the ITCZ failed to progress northward with the pace of climatology. With slightly more than a month before the normal maximum northward extent, the overall seasonal position of the ITCZ remains much to the south of normal, expecially in the east.
June 21-30 2002 - The African portion of the ITCZ moved approximately 0.20 degrees northward from its average position during the previous 10 day period. The current average location of 15.18 degrees north is almost half a degree south of its climatologically normal position, although the western region is much closer than normal than further eastward. The location of the western ITCZ region is nearly as far away from the normal position as it was during the previous period. For the ITCZ from 20-35 degrees east longitude, stronger than normal northerly winds helped to push the convergence region south again for the second straight period. For the month of June on average, both western and eastern regions of the ITCZ were close to normal but slightly south. Rains increased in areas of southern Mali and Burkina Faso, but decreased in parts of Ghana, Côte d'Ivoire, and Liberia from the previous period.
June 11-20 2002 - This period saw the African region of the ITCZ located on average at 15 degrees north latitude, around half a degree northward from its position during the previous ten days. From 10 degrees west to 10 degrees east, the convergence zone moved slightly more than half a degree north from last period, while the eastern region (20-35 degrees east) was found nearly at the same average 10 day location. With the movement northward near the Atlantic coast, it is seen that Senegal received its first rains of the season as June 17 brought rains in excess of 100 mm throughout parts of the western coast. Rains also pushed further into the western areas of Mali, but the overall precipitation intensity for much of western Africa was not as great as from June 1-10. Further east, rains filled into the southeastern areas of Sudan, but as in western regions, the 10 day accumulated precipitation was not as great as previously throughout much of the east.
Jun 1-10 2002 - The African region of the Intertropical Convergence Zone was located on average at 14.6 degrees north latitude, approximately 1.5 degrees north of its position during the previous period. The ITCZ region from 10 degrees west to 10 degrees east longitude was located at 15.4N when averaged over the ten day period. This northward movement of around 1.3 degrees brought the region to within than half a degree of its climatologically normal position. The maximum northward extent this period occurred between the 0 and 5 degree west meridians, as relatively strong southerly winds pushed into the area. The eastern region of the Africa ITCZ (20-35 degrees E) continued its push northward that began during the previous period, as the mean location of this convergence region was located at 13.7N,almost 1.8 degrees north from the last period. A comparision between the current and previous mean graphics shows increased rainfall throughout virtually the entire Sahel region. A good example of this new convective activity is over the southern Chad area. Although little to no rainfall was evident during the last ten days of May, June brought with it widespread rains in excess of 25 mm for the period, with locally heavier amounts up to 150 mm.
May 21-31 2002 - The African portion of the Intertropical Convergence Zone was located on average at 13.1 degrees north latitude, approximately half a degree northward from its position the previous period. Although the ITCZ moved northward on average, the western region from 10 degrees west to 10 degrees east moved little and was located again at ~14.1 degrees north. From daily analyses, it was seen that the western ITCZ moved somewhat southward during the first half of the period, but began to march again to the north during May 26-31. From 20-35 degrees east longitude, the ITCZ raced northward more than two degrees during the last ten days of May. It can be seen from that this movement brought the eastern portion of the convergence zone closer to its climatologically normal position than at any time since the beginning of April, 2002. Again, the northward leading edge of rainfall corresponds well with the location of the ITCZ.
May 11-20 2002 - The African portion of the Intertropical Convergence Zone was located on average at 12.6 degrees north latitude, compared to the climatologically normal position of 13.6 degrees north. The western ITCZ region (from 10 degrees west to 10 degrees east) moved half a degree north from its position last week, and was located on average at 14.1 degrees north compared to a normal of 14.6 degrees north. As was the case during May 1-10, the eastern zone of the Africa ITCZ (20-35 degrees east) actually moved slightly south from its previous position. The eastern region of the ITCZ was located on average at 9.8 degrees north latitude, compared to the normal average position of 12.3 degrees north. Though the western region's position was near normal for the period, the ITCZ was decidedly south of normal from Niger eastward, with a maximum southward bias occurring near Chad. The cause for this southward position appeared to be a persistent high pressure area that was located over Libya during most of the period and the associated stronger than normal northerly winds preventing the convergence zone from pushing northward.
May 1-10 2002 - The African region of the Intertropical Convergence Zone continued moving northward from its position during the last ten days of April. After moving slightly to the south during the previous period, the convergence zone leapt forward approximately 1.3 degrees during the recent 10-day span with a final average latitude of 13.6 degrees north. There was increased rainfall in this western area, the northward leading edge corresonding nicely with the location of the tropical front. To the east (from 20-35 degrees east longitude), the ITCZ did move slightly northward, but remained much to the south of its climatologically mean position by almost two degrees latitude. A pattern similar to 2001 seems to be emerging this year, with rainfall slow to begin in areas of southern Sudan and Chad, as well as northern CAR, and eastern ITCZ position south of normal since April 1.
April 21-30 2002 - The African ITCZ remained fairly stationary in the west, but continued its northward progression in the eastern region. Compared to the previous period, the West African portion of the ITCZ (10 degrees W to 10 degrees E) actually moved slightly to the south when averaging over the entire 10 day period. During the last four days of the period, however, strong southerly flow resumed and began to move the convergence zone back to the north. As with the western region, the current ITCZ position in the east (from 20-35 degrees E) was located on average one degree south of climatologically normal. Unlike the west though, this region continued its steady northward movement during the final ten days of April. When comparing to the previous period, rainfall was seen to decrease in the area west of central Nigeria, and this corresponds well with the slight retrograding movement of the intertropical discontinuity.
April 11-20 2002 - The African ITCZ continued moving northward, on average located approximately one degree north from the previous period. The West African region of the ITCZ (10°W to 10°E) was again located just north of the 13 year average latitude, at 12.5 and 12.6 degrees north, respectively. The western region's ITCZ position was located near the normal position due to a southward bias from 10 to 0 degrees west longitude, and a northward bias from 0-10 degrees east longitude. The East African region of the ITCZ was again south of normal. Northerly winds in this region prevented the convergence zone from moving far enough north to approach the normal location, and in response, rains were lighter than normal in southern Sudan and northern CAR. Overall, the ten day accumulated rainfall distribution corresponded well with the average position of the ITCZ, as the northward leading edge of precipitation was located very near the convergence zone.
April 1-10 2002 - The West African portion of the ITCZ (10 degrees W to 10 degrees E) averaged near the long-term mean of 11.6 degrees N. In the east (20 to 35 degrees E, the ITCZ's average position of 8.0 N was 0.7 degrees south of its 1988-2000 mean. The ITCZ was north of the long-term mean across Burkina Faso and Nigeria and south of the mean over Guinea in the west and Sudan in the east. Consistent with this pattern, widespread showers fell to the south of the ITCZ from southern Guinea eastward to southern Sudan, with above-normal rains from southern Burkina Faso into Ghana, Togo, Benin, and parts of Côte d'Ivoire.
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