Climate Forecasts

CLIMATE FORECAST

The Climate Hazards Center (CHC) of the University of California Santa Barbara (https://www.chc.ucsb.edu/) provides GEOGLAM Crop Monitor with global and regional climate outlooks. These assessments are based on weather and seasonal climate forecasts from a variety of international and national sources. Regional climate outlooks in the CM4EW draw attention to abnormal rainfall and temperature conditions (observed and forecast) that may impact food production or pose other risks to society, with a focus on food insecure regions.

 

September 3rd, 2020
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For previous reports visit the Archive.

 

Climate Influences:

Movement towards a La Niña-like climate by the end of the year

The El Niño-Southern Oscillation (ENSO) is currently neutral and is expected to remain so through the northern hemisphere summer. By the end of the year (October – December), however, a transition to La Niña conditions is likely (~60% probability). La Niña conditions during October-December typically reduce rainfall in East Africa, Central Southwest Asia, southern Brazil, and central Argentina and increase rainfall in Southern Africa, Australia, and eastern Brazil.

 

Regional Outlooks:

East Africa
Above-average rainfall is expected to continue across much of the region through September

Rainfall since the start of the June-July-August-September (JJAS) long rains season has been average to above-average across much of the region. Average to above-average rainfall continued in August. In particular, torrential rains in mid-to-late August fell over Sudan, southeastern South Sudan, central and northern Ethiopia, and Uganda. Above-average rainfall throughout much of the JJAS season has resulted in flooding in numerous areas throughout the region, most recently in south Darfur, North and West Kordofan, Al Jazirah, Khartoum, Kassala, Blue Nile, the Red Sea States of Sudan, and southwestern and the Afar region of Ethiopia.

Both the 15-day and 1-month (Figure 1-middle) forecasts indicate above-average rainfall is expected throughout the northwestern parts of the region, particularly in northern D.R.C., South Sudan, southern Sudan, central and northwestern Ethiopia, and Eritrea. Figure 1-left indicates how the 15-day forecast would contribute to JJAS long rains seasonal totals, with average to significantly above-average rainfall recorded throughout the region. As the long rains season peaks and begins to tail into the October-November-December (OND) short rains season, we see a stark contrast in the anticipated rainfall (Figure 1-right). Seasonal forecasts from NMME and the Greater Horn of Africa 56th Climate Outlook Forum indicate the high likelihood of below-average OND rainfall across much of the region.

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Estimated and forecast percent-of-average anomaly since June 1st, a 30-day rainfall anomaly forecast, and a 3-month probabilistic rainfall forecast. The left panel is a UCSB Climate Hazards Center Early Estimate, which compares 2020 rainfall amounts to the 1981-2019 CHIRPS average. This figure indicates what the post-June 1st percent-of-average anomaly would be if the 15-day unbiased GEFS forecast from August 26th materializes.  The middle panel is a 30-day forecast from August 27th. The image shows the average of four Subseasonal Experiment (SubX) model forecasts from that day. The anomaly is based on the 1999 to 2016 model average. Skill assessments of SubX can be accessed here. The right panel is a 3-month NMME probabilistic forecast for October to December based on August conditions.

 

West Africa

Above-average rainfall expected through September across much of the Sahel

Late-July to late-August rainfall conditions have thus far retained many of the patterns observed in June and July: highly variable: average to above-average rainfall in the northern and eastern parts of the region and below-average rainfall along the Guinea Coast (Figure 1-left). Above-average rainfall in the northern and eastern parts of the region has provided generally favourable conditions for cropping and pastoral practices. However, saturated soils, coupled with several instances of torrential rains, have led to flooding in Niger, northern Nigeria, Mali, southwest Cameroon, and Chad. In contrast, limited and below-average precipitation since June has continued along the Gulf of Guinea, with seasonal rainfall totals less than 80% of the historical average in Cote d’Ivoire, southern Ghana, southern Togo, southern Benin, and southern Nigeria.

The 15-day forecast indicates above-average rainfall is expected in Senegal, northern Ghana, Mali, northern Burkina Faso, Niger, and southern Nigeria. In contrast, limited rainfall (<50 mm) is expected over the Guinea Coast countries, further increasing the June-to-present seasonal deficit (Figure 1-middle). The 30-day forecast (Figure 1-right) indicates above-average rainfall in the north, and average to below-average rainfall in the south is likely to continue through September.

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Estimated percent-of-average anomaly for July 26st to August 25th, estimated and forecast percent-of-average anomaly since June 1st, and a 30-day rainfall anomaly forecast. The left and middle panels are UCSB Climate Hazards Center Early Estimates. They compare 2020 rainfall amounts to the 1981-2019 CHIRPS average. The left panel shows the estimated percent-of-average anomaly from July 26st to August 25th. The middle panel indicates what the post-June 1st percent-of-average anomaly would be if the 15-day unbiased GEFS forecast from August 26th materializes. The right panel is a 30-day forecast from August 27th. The image shows the average of four Subseasonal Experiment (SubX) model forecasts from that day. The anomaly is based on the 1999 to 2016 model average. Skill assessments of SubX can be accessed here.

 

Southeast Asia

Likelihood of above-average rainfall to continue into September

Rainfall from late-July to late-August was average to above-average across much of the region, with monthly totals ranging from 120-200% of average in Myanmar, Thailand, northern Laos, northern Vietnam, Malaysia, Indonesia, and the Philippines (Figure 1-left). This increase in rainfall was particularly beneficial in the northern areas of the region where the wet season rainfall had been well-below-average since April. However, rains returned to below-average throughout the region in late August.

The 15-day forecast indicates below-average rainfall is expected to continue through the end of August, particularly in the north. Figure 1-middle indicates how the forecasted rainfall could contribute to increasingly below-average seasonal totals in Laos, central and southern Vietnam, and the northern Philippines (Figure 1-middle). Overall, the below-average rainfall forecast for August is unlikely to have a significant effect on rice growth. Meanwhile, dry season rainfall conditions have been favourable in the south. Lastly, the 3-month forecast indicates an increased likelihood of above-normal rainfall over much of the region from September to November (Figure 1-right).

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Estimated percent-of-average anomaly for July 26th to August 25th, estimated and forecast percent-of-average anomaly since April 1st, and a 3-month probability forecast. The left and middle panels are UCSB Climate Hazards Center Early Estimates. They compare 2020 rainfall amounts to the 1981-2019 CHIRPS average. The left panel shows the estimated percent-of-average anomaly from July 26th to August 25th. The middle panel indicates what the post-April 1st percent-of-average anomaly would be if the 15-day unbiased GEFS forecast from August 26th materializes. On the right is the 3-month NMME experimental probabilistic forecast for September to November 2020, based on August conditions. The forecast probability is calculated as the percentage of all 79 NMME ensemble members that fall in a given tercile (above/below/near normal).

 

Central America & Caribbean

Above-average rainfall expected to continue across the region in September

August rainfall has been average to above-average throughout the southwestern parts of the region, while rainfall in the northeast was below-average (Figure 1-left). Of note, positive rainfall anomalies exceeded 120% in Guatemala, Honduras, and southwestern and eastern Nicaragua and were less than 80% of the historical average in Costa Rica, Cuba, and Haiti. Heavy rainfall did occur in late-August over much of the western coastline of Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, and Panama.

The 15-day forecast indicates heavy, above-average rainfall is expected throughout the southwestern parts of the region, while conditions are expected to stay below-average in Cuba and Haiti. Given the above-average rainfall from the previous two weeks, this forecasted rainfall has raised some concern regarding the potential for flash floods and mudslides in the area, particularly in Guatemala, western Nicaragua, and Panama. Figure 1-middle indicates how this anticipated rainfall would impact the April-to-present rainfall totals which, overall, have been average to above-average. The 3-month forecast indicates an increased likelihood of above-normal rainfall across much of the isthmus, particularly in the southwest. The forecast is generally inconclusive (indicated by white) in Cuba and Haiti.

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Figure 1. Estimated percent-of-average anomaly for August 1st to 25th, estimated and forecast percent-of-average anomaly since April 1st, and a 3-month probability forecast. The left and middle panels are UCSB Climate Hazards Center Early Estimates. They compare 2020 rainfall amounts to the 1981-2019 CHIRPS average. The left panel shows the estimated percent-of-average anomaly from August 1st to August 25th. The middle panel indicates what the April-to-August percent-of-average anomaly would be if the 5-day unbiased GEFS forecast from August 26th materializes. On the right is the 3-month NMME experimental probabilistic forecast for September to November 2020, based on August conditions. The forecast probability is calculated as the percentage of all 79 NMME ensemble members that fall in a given tercile (above/below/near normal).

 

For previous forecasts and assessments, please see the report archive page.