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United States Department of Agriculture

Agricultural Research Service

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This section of the report will provide a rolling three month update on a monthly basis of the state of the climatic and ecological indicators used in monitoring areas at risk to RVF activity. These indicators include, global SST anomalies patterns, Equatorial Western Indian Ocean (WIO) and Eastern Pacific Ocean (EPO: NINO 3.4) SST anomalies, Southern Oscillation Index (SOI) and Outgoing Longwave Radiation (OLR) anomalies, Rainfall and anomalies, Normalized Difference Vegetation index anomalies and RVF risk map for Africa and the Arabian Peninsula.

June 2014

1. SOI and SST Indices

The SOI index slightly weakened in June with a value of 0.2 from 0.5 in June. These conditions generally reflect the prevalence of continued ENSO-neutral conditions across the eastern Pacific Ocean basin. June monthly SST anomalies in the NINO3.4 SST have remained steady at ~ 0.45°C and so are the WIO SST (0.3°C) anomalies indicating the prevalence of normal conditions over these ocean basins. Even though above-average sea surface temperatures (SST) (below) and in the NINO 1& 2 regions have increased and expanded over the eastern equatorial Pacific Ocean during June 2014, the absence of a clear atmospheric response to the positive SSTs indicates ENSO-neutral conditions, though the tropical Pacific continues to evolve toward El Niño. Nearly all model forecasts indicate the development warm ENSO 70% this summer (Niño 3.4 index: between 1.0°C and 1.4°C) and 80% in the fall. There are uncertainties to its evolution but projections are for at weak-to-moderate strength during the late fall and early winter with seasonal with Niño 3.4 SST values ranging between 0.5°C and 1.4°C.

The entire equatorial Pacific Ocean shows a pattern of above normal SSTs (+0.5°C to +2.0°C) except for the region from 30°S to 1°S with below-normal SSTs during the April 2014 to June 2014. Accordingly, the entire equatorial Indian Ocean between 30° N-S is now dominated by positive SST anomalies. Other regions of significant anomalies include the north Pacific Ocean, north Atlantic, equatorial Atlantic off the West African coast, the Pacific Ocean off the California coast, and south Indian Ocean off the southern Africa landmass which show significant positive and negative anomalies on the order of -/+1.0°C to -/+2.0°C. Outgoing Longwave Radiation (OLR) anomalies are used here as a proxy for tropical deep convection (rainfall). Reduced convection is shown in yellow to light brown and brown shades and increased/intense convection is shown by shades of blue. Some impacts from the current SST anomaly patterns can be observed in the pattern of global convective activity illustrated by the OLR departure patterns here. During the April 2014 to June 2014 period, drier-than-average conditions (>+35W/M2) are observed over the equatorial western Pacific Ocean between 120°E and 150°E, and enhanced cooler than average conditions (-40W/M2) to the immediate central Pacific indicating the propagating eastward shift of precipitation with warmer than normal SSTs. Convective activity continues to be prevalent over parts equatorial Africa particularly Sudan and parts of southern Africa, central Canada and Northern and Mid-US (-55W/M2), western central America and Southern Brazil. These patterns of depressed and enhanced convective activity coincide well with the patterns of SST departures. Monthly and weekly anomalies can be found here. Rainfall and associated anomalies (below) for Africa from April 2014 to June 2014 show rainfall concentrated from ~30°S to 15°N with a maxima along the equator. Areas of above normal rainfall (+50 to 250mm) include Gabon, South Sudan and equatorial West Africa.

Cumulative NDVI anomalies for Africa for April 2014 to June 2014 show positive anomalies concentrated over the South Sudan, western Ethiopia, Botswana, Namibia and northern South Africa following the above normal rainfall in these areas in the last several months. The RVF risk map below was derived from thresholding NDVI anomaly data to detect areas persistent of above normal NDVI. Periods of widespread and prolonged heavy rainfall lead to flooding of dambos and anomalous green up in vegetation, creating ideal ecological conditions for the emergence RVF vectors. For the period April 2014 to June 2014, the RVF persistence model identifies areas in Kenya, Botswana, central Namibia and Sudan and South Sudan where ecological conditions would support the emergence of RVF vectors. Enhanced surveillance is advised in these areas.

NDVI Anomaly RVF Potential

Last Modified: 7/11/2014
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