The precipitation outlook for September 2015 indicates widespread areas around the world that may experience wetter conditions and widespread areas that may see much drier conditions. (For data sources see "About this blog post" below.)

Exceptional precipitation deficits are forecast for southern Mexico, Central America, northern South America, coastal West Africa, Indonesia, Malaysia, and Papua New Guinea. Severe precipitation deficits are forecast for central India.

Abnormal precipitation surpluses are expected in much of the continental United States from the Rocky Mountains eastward through the Central Plains states and the Midwest, and southward into Mexico’s northwestern states and Baja Peninsula. Greatest severity is forecast for the US Central Rockies. In South America, Argentina, central Chile, and Rio Grande do Sul, Brazil may experience abnormal to severe precipitation surpluses. Elsewhere, the following regions may be wetter than normal: Mediterranean Spain, northwest Africa (particularly Algeria), Uganda, northern Oman, Turkey, Syria, Turkmenistan, Tajikistan, and Western Australia.

Precipitation outlook for September 2015. Reds indicate below normal monthly total precipitation. Blues indicate above normal monthly total precipitation. The darker the color, the more extreme the anomaly relative to a 1950-2009 climatic baseline. … — Precipitation outlook for September 2015. Reds indicate below normal monthly total precipitation. Blues indicate above normal monthly total precipitation. The darker the color, the more extreme the anomaly relative to a 1950-2009 climatic baseline. Colors are based on the expected return period of the anomalies.

Predominately warmer than normal temperatures are expected in: the Southeast US, Southern California, Mexico's Baja and Yucatan Peninsulas, Central America, the Caribbean, much of South America, much of Africa, the Arabian Peninsula, Iran, India, Southeast Asia, China, Indonesia, and Malaysia.

Temperature outlook for September 2015. Reds indicate above normal monthly average temperature. Blues indicate below normal monthly average temperature. The darker the color, the more extreme the anomaly relative to a 1950-2009 climatic baselin… — Temperature outlook for September 2015. Reds indicate above normal monthly average temperature. Blues indicate below normal monthly average temperature. The darker the color, the more extreme the anomaly relative to a 1950-2009 climatic baseline. Colors are based on the expected return period of the anomalies.

About this blog post:

Each week, ISciences processes an ensemble of 28 seasonal temperature and precipitation forecasts issued by the National Oceanic and Atmospheric Administration's Climate Forecast System Version 2 (CFSv2). We present our results in a proprietary weekly report titled Global Water Monitor and Forecast: Precipitation and Temperature Outlook. This blog post summarizes our Outlook released August 24, 2015 which includes forecasts for September 2015 through May 2016 based on NOAA CFSv2 forecasts issued August 15 through August 21, 2015.

Technical details:

Each CFSv2 forecast is bias corrected by:
- Constructing probability density functions from CFSv2 hindcasts.
- Fitting the hindcast probability distribution functions to a generalized extreme value distribution.
- Using an inverse lookup to an extreme value distribution fitted to the observed temperature and precipitation record (Fan & van den Dool 2008, Chen et al. 2002).
The map colors depict the return period of the median forecast anomaly.
Regions where the interquartile range of the ensemble spans both above normal and below normal conditions are hashed as having uncertain direction.
Regions where the interquartile range of the ensemble divided by the median forecast is large (>0.4) are hashed as having uncertain magnitude.
Results are reported in terms of return period using a 1950-2009 baseline.