Global Precipitation & Temperature Outlook for September 2017

5 September 2017

Overview
The September Outlook indicates much warmer than normal temperatures - conditions we'd expect to see once in 20 to 40 years - in many regions of the world including India's southern half, coastal West Africa, and the eastern Amazon Basin. Much drier than normal conditions are forecast for central India.

Precipitation Outlook
As seen in the precipitation map below, a large block of red in central India radiating outward and east in hues of orange and yellow indicates a prediction of drier than normal conditions ranging from moderate to extreme. Likewise, dry anomalies are expected in western India along a strip of Maharashtra's coast. Exceptionally dry conditions are forecast just north of Nepal in southernmost Tibet and in western Bhutan.

Mexico's west coast state of Sinaloa is expected to see severe to moderate dry conditions as will a block of central Mexico. Primarily moderate dry anomalies are expected in central South America including pockets in central Peru and across much of Bolivia into western Paraguay and Mato Grosso do Sul and Paraná, Brazil. However, conditions may be severe to extreme in central Bolivia and in small pockets of central Brazil.

A small pocket of exceptional dry anomalies is forecast for northeastern Ethiopia, and conditions in Hokkaido, Japan may be severe. Primarily moderate dry anomalies are expected in: southeastern Sudan, eastern Central African Republic, and southeastern Sumatra.

Wet anomalies ranging from moderate to exceptional are forecast for western China. Wet anomalies of lesser severity are forecast for: southern Cameroon, Uganda, southern Ethiopia, and scattered across East Africa; Tripura, India, Bangladesh, western Myanmar and northern India into central Pakistan; Turkmenistan and Tajikistan; the US southern Rocky Mountains and into Nevada; pockets of Colombia, Venezuela, northwest and far eastern Brazil; and central Western Australia.

Temperature Outlook
In North America, moderate to occasionally extreme warm anomalies are forecast for a vast expanse of central Canada reaching south into the western US, where temperatures may be exceptionally warmer in Southern California. Primarily moderate warm anomalies are expected in southern Florida but anomalies will reach south into Cuba where they may become extreme, as well as in Puerto Rico and Jamaica. Severe warm anomalies are expected in the northern Baja Peninsula; exceptional warm anomalies along Mexico’s central west coast; and moderate to extreme warm anomalies in much of Central America.

In South America, extreme to exceptional warm anomalies are forecast in the eastern Amazon Basin, French Guiana, and along the northern coast of Brazil’s far east. Primarily moderate warm anomalies are expected in the western Amazon region and in Colombia, Ecuador, and western and southern Venezuela, though anomalies may be more intense in a small pocket of southeastern Venezuela reaching into Guyana. Warm anomalies of varying intensity are forecast for much of Peru and are expected to be exceptional in a lengthy path in central Peru, which transitions to merely moderate in the south before increasing in severity again as it curves through western Bolivia into northern Chile and Argentina. Warm anomalies will also be intense in Uruguay and north into Rio Grande do Sul, Brazil.

Warm anomalies of varying severity are forecast for many parts of Africa but exceptionally warmer temperatures are expected around coastal West Africa, southern Somalia into eastern Ethiopia, across the Sahel, and northern Madagascar.

Severe to exceptional warm anomalies are forecast for much of the Arabian Peninsula and in Iraq west of the Euphrates.

India’s southern half is expected to be much warmer than normal with exceptional anomalies in the southeastern region and along the northern Bay of Bengal into Bangladesh. Extreme to exceptional warm anomalies are forecast for Southeast Asia - which may be especially intense in western Cambodia - and in Malaysia and Indonesia, particularly Sumatra.

In East Asia exceptional warm anomalies are forecast for Yunnan and Sichuan, China. Moderate to extreme warm anomalies are forecast for southeast China including Hainan, and also in Taiwan. Moderate to extreme anomalies are forecast across northern China, Mongolia, and across much of northern Russia.

Temperatures across much of Australia’s northern half will be warmer than normal and may be especially severe near Brisbane.

Only a few places are expected to be cooler than normal. Much cooler than normal temperatures are forecast in eastern South Sudan and in a small pocket of India just south of central Nepal. Northwestern Mexico will be somewhat cooler than normal.

Note on Administrative Boundaries
There are numerous regions around the world where country borders are contested. ISciences depicts country boundaries on these maps solely to provide some geographic context. The boundaries are nominal, not legal, descriptions of each entity. The use of these boundaries does not imply any judgement on the legal status of any territory, or any endorsement or acceptance of disputed boundaries on the part of ISciences or our data providers.

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 September 5, 2017 which includes forecasts for September 2017 through May 2018 based on NOAA CFSv2 forecasts issued August 25 through August 31, 2017.

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.