Global Precipitation & Temperature Outlook September 2021

3 September 2021

OVERVIEW
September 2021 will bring much hotter than normal temperatures to Southeast Asia and central and southeastern Brazil. The Colorado River Basin in the U.S. and much of the Brazilian Amazon can expect wetter than normal conditions.

PRECIPITATION OUTLOOK
Increased precipitation is forecast for the Colorado River Basin in the United States, including severe surplus anomalies - a return period of 10 to 20 years - in Utah and Arizona. Wetter than normal conditions of lesser intensity are expected in the remainder of the watershed and into the Northern Plains and Upper Midwest through Minnesota. Moderate surpluses are forecast from eastern Colorado into the Panhandles of Oklahoma and Texas, and in the Big Bend region and east of San Antonio.

Precipitation outlook. 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… — Precipitation outlook. 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.

On the East Coast, moderately wetter than normal conditions are forecast from New Jersey into Pennsylvania, Delaware, Maryland, and parts of the Virginias.

A few small pockets in central Nevada and Southern California will be moderately drier than normal. Moderate precipitation deficits are also expected in northeastern Alaska’s Yukon Flats.

In Canada, Newfoundland and Cape Breton Island in the east will be moderately wetter than usual.

Mexico’s outlook includes surpluses in a broad path from Sonora, where anomalies will be severe in the northeast, moderating through Chihuahua and the central states of Durango and Zacatecas, and intensifying as they reach into the Sierra Madre del Sur range. Anomalies will be extreme in central Michoacán and severe near Mexico City and Puebla.

Much drier than normal conditions will skirt the central Pacific Coast through Sinaloa, moderating across the Gulf of Mexico in Baja California Sur. Farther south, Acapulco can expect severe precipitation deficits while deficits near Mérida in the Yucatán will be moderate.

Moderate deficits are forecast in the Caribbean and in a few pockets of northern Central America. Some surpluses are expected on Nicaragua’s east coast.

In South America, much of the Brazilian Amazon will be wetter than normal with moderate to severe anomalies. Brazil’s small northeastern states can expect similar precipitation surpluses. Surpluses are expected in several regions across the northern arc of the continent from Quito, Ecuador through Colombia, the western and southern Orinoco Watershed in Venezuela and the Delta region, and pockets in the Guianas. Surpluses will be extreme to exceptional in the Meta River Basin spanning the border of Colombia and Venezuela. A pocket of moderate deficit is forecast near Caracas.

In Peru, moderate surpluses are forecast in Loreto Region in the northeast and in a pocket near Cusco in the south. Deficits will form paths through the Cordillera Occidental and Cordillera Oriental ranges. Central Bolivia will be drier than normal as will its eastern arm reaching into Brazil, and some pockets in Bolivia’s southwest. The bulk of central Chile will see precipitation deficits ranging from moderate to extreme, and deficits will reach well across the border into western Argentina. Argentina’s Chaco Region in the north can expect to be moderately wetter than normal with conditions reaching into Bolivia.

Europe can expect a few moderately drier than normal pockets in the Baltic nations, northern Poland, and the middle Dalälven River region of Sweden. Moderate surpluses are forecast for central Iceland, and moderate to severe surpluses for southern Russia near the Black Sea.

In Africa, wetter than normal conditions are forecast for Eritrea, northern Ethiopia, southern and eastern Sudan and east-central Chad. Surpluses will be intense in northern Eritrea and a pocket in southern Sudan. Uganda will be moderately wetter than normal overall with severe anomalies on the eastern border and into Kenya. Moderate precipitation surpluses are expected in northeastern Democratic Republic of the Congo.

Surpluses will skirt the northern coast of the Gulf of Guinea and will stretch across the breadth of central Cameroon. In West Africa, Senegal, Guinea-Bissau, and Guinea will be moderately drier than normal. Precipitation deficits are expected in pockets of nation’s on Africa’s Atlantic Coast from Gabon through Angola. In the Horn of Africa, pockets of deficit are expected in eastern Ethiopia, Somaliland, Somalia, and eastern Kenya. Anomalies will be extreme in central Kenya. Moderate deficits are forecast for southeastern Tanzania, Zimbabwe, central Mozambique, and southern Madagascar.

Precipitation anomalies in the Middle East include deficits on Turkey’s Black Sea Coast, moderate in the west but more intense in the east and near Georgia’s coast. The Caspian Coast in Azerbaijan will be moderately wetter than normal. A patchwork of precipitation anomalies is forecast for the southern Arabian Peninsula with pockets of surplus and of deficit. A pocket of South Khorasan, Iran will be drier than normal.

Moderate precipitation deficits are forecast in Russia’s Irkusk Oblast surrounding the Bratsk and Ust-Ilimsk Reservoirs on the Angara River. Some areas of moderate deficit are also expected in Primorsky Krai on the Sea of Japan and in the southern Kamchatka Peninsula. Few precipitation anomalies are expected in Central Asia.

India will be moderately wetter than normal in a broad path from southern Gujarat through eastern Rajasthan and into the northern Gangetic Plain. Precipitation deficits are expected in pockets of India’s Far Northeast and spanning the border of Uttar Pradesh and Bihar. Elsewhere in South Asia, pockets of Sri Lanka will be moderately wetter than normal reaching into Tamil Nadu, India; and, a patchwork of conditions is forecast in Afghanistan and Pakistan.

In East Asia, surpluses are forecast in central Honshu, Japan, moderate overall, while moderate deficits are forecast in northern Hokkaido. Mongolia will be somewhat wetter than normal in the eastern regions of the Hangayn and Altay Mountains and in the Mongolian Plateau. In China, surpluses are forecast in the Qinling Mountains of Shaanxi and Henan, large pockets of Inner Mongolia, and in Xinjiang around Urumqi and in the Kunlun Mountains. Northwestern Sichuan will be moderately drier than normal as will a few pockets of China’s Northeast in central Jilin and eastern Heilongjiang.

In Southeast Asia and the Pacific, northern Vietnam and Laos will be somewhat drier than normal as will Myanmar’s west coast and a pocket near Rangoon. Surpluses, primarily moderate, are forecast for central Myanmar surrounding Mandalay and in a pocket of the northwest. Pockets of moderate surplus are also forecast around Phnom Penh and Siem Reap, Cambodia, and along Vietnam’s southeast coast. Surpluses will be widespread in Malaysia, Indonesia, and Papua New Guinea with intense anomalies in the Lesser Sunda Islands. Moderate surpluses are expected in Mindanao, Philippines.

Precipitation in New Zealand will be nearly normal. Australia’s vast central Outback will be wetter than normal. Moderate precipitation deficits are forecast in pockets along the nation’s west coast from the North West Cape through the Blackwood River region in the south.

TEMPERATURE OUTLOOK
Temperatures throughout many regions of Southeast Asia and the Pacific will be much warmer than normal. Exceptional heat anomalies will be especially widespread in Myanmar, Thailand, Laos, Cambodia, the Philippines, and New Guinea.

Australia can expect warmer than normal temperatures across its northern half and throughout much of the southeast including Tasmania. While anomalies will not reach exceptional intensity - ranging from moderate to extreme - Top End in Northern Territory will be extremely warmer as will Brisbane and the Darling Downs region in Queensland. Severe warm anomalies will blanket Tasmania. New Zealand’s South Island will be extremely warmer than normal but less intense conditions are forecast for North Island. Temperatures in New Caledonia will be exceptionally warmer.

Temperature outlook. 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 t… — Temperature outlook. 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.

In East Asia, many regions of China will be warmer than normal with moderate anomalies overall punctuated by large pockets of greater intensity. Anomalies near the southern coast are expected to be severe to extreme, but exceptionally hotter temperatures are forecast for Taiwan. At the intersection of Sichuan, Yunnan, and Tibet (Xizang), warm anomalies will be extreme. On the Korean Peninsula, conditions will be moderately warmer than normal in the north with mild anomalies in the south. Southern Honshu, Japan can expect moderately warmer temperatures. Moderately warmer than normal temperatures will also prevail near Mongolia’s southern border in the central region of the Gobi Desert.

Though temperatures in much of India’s Gangetic Plain will be normal - along with a much cooler pocket on the border of Uttar Pradesh and Bihar near Nepal - most of the nation’s remaining extent can expect to be warmer than normal. Anomalies will be moderate overall in the bulk of central India but severe to exceptional in the states along the Bay of Bengal reaching into Telangana, and also in the southwest from southern Maharashtra into Karnataka. Warm anomalies in the Far Northeast will be severe to extreme. Elsewhere in South Asia, Bangladesh will be exceptionally hotter than normal and severe warm anomalies are expected in northwestern Nepal. Central and far northern Pakistan will be moderately warmer than normal but anomalies in the south will be intense. In Afghanistan, warm anomalies will be severe north of a line bisecting the country from Mazar-e Sharif past Kabul, and a pocket in Nimruz Province in the south.

In Central Asia and Russia, temperatures will be warmer than normal from, roughly, the Central Siberian Plateau through much of Sakha Republic to the Sea of Okhotsk, and on the Kamchatka Peninsula. Anomalies will be moderate overall but severe to extreme from southern Sakha Republic to the Sea of Okhotsk. Turkmenistan and eastern Uzbekistan are forecast to be moderately warmer than normal with similar conditions reaching into Kazakhstan’s southern extreme. Moderate warm anomalies are also expected south of Lake Balkhash in Kazakhstan. Tajikistan, too, will be moderately warmer in the west but anomalies in the east will be severe. Far eastern Kyrgyzstan will be somewhat cooler than normal while the country’s southern reaches will be moderately warmer.

Exceptionally hotter than normal temperatures are expected in the Middle East in much of Saudi Arabia, its smaller neighbors on the Persian Gulf, and west of the Euphrates River in Iraq. Warm anomalies will be nearly as intense in Yemen and severe in southern Oman. Most of Iran will be much hotter than normal with widespread exceptional anomalies in provinces on the Persian Gulf. Syria can expect moderate warm anomalies. Turkey’s Black Sea Coast will be cooler than normal reaching through coastal Georgia, and a pocket of warmer than normal temperature is forecast in eastern Turkey around Lake Van and in some pockets of the south.

While cooler than normal conditions are forecast in South Sudan, Southern Sudan, central Katanga in Democratic Republic of the Congo, and western Namibia, warm anomalies of varying intensity are forecast for many other regions of Africa. Across the north, anomalies will be moderate throughout Egypt, moderate to severe in Libya, and will reach exceptional intensity in several areas, including northeastern Sudan and pockets of Algeria, Mauritania, and Mali. Warm anomalies are forecast for nations along the Gulf of Guinea and reaching into some land-locked central African countries. On the opposite side of the continent in the Horn of Africa, heat anomalies ranging from moderate to exceptional are forecast for the Ethiopian Highlands and eastern Ethiopia, Somaliland, southern Somalia, and southern and far northern Kenya. Farther south, warm anomalies are expected in Tanzania, Mozambique, Zambia, Zimbabwe, Angola, northeastern Namibia, Botswana, northern South Africa, and Madagascar. Areas with a forecast of exceptional anomalies include Botswana, South Africa and southwestern Madagascar.

Much of Eastern Europe and the Balkans can expect relatively normal temperatures. Moderate to extreme heat anomalies are forecast for southern Norway, and some moderate anomalies are forecast in pockets of Sweden and Finland. Moderately warmer than normal temperatures are also forecast for Denmark and northern Germany, Scotland and Ireland, Switzerland, France’s southeastern quadrant and some pockets in the west, and Sicily. Anomalies in Corsica and Sardinia, however, will be more intense.

In South America, Brazil’s eastern two-thirds will be warmer than normal with exceptionally hotter temperatures dominating a vast expanse in the central and southeastern region of the country and some small states in the northeast. A moderately cooler than normal pocket is forecast near Manaus. Warm anomalies, primarily moderate, are expected in Ecuador, Colombia, and pockets of southern Venezuela and French Guiana. Moderately cooler than normal conditions are forecast in north-central Venezuela and the Orinoco Delta. In Peru, much of the Andes region will be warmer than normal and exceptional anomalies will be widespread in the central Peruvian Andes. Southwestern Bolivia will see warm anomalies, severe to extreme, reaching into Argentina and northern Chile. Heat anomalies in central Chile will be mild to moderate. Moderately warmer than normal temperatures are forecast in Paraguay, Uruguay, the Argentine Pampas and central Patagonia, and severe warm anomalies in La Rioja Province in western Argentina.

Though temperatures in Nicaragua will be relatively normal, most of the rest of Central America will be much warmer than normal. Moderate warm anomalies are forecast in the Caribbean.

Southern Mexico will be much warmer than normal between the Gulf of Mexico and the Gulf of Tehuantepec. Moderate to severe warm anomalies are forecast for the Yucatán. Mexican states on the central Pacific Coast will be warmer than normal as will a vast area in the nation’s central north from Chihuahua through Coahuila. In the northwest, however, conditions will be cooler than normal and will include extreme to exceptional cool anomalies in northeastern Sonora.

Cooler temperatures will reach into the United States Southwest. West of the Rockies, temperatures will be somewhat warmer than normal overall though anomalies will be severe in central California. Severe warm anomalies are also expected from northern Michigan into northern Wisconsin and throughout much of Peninsular Florida. The U.S. Northeast can expect moderate to severe warm anomalies. Most of Alaska will be moderately warmer than normal.

Temperatures in Canada’s Prairie Provinces will be relatively normal. Moderately warmer temperatures are forecast for parts of British Columbia, northern Quebec, and Newfoundland. Nova Scotia, however, will be extremely warmer than normal. In the Canadian territories, northern Nunavut will be moderately warmer as will several large pockets in the Northwest Territories.

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 2, 2021 which includes forecasts for September 2021 through May 2022 based on NOAA CFSv2 forecasts issued August 25 through August 31, 2021.

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.

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