July 2021 Climate Forecast Discussion for Aug-Oct through Nov-Jan
Note: The IRI seasonal forecasts issued this month are based on the NCEP-CFSv2, CanSIPsv2, and COLA-RSMAS-CCSM4 models.
The SST forecast indicates that the tropical Pacific is currently ENSO-neutral and will likely remain so through the boreal summer. This small collection of models suggests a re-emergence of cool SST anomalies near the end of 2021 that meet the La Niña condition threshold of -0.5 C below average, and may potentially persist long enough to constitute a second La Niña event (5 consecutive overlapping seasons, according to NOAA’s conventions). The La Niña-like SST pattern predicted in the latter seasons of the forecast does impact the associated seasonal climate forecast. The SST forecasts over the upcoming seasons indicate warmer than normal SSTs in the equatorial Atlantic Ocean and the eastern tropical Indian Ocean that are likely to persist through the next couple seasons.
Precipitation forecasts show enhanced probabilities of above-normal precipitation over the Maritime Continent and much of eastern Australia particularly for the first three forecasted seasons. During Aug-Oct, enhanced probabilities of above-normal precipitation are also predicted across much of northern and eastern Europe; below-normal precipitation is more likely over southeastern South America, much of Chile, and along the east coast of tropical Africa – from southern Somalia to the northern half of Mozambique. The likelihood for drier conditions continues in Sep-Nov and Oct-Dec for both southeastern South America and Chile, and a likelihood for above-normal precipitation is forecast for much of Brazil. In the final forecast season, Nov-Jan, many of the above forecast patterns weaken, and chances for below-normal precipitation increase particularly over the southwestern United States and Mexico, and over much of eastern China and over Korea. Many, though not all, of these precipitation patterns are consistent with historical La Niña events, again pointing to the important of the SST predictions from these three models.
The first two seasons show an increased likelihood for above-normal temperatures for the high latitudes of the Northern Hemisphere, particularly over northern Asia. In Aug-Oct enhanced probabilities of below-normal temperatures are forecast for much of Alaska, except the northern coast, possibly in response to oceanic coastal waves bringing cold temperatures poleward from the 20-21 La Niña. By Oct-Dec, the forecasts favor below-normal temperatures across much of Canada and Greenland. Also, in Oct-Dec, an area of likely above-normal temperatures is forecast over the Rocky Mountain region of the United States, extended down to the US-Mexico border, and much of that signal remains in Nov-Jan.
