Enlarge /. The global mean temperature for September was a new record.
September apparently did not feel like doing anything unusual, and so it was the warmest September ever in the world. This has been a trend this year with each month ending up in the top three. It has become increasingly clear that 2020 will likely be the second warmest year ever if it isn't the first.
Unlike in August, the neighboring US did not set a record in September, although it was still above the 20th century average. Again over the west coast a high pressure ridge dominated, which led to even more warm and dry weather for much of the western USA. But in mid-September a trough was built over the central United States to bring cooler air south.
Two other hurricanes – Sally and Beta – resulted in above-average rainfall in the southeast. The total precipitation for the adjacent US was slightly above average as a result, but the average, as usual, masks local differences. Drought conditions have widened and worsened in much of the west and there has been little relief to forest fire conditions.
Regarding these hurricanes, they have increased the number of named storms landing in the adjacent US to nine for the year. That was 1916 for most records, but the Hurricane Delta landing in Louisiana has since contributed to the staggering 2020 record.
In September, the number of catastrophes worth over $ 1 billion in the US rose to 16 in 2011 and 2017, for the most part since this (inflation-adjusted) measure began in 1980.
Some of the notable events in December.
Each of these disasters caused at least a billion dollars in damage.
September wasn't that warm for the eastern half of the US.
The total precipitation was almost average, but the regional differences are enormous.
Over 40% of the adjacent US is now in drought.
NOAA published its winter outlook on Thursday. This long-term outlook is based on a combination of observed trends, key slowly changing patterns, and model simulations. NOAA normally discusses the outlook for the next month and three months. However, this round includes the seasonal window from December to January to February.
If you got last month's update, this sounds pretty familiar. The biggest factor in the game is La Niña conditions in the Pacific, which are expected to last at least until spring. La Niñas tend to have a fairly defined impact on US winter weather, although the variability in weather does not go away. However, the cold surface temperatures in the Eastern Equatorial Pacific are generally promoting a shift in the US storm trail leading to more cold and wet weather in the north of the country and warmer and drier weather in the south.