Extratropical Highlights –November 2023

 

1. Northern Hemisphere

The 500-hPa circulation during November featured above-average heights over the North Pacific Ocean, the western half of North America, Greenland, and most of Siberia, where a maxima in anomalies was recorded, and below-average heights over the Laptev Sea and Scandinavia (Fig. E9). The main land-surface temperature signals include above-average temperatures across most of North America, Europe, Asia, and Russia (Fig. E1). The main precipitation signals include below-average rainfall totals for the eastern half of North America and for regions along the west coast, and above-average rainfall totals for Europe and eastern Asia (Fig. E3).

 

a. North America

The 500-hPa circulation during November featured an amplified ridge over the western half of North America and below-average heights over the Hudson Bay and surrounding areas, with near-normal height anomalies elsewhere (Fig. E9).  Temperatures across Alaska, most of Canada, and the western half of the U.S. were recorded above-normal with all areas reaching at least the upper 70th percentile of occurrences (Fig. E1).  Precipitation totals were well below-average for most of the eastern half of Canada and the U.S., where anomalies were recorded in the lowest 10th percentile of occurrences (Figs. E3, E5, E6). Below-average rainfall was also observed across the Pacific Northwest (Fig. E3).

 

b. Europe and Asia

The 500-hPa circulation during November featured an amplified ridge stretching from off the east coast of Greenland to Siberia, with a maxima near the Yamal Peninsula in the Tundra of Siberia, and strongly below-average heights over Scandinavia with a minima located over Denmark and the Baltic Sea (Fig. E1).  Temperatures were moderately above-average for Europe and strongly above-average for Asia and Russia where countries such as Kazakhstan recorded temperatures in the highest 90th percentile of occurrences (Fig. E1).  Above-average rainfall was recorded across Europe and reached the highest 90th percentile of occurrences (Fig. E3).  Rainfall totals were also well above-average for Manchuria, China, and the Sikho Te-Alin Mountains of coastal Russia (Fig. E3).  The rest of Asia observed near-normal rainfall totals. 

 

c. Atlantic hurricane season

The 2023 Atlantic hurricane season produced 20 named storms, with seven becoming hurricanes and 3 of those becoming major hurricanes. The 2023 Accumulated Cyclone Energy (ACE) value was about 150% of the 1951-2020 median. Based on this activity, NOAA classifies the season as being above normal. An average season has 14 named storms, 7 hurricanes, and three major hurricanes.  Despite fewer than normal landfalling hurricanes, this hurricane season was the 4th busiest on record since 1950.  Other notable mentions include that the May outlooks fell within the observational range for Hurricane and Major Hurricane classifications.  However, the number of named storms and ACE were under forecast.  The August outlook did well to capture the observed number of named storms, hurricanes, major hurricanes, and ACE.

 

2. Southern Hemisphere

The 500-hPa height field during November featured a predominantly ridging pattern with 3 maxima located south of Australia, south of Africa, and the South Atlantic Ocean, and below-average heights over the Drake Passage (Fig. E15).  Temperatures were near-normal with the exception of above-average temperatures recorded in central and western South America, southern Africa and the Gulf of Guinea, and along the Great Dividing Range of Australia, as well as Western Australia, where some of these regions reached the highest 90th percentile of occurrences (Fig. E1).  Precipitation totals were well below normal for most of northern and central Brazil, as well as southern Africa, where totals were recorded in the lowest 10th percentile of occurrences (Figs. E3, E4). Along central Africa and a localized area of southern Brazil, rainfall totals were above-normal with some areas reaching the highest 90th percentile of occurrences (Figs. E3, E4).  The South African monsoon season runs from October to April. During November 2023, much of this area recorded below-average precipitation (Fig. E3), and area-averaged totals were in the lowest 10th percentile of occurrences (Fig. E4).

The Antarctic ozone hole typically develops during August and reaches peak size in September. The ozone hole then gradually decreases during October and November, and dissipates on average in early December (Fig. S8 top). During 2023, the ozone hole was predominantly above the 2012-2021 mean size and remained much larger than average thru November, The polar vortex has picked up speed during November and looks to be above-average at the start of December (Fig. S8 middle), while polar stratospheric cloud cover was below-average leading into November and largely absent (Fig. S8 bottom).