bluewave

The seasonal forecast models continue to underestimate the mid-latitude 500mb ridging pattern leading to this persistent -PDO.

Yeah. But since there are so many missing days some years, it’s not an accurate annual average temperature. The average only includes the days with actual data. Lake Harmony only has snowfall starting with 2020-2021 and no temperatures. Data for October 1, 2020 through May 31, 2021 Click column heading to sort ascending, click again to sort descending. LAKE HARMONY 2.4 WNW CoCoRaHS 77.4 PORTLAND 2.7 WNW CoCoRaHS 63.8 PALMERTON 5.8 ENE CoCoRaHS 59.3 ALLENTOWN LEHIGH VALLEY INTERNATIONAL AIRPORT WBAN 58.1 MACUNGIE 1 SW COOP 57.1 SCHNECKSVILLE 2.7 SW CoCoRaHS 51.7 SCHNECKSVILLE 1.7 ENE CoCoRaHS 51.3 JIM THORPE 1.1 NNE CoCoRaHS 50.8 LEHIGHTON 1SSW COOP 49.2

Wettest September on record for ISP. This was the 3rd consecutive month with part of the area recording 10”+ of rain. So plenty of clouds and onshore flow kept the minimum temperatures up and the maximums down. 10 Wettest Time Series Summary for ISLIP-LI MACARTHUR AP, NY - Month of Sep Click column heading to sort ascending, click again to sort descending. 1 2026 8.76 2 2 1966 7.50 0 3 2008 7.46 0 4 2023 6.78 0 5 1975 6.57 0 6 1996 6.41 0 7 2004 6.37 0 8 1974 5.95 0 9 1999 5.65 0 10 1978 5.56 0 Monthly Data for September 2026 for Upton NY NWS CWA Click column heading to sort ascending, click again to sort descending. CT NORTHFORD 0.8 SW CoCoRaHS 12.33 NY CENTEREACH 1.3 NE CoCoRaHS 10.70 NY SELDEN 1.6 ESE CoCoRaHS 10.67 CT DARIEN 2.4 NW CoCoRaHS 10.35 NY PORT JEFFERSON STATION 0.3 SSW CoCoRaHS 10.27 NY RIDGE 1.8 SE CoCoRaHS 10.18 CT JEWETT CITY 3.0 ESE CoCoRaHS 9.98 NY RIDGE 1.5 SE CoCoRaHS 9.97 CT TRUMBULL 2.6 SSE CoCoRaHS 9.67 NY SETAUKET-EAST SETAUKET 0.7 SSW CoCoRaHS 9.52 CT DURHAM 1.2 W CoCoRaHS 9.48 NY MOUNT SINAI COOP 9.37 CT STAMFORD 1.0 S CoCoRaHS 9.35 NY RIVERHEAD RESEARCH FARM COOP 9.32 CT DARIEN 3.6 N CoCoRaHS 9.31 CT NORWALK 2.9 NNW CoCoRaHS 9.30 CT WALLINGFORD CENTER 1.9 WNW CoCoRaHS 9.30 CT NORWALK 1.4 ENE CoCoRaHS 9.15 NY SHIRLEY 2.9 N CoCoRaHS 9.15 CT NORWICH 2.5 NNE CoCoRaHS 9.14 CT CHESTER CENTER 2.7 WNW CoCoRaHS 9.11 NY ISLIP TERRACE 1.1 NNE CoCoRaHS 9.05 NY MANORVILLE 1.8 SSE CoCoRaHS 8.99 CT NORWICH 5.4 SE CoCoRaHS 8.95 CT LEDYARD 0.5 NE CoCoRaHS 8.85 NJ WAYNE TWP 2.3 ESE CoCoRaHS 8.76 NY ISLIP-LI MACARTHUR AP WBAN 8.76

September 2026 was the 3rd consecutive month with parts of the area going over 10” of rain. Monthly Data for September 2026 for Upton NY NWS CWA Click column heading to sort ascending, click again to sort descending. CT NORTHFORD 0.8 SW CoCoRaHS 12.33 NY CENTEREACH 1.3 NE CoCoRaHS 10.70 NY SELDEN 1.6 ESE CoCoRaHS 10.67 CT DARIEN 2.4 NW CoCoRaHS 10.35 NY PORT JEFFERSON STATION 0.3 SSW CoCoRaHS 10.27 NY RIDGE 1.8 SE CoCoRaHS 10.18

You can see a the continuous 500mb mid-latitude ridge from Japan across to the CONUS drove another big PDO drop in September. This has been a repeating theme during the 2020s. PDO attempts to go neutral than makes another big decline. The record warm subsurface east of Japan to south of the Aleutians tells the story.

One of the bigger beach erosion events of the 2020s so far.

The big story as we head into October is that the 500mb ridge is setting up further south than the recent seasonal models were forecasting. This has been the case each month going back to May and June. The October El Nino ridge is typically located over the EPO region of NW Canada and Alaska. The forecasts drop this ridge down into the CONUS at least for early October. We’ll need to see what happens mid to late month for a complete picture. So if this model error pattern continues into the winter and spring, then the typical Nino ridge north of the Great Lakes would adjust further south than previous super El Niño events. The December ridge can typically be further south anyway to some extent. So the big test will probably come JFM. It will be interesting to see how things work out. This stronger mid-latitude ridge axis since the late spring is causing the PDO to remain negative and the AMO positive. It’s also evident to the AAM disparity that you noted. New forecasts for early October Seasonal forecast from early September Typical October El Niño pattern

The actual SSTs late this fall into winter may continue to be near +30C in spots along the West Coast of Southern Mexico and Central America. During a much weaker El Niño in 2023-2024 they were at +29C. Plus the magnitude of the warmth in Nino 1-2 and 3 are forecast to pull the forcing east. This happened in 1997-1998 with much cooler SSTs.

The stratospheric interactions are also related to the actual tropical forcing in addition to the state of the QBO. During the later portion of the winter in 1983, it was more of a full-basin SST configuration compared to 1997-1998. All the guidance has a warm pool extending up along the West Coast of Mexico. This along with the record warmth in 1-2 and 3 lead to the forecast for split forcing leading to a strong eastward lean. During many recent seasons warm pools off the equator had had areas of forcing west of Mexico and to the east of Hawaii.

RONI is a relative metric to SST outside the actual ENSO regions. But the BOM RONI for Nino 1 and 2 are higher close to the actual ONI readings. So this is why we maintain the ONI alongside the RONI. Plus the agencies in South America use both since the record streak of temperatures there are related to the actual ONI readings. Remember Nino 1+2 has been one of the few ocean regions of the planet which didn’t warm prior to the 2023-2024 super El Niño. https://www.cpc.ncep.noaa.gov/data/indices/ 23SEP2026 25.4 4.7 28.8 3.9 29.7 3.1 29.8 1.1

The east based nature of 1982-1983 backed off during the winter relative to 1997-1998. The stratospheric conditions were related to the different nature of the ENSO forcing between both those seasons. The Central Pacific warm pool has already shifted the farthest to the east it has ever been. This is only expected to increase in the coming months.

Plenty of missing data before 2000 at MPO including no observations at all from the record 93-94 winter in NEPA. The column on the right is total number of missing days for each year. Notice how this recent period since 2000 is the most complete. But since there is no contract snowfall observer at MPO, we have to look to the surrounding areas volunteer snowfall observations. The older observations prior to the airport being build in the early 1960s may have been at a different altitude than the airport due to where the coop observers in the area lived. So some of the warm records could have been from a lower altitude. Time Series Summary for Mount Pocono Area, PA (ThreadEx) Missing Days right column Click column heading to sort ascending, click again to sort descending. 2025 46.4 0 2024 48.2 0 2023 48.3 0 2022 46.4 0 2021 47.5 0 2020 47.8 0 2019 46.2 0 2018 46.4 0 2017 46.8 0 2016 47.4 0 2015 47.2 0 2014 45.1 0 2013 46.6 0 2012 49.3 0 2011 48.3 0 2010 48.0 0 2009 46.3 0 2008 45.7 0 2007 46.5 0 2006 48.1 0 2005 46.5 0 2004 45.9 0 2003 44.8 0 2002 47.2 0 2001 46.2 0 2000 45.0 0 1999 46.9 9 1998 48.5 33 1997 45.0 22 1996 44.9 36 1995 52.1 232 1994 M 365 1993 46.9 128 1992 43.9 39 1991 46.5 46 1990 47.2 96 1989 42.9 67 1988 43.6 31 1987 44.2 27 1986 44.2 9 1985 32.3 242 1984 46.1 0 1983 46.6 1 1982 45.3 0 1981 45.4 0 1980 44.9 0 1979 45.8 0 1978 44.0 0 1977 45.4 1 1976 44.7 0 1975 46.4 0 1974 45.8 0 1973 47.4 0 1972 44.6 0 1971 45.4 0 1970 44.9 0 1969 44.9 0 1968 45.1 0 1967 44.6 0 1966 44.3 0 1965 44.5 0 1964 45.9 0 1963 44.4 0 1962 44.4 0 1961 27.5 331 1960 46.9 137 1959 37.3 216 1958 44.2 4 1957 46.9 7 1956 45.6 3 1955 47.1 7 1954 47.0 4 1953 48.2 20 1952 47.1 0 1951 46.6 0 1950 45.8 1 1949 53.4 182 1948 47.1 92 1947 44.8 0 1946 46.5 0 1945 45.2 0 1944 45.1 0 1943 44.3 0 1942 45.6 0 1941 44.4 0 1940 41.7 0 1939 44.5 0 1938 46.0 0 1937 44.8 0 1936 44.6 0 1935 43.9 0 1934 43.3 18 1933 46.6 78 1932 42.5 0 1931 46.8 0 1930 44.6 56 1929 45.5 0 1928 48.5 61 1927 48.8 84 1926 51.3 204 1925 60.1 243 1924 43.2 151 1923 49.8 212 1922 51.4 181 1921 46.4 122 1920 43.2 0 1919 45.7 0 1918 45.3 0 1917 42.2 0 1916 44.0 0 1915 50.8 90 1914 44.6 122 1913 38.5 143 1912 43.9 0 1911 46.3 5 1910 45.0 3 1909 45.4 9 1908 44.7 11 1907 41.9 5 1906 45.3 1 1905 44.7 0 1904 41.9 1 1903 44.0 12 1902 44.7 4

The current forecasts have it more east based mid-season than 1982-1983. That one was more full basin than 1997-1998 during the winter. With it becoming most east based late spring into early summer 1983. Which was part of the reason that February 1983 was better than 1998.

Even though the CFS forecast was too weak with the current all-time daily +5 Nino 1+2, it has a 2nd peak late next spring into the early summer. These very long range forecasts aren’t as accurate. But even the Euro extended is showing something similar. 1982-1983 had a second Nino 1+2 peak in June 1983 which was stronger than the one from the fall. But this fall is so much stronger than 1982 that the models have a lower peak late next spring. The 1983-1984 La Niña was significantly weaker than 1998-1999 since it got off to such a late start with a much weaker cold pool. We’ll get a new update on October 5th to see if it has the same forecast idea from the August 5th extension. The Euro was much closer to the current +5 than the CFS.

Sandy was obviously the most extreme since it was such a strong system which occurred at the end of October in 2012. Henri was another much weaker system to come in from the east but was further north than this event. Henri lead to record flash flooding in August 2021. So these much stronger blocks to our north make these type of tracks possible. https://storymaps.arcgis.com/stories/693bb9ddab5b4fb3a4aa5b79e5435b9f