bluewave

Still a long way out to know for sure. The 12Z GEM and UKMET are OTS. The GFS made a shift to the right from 6z. So we’ll have to see what the Euro and AIFS does today. These very strong blocking patterns are tricky for the models to handle. Since there is a fine line between capturing a system and suppressing it offshore.

Even if the PDO goes neutral during the winter, relatively speaking it would be much lower than the +1.70 peak in March 2016 and +1.47 in February 1998. The main difference would be the much warmer West Pacific from Japan to south of the Aleutians. My guess is that this would promote more ridging from east of Japan to perhaps north of Hawaii. Could weaken the Aleutian low and also the low which typically resides near the Southeast US. This could also potentially shift the STJ location. Plus we have seen weaker troughs in general over the last decade and stronger ridges. Very wide spread between the global SST forecast for the February and 1998. So the PDO values might not fully capture the SST difference. Also note how much warmer the Atlantic is forecast to be.

Yeah, near record 588 dm block north of the Great Lakes is very impressive for late September.

Especially if the surface low gets captured by the upper low and gets pulled in from the east by later in the week. Several models have been showing these cyclonic loop scenarios. Still early for details like that but the blocking to the north and closed low are very strong for this time of year. So there is at least some potential.

It got a mention in the recent CPC discussion. Like we have been discussing, could result in weaker low pressure centers with this El Niño. Would fit the recent pattern of overpowering ridges with smaller areas of low pressure. https://www.cpc.ncep.noaa.gov/products/predictions/long_range/fxus05.html There are two factors that make the current situation unique. The first factor is the presence of a fairly strong, negatively phased Pacific Decadal Oscillation (PDO), with the August PDO index value of -1.11 . The "Big Three" historical El Niño's since 1950 include the warm events of 1982-83, 1997-98, and 2015-16, all of which occurred when the PDO phase was positive, leading to constructive interference. This time, however, the PDO phase is negative and may dampen the typical impacts of a strong El Niño in certain areas. The second factor involves the large region of warmer-than-normal SSTs that is typically present in the Gulf of Alaska during strong El Niños. The current situation shows a significant westward shift in these warmer SSTs, which may allow for slightly cooler water to influence portions of the U.S. West coast. In addition, even with the possibility of one or more cold air outbreaks across the northwestern quarter of the Lower 48 states, it is unlikely that this will have much of an impact on the average temperature for a 90-day season.

It’s part of the same pattern which produced the record 600 dm pattern this week. The strength of that ridge may be key to how much rain we actually get this week. Some of the stronger high pressure models like the OP Euro keep most of the rain offshore this week. Other models like the AIFS and CMC have more rain especially near the coast with weaker high pressure to the north. But like we saw with the blizzard in February, the AI and other models beat the Euro which was too suppressed with the coastal low. So this will be a good test of how the AI models handle warm season wavelengths with East Coast lows.

Probably related to how warm the subsurface is from Japan to south of the Aleutians. So every time the PDO rises it meets resistance right around neutral. Will be interesting to see what the ceiling is for the PDO as the super El Niño intensifies going into the late fall and winter. The Euro seasonal maintains the warm pool there through February.

Really unusual fall into spring pattern that year. All-time October warmth followed by not much winter to speak of. Then the record late T of snow in May. Time Series Summary for NEWARK LIBERTY INTL AP, NJ - Month of Oct top 5 warmest maximum temperature Click column heading to sort ascending, click again to sort descending. 1 2019 96 0 2 1941 93 0 3 1949 92 0 4 1959 91 0 5 1939 90 0 - 1938 90 0 - 1908 90 0 Monthly Data for October 2019 for Upton NY NWS CWA Click column heading to sort ascending, click again to sort descending. NJ NEWARK LIBERTY INTL AP WBAN 96 NY LAGUARDIA AIRPORT WBAN 95 NJ HARRISON COOP 95 NJ TETERBORO AIRPORT WBAN 95 NY JFK INTERNATIONAL AIRPORT WBAN 95 NJ CANOE BROOK COOP 94 NJ CALDWELL ESSEX COUNTY AP WBAN 94 NY NY CITY CENTRAL PARK WBAN 93 NY SHRUB OAK COOP 91 CT STAMFORD 5 N COOP 91 NY RIVERHEAD RESEARCH FARM COOP 91 NY MOUNT SINAI COOP 91 NY FARMINGDALE REPUBLIC AP WBAN 90

Depends on the year since the ridge location and intensity has been quite variable during previous super El Niño Octobers. This year is doing its own thing so far with the ridges stronger and further south than usual. We’ll have to see what the pattern looks like in early October since all we have now is a snapshot for the start of the month.

80s have become more common in October during the last decade. We even had November 80s two years during the 2020s. The average for warm spots like Newark has been 4 days reaching 80° past the end of September. Monthly Number of Days Max Temperature >= 80 for NEWARK LIBERTY INTL AP, NJ Oct-Nov Click column heading to sort ascending, click again to sort descending. Mean 3 0 4 2025 4 0 4 2024 4 2 6 2023 6 0 6 2022 0 1 1 2021 5 0 5 2020 0 0 0 2019 3 0 3 2018 3 0 3 2017 5 0 5 2016 3 0 3 First/Last 80° Summary for NEWARK LIBERTY INTL AP, NJ Each section contains date and year of occurrence, value on that date. Click column heading to sort ascending, click again to sort descending. Minimum 02-21 (2018) 09-28 (2020) 181 Mean 03-28 10-18 203 Maximum 04-15 (2024) 11-06 (2024) 2025 03-29 (2025) 85 10-07 (2025) 83 191 2024 04-15 (2024) 83 11-06 (2024) 83 204 2023 04-06 (2023) 83 10-28 (2023) 84 204 2022 04-14 (2022) 88 11-07 (2022) 81 206 2021 03-26 (2021) 84 10-20 (2021) 80 207 2020 03-20 (2020) 80 09-28 (2020) 81 191 2019 04-08 (2019) 80 10-07 (2019) 80 181 2018 02-21 (2018) 80 10-11 (2018) 81 231 2017 04-10 (2017) 82 10-21 (2017) 81 193 2016 03-09 (2016) 82 10-19 (2016) 87 223

I like the Euro monthly forecasts issued on the 5th which have been doing a pretty good job compared to some of the other guidance.

Overlapping forecast signal showing up near the start of October. A more traditional Nino ridge south of Hudson Bay developing. With the lingering mid-latitude ridge underneath.

The continuing record WWBs are making this the strongest east based event for so early in the season.

Yeah, we could see a subtropical or tropical system eventually form next 2 weeks somewhere to our south. Not what the waterlogged parts of the region want to hear. Even if we don’t get a well defined system, the high moisture could lead to heavy downpours with weak lows and stalled fronts.

September 500mb ridge axis continues to be much further south and stronger than past developing super El Niño events. This has lead to the record warmth across the CONUS this month. At the least the trough near the West Coast matches with the other years. But it’s a weaker area of low pressure than 1997.