donsutherland1

Some model guidance has periodically shown a 90° or above temperature for the New York City area after September 15th. The forecast AO-/PNA- combination has seen a disproportionate share of such events. However, these are infrequent events, so a lot more would need to be seen before it is evident that such an event is likely. 90° or Above Highs after September 15th (1980-2024): New York City-Central Park: 7 days New York City-JFK Airport: 6 days New York City-LaGuardia Airport: 12 days Newark: 18 days One would need to see consistent guidance on multiple models with good run-to-run consistency. A big caveat this September is the fact that the ECMWF/EPS has been running a strong warm bias in the 2-5-day range. Moreover, in the cases of New York City and Newark, 80% of the years that saw such late-season 90s had warmer first halves of September than will be the case in 2025. At LaGuardia, 78% of such years had warmer first halves of September. At JFK, that percentage was 83% of years. The most prominent notable exception that followed a cooler first half of September was 2017, which occurred to a highly amplified pattern. Currently, a 2017-type pattern is not showing up on the ensembles. In sum, unless there are some fairly dramatic changes, a 90° or above high in the New York City area during the second half of September appears unlikely. Newark has the best shot on Friday, but could fall several degrees short.

Areas for which I have data: September 1-14: Mount Pocono: 2024: 1.49"; 2025: 0.15" Scranton: 2024: 0.42"; 2025: 0.96" Sussex: 2024: 1.13"; 2025: 1.61" Year-to-Date: Mount Pocono: 2024: 66.61"; 2025: 43.47" Scranton: 2024: 48.65"; 2025: 35.70" Sussex: 2024: 46.60"; 2025: 27.93"

China experienced its hottest summer on record this year. Northern China saw its longest rainy season since 1961. Both developments could share the same atmospheric culprit: a jet stream locked in place. The phenomenon, known as quasi-resonant amplification (QRA), creates stalled wave patterns high above the planet that can trap weather systems for weeks, driving extremes on the ground. QRA works as follows: Arctic amplification (the Arctic warming faster than lower latitudes) reduces the usual north–south temperature gradient that drives the jet stream. A weaker gradient tends to slow and meander the jet stream, allowing large Rossby waves to form. Under certain conditions, Rossby waves with specific wave numbers (typically 6–8) can enter a quasi-resonant state, meaning they grow in amplitude and become trapped, producing near-stationary weather systems. When this happens, regions under ridges experience extended heat and drought, while those under troughs face prolonged storms and flooding.

Temperatures will top out in the upper 70s to perhaps lower 80s tomorrow and then the lower to middle 70s on Tuesday and Wednesday. Readings will likely return to the upper 70s on Thursday and the lower 80s on Friday. Cooler air should return for the weekend. In terms of near-term precipitation, a cutoff system near the Delmarva could bring some showers or a period of rain on Wednesday into Thursday. Parts of the Delmarva and Jersey Shore will likely see the heaviest amounts. September 1-15 remains on track to achieve a solid cool anomaly. Since 2000, there have been nine years that saw a cooler than normal first half of September. Two-thirds of those years went on to record a warmer than normal second half of September. Only two of those years (2017 and 2019) wound up with a monthly mean temperature of 70.0° or above. Overall, for two-thirds of those years, the cool start was sufficiently cool to produce a cooler than normal monthly anomaly. The last year that saw both a cooler than normal first half and second half of September was 2009. Prior to that, it was 2001. The last year to record a cooler than normal first half of September followed by a warmer than normal September was 2024. The ENSO Region 1+2 anomaly was -0.3°C and the Region 3.4 anomaly was -0.4°C for the week centered around August 27. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.33°C and the ENSO Region 3.4 anomaly has averaged -0.32°C. La Niña conditions will likely develop during mid- or late-autumn. The SOI was -9.21 yesterday. The preliminary Arctic Oscillation (AO) was -0.079 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 56% probability that New York City will have a cooler than normal September (1991-2020 normal). September will likely finish with a mean temperature near 68.9° (0.3° below normal). Supplemental Information: The projected mean would be 0.9° above the 1981-2010 normal monthly value.

Here you go:

Despite the dry end to August, precipitation is running above normal in parts of the region through the first two weeks of September and much above the amount for last year in all areas. 2025 is September 1-13 precipitation, but none is expected today. While this does not ensure that the month will finish above normal, it is a welcome development.

For reference, the ECMWF and EPS have been running a fairly strong warm bias in the short range. Meanwhile, the ECMWF continues to rank first in 500 mb anomaly scores: This divergent outcome is a reminder that there is more to forecasting than 500 mb maps. All the details matter. In terms of specific numbers, below were the 9/12 0z EPS forecast highs for Central Park: September 13: 80 (actual: 77) September 14: 86 September 15: 83 September 16: 82 September 17: 83 September 18: 84 September 19: 81 Below were the 9/12 0z ECMWF forecast highs for Central Park: September 13: 80 (actual: 77) September 14: 86 September 15: 84 September 16: 82 September 17: 86 September 18: 90 September 19: 87 Today could reach the lower 80s, tomorrow may reach 80°, Thursday has a shot at 80°, and Friday could be the warmest day, reaching the lower and maybe middle 80s. Interior sections of NJ will be warmer and Friday could see upper 80s there.

Greenland saw a significant rain event this year. From the NSIDC: Substantial rainfall reached the South Dome (SDM) weather station at an elevation of 2,895 meters (9,498 feet) above sea level, with more than 30 millimeters (1 inch) recorded at the SDM weather station on August 14 and 15, per Denmark’s Programme for Monitoring of the Greenland Ice Sheet (PROMICE) (Figure 3b). This is an exceptional amount of rain at this altitude. A similar amount of rain, 29 millimeters (1.14 inches) over August 14 and 15, was also recorded above Nuuk at the NUK_U weather station, at an elevation of 1,122 meters (3,680 feet). In later warm-front pulses during the melt event, the weather station at Swiss Camp recorded 4 millimeters (0.16 inches) of rain on August 18. Earlier, the Swiss Camp station recorded 10 millimeters (0.4 inches) of rain during the mid-July melt event. The first important rain event observed at Summit Station occurred on August 14, 2021. Both rain and surface melting occurred at the same location.

It's more common than one might expect. Here's the data for winters 1979-80 through 2024-25:

Through today, September 2025 has seen just two days with highs of 80° or above in Central Park. The last time there were as few such days during the September 1-13 period was 2009. Tomorrow will be somewhat warmer with widespread highs in the lower 80s. Temperatures will top out in the upper 70s to perhaps lower 80s on Monday and Tuesday. Similar conditions could prevail on Wednesday and Thursday. A cutoff system near the Delmarva could bring some showers or rain to parts of the Jersey Shore and eastern Long Island on Wednesday into Thursday. September 1-15 remains on track to achieve a solid cool anomaly. Since 2000, there have been nine years that saw a cooler than normal first half of September. Two-thirds of those years went on to record a warmer than normal second half of September. Only two of those years (2017 and 2019) wound up with a monthly mean temperature of 70.0° or above. Overall, for two-thirds of those years, the cool start was sufficiently cool to produce a cooler than normal monthly anomaly. The last year that saw both a cooler than normal first half and second half of September was 2009. Prior to that, it was 2001. The last year to record a cooler than normal first half of September followed by a warmer than normal September was 2024. The ENSO Region 1+2 anomaly was -0.3°C and the Region 3.4 anomaly was -0.4°C for the week centered around August 27. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.33°C and the ENSO Region 3.4 anomaly has averaged -0.32°C. La Niña conditions will likely develop during mid- or late-autumn. The SOI was -9.21 today. The preliminary Arctic Oscillation (AO) was +0.225 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 53% probability that New York City will have a cooler than normal September (1991-2020 normal). September will likely finish with a mean temperature near 69.0° (0.2° below normal). Supplemental Information: The projected mean would be 1.0° above the 1981-2010 normal monthly value.

Here are two relevant papers: https://www.nature.com/articles/s41561-019-0310-1 https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2025GL114882

I would only note that even as the current geoengineering effort started off unintentionally, given the state of today's knowledge, the continuation of it is intentional.

I've seen figures of about 75% should all the ice melt. That's not going to happen anytime soon. Even in the Mid-Pliocene, some ice was retained. An Eocene-type scenario would be a different ballgame. Removing even a modest amount of water could disrupt the water cycle, reducing rock weathering (allowing even more CO2 to pile up in the atmosphere) and producing devastating to catastrophic ecosystem damage. Draining the water could also reduce the oceans' thermal inertia leading to faster warming at each level of CO2. Finally, humanity is already engaged in a colossal geoengineering experiment in which it is pumping CO2 into the atmosphere at an order of magnitude or more above the rapid rise in CO2 that sparked the Paleocene-Eocene Thermal Maximum. Given its reckless ongoing conduct in the face of now full knowledge of the consequences of its geoengineering initiative, my guess is that humanity would ignore potential risks in any new geoengineering effort, probably compounding the damage rather than mitigating it. After all, if they ignore the hazards of their current practices, why would any other geoengineering effort be different?

Yes. The temperature has reached 41 on August 28 and September 8-9.

Investments that would dramatically increase renewables beyond leaving things mainly to the private sector would yield large increases in supply. The cost argument isn't a strong defense. It exists only because the kind of approach to infrastructure that took place in building the nation's highways was not pursued.