donsutherland1

Consistent with the idea that a dry end of August often leads to below normal rainfall during the first week of September and September overall, the latest NBM has further trimmed rainfall amounts from yesterday's runs. Now, it shows some showers on Friday and then Saturday evening into Sunday morning with a frontal passage. Rainfall amounts for both events are light. The latest CFSv2 shows drier than normal conditions through at least its Week 1 and Week 2 forecasts. All said, early on, September appears to be on course for a drier than normal month. Model skill falls off sharply beyond two weeks.

New York City had its coolest August since 2000.

Britain has recorded its hottest summer since records began in 1884, with average temperatures reaching 16.10 °C, the Met Office said today. The figure surpasses the previous 2018 record and runs more than 1.5 °C above the seasonal norm, highlighting the accelerating impact of climate change. Moreover, all of the five hottest summers have occurred since 2000, including three since 2018. The record heat follows searing European summers marked by deadly wildfires in Spain, Greece, Turkey, and Cyprus. Scientists say the blazes were more than 20 percent more intense due to global warming, leaving at least 20 dead, displacing tens of thousands, and burning over one million hectares. Globally, June 1-August 31, 2025 will rank as the third warmest on record on the ERA-5 dataset. It will wind up about 0.1°C warmer than fourth ranked 2019. Globally, every year in the 2020s has ranked among the 8 warmest such periods on record: 2020 (7th), 2021 (8th), 2022 (6th), 2023 (2nd), 2024 (1st), and 2025 (3rd). The most recent June-August not to rank among the 10 warmest such periods was 2015 (11th).

The oefficient of determination for December is very weak (0.013): Here's the scatter diagram: The coefficient of determination is almost zero for seasonal snowfall (almost no relationship) at 0.004: Here's the scatter diagram: For cases when August had a monthly mean temperature below 74°, 41.4% of winters saw 30" or more snow. For all other cases, 37.8% of the following winters saw 30" or more snowfall.

In addition, Islip ranked fourth and White Plains ranked 10th.

Frequency of Measurable Daily Rainfall in September for NYC: Frequency of 1.00" or More Daily Rainfall in September for NYC:

Many parts of the region have seen among their ten driest water years (September 1-August 31) periods: Islip: 33.71" (9th driest) New York City-JFK Airport: 30.71" (6th driest) New York City-LaGuardia Airport: 32.90" (8th driest) White Plains: 33.47" (6th driest) Newark just missed. Its 31.79" ranked as the 11th driest water year. Note: Bridgeport is missing rainfall data, so it was excluded from the list. However, if one added 1"-2" of additional precipitation, its water year would rank between 4th and 6th driest on record.

August 2007 closed without any rainfall during the last 10 days of the month, as was the case this year. September 1, 2007 opened up with a high of 79° and low of 64°; September 2025 began with a high of 78° and a low of 64°. September 2007 would go on to wind up warmer than normal with a mean temperature of 70.3° and drier than normal with monthly rainfall of just 1.81". Before one concludes that 2025 has a near identical twin, even if the outcome winds up similar over all, 2007 went on to see a strong La Niña develop following a preceding El Niño winter. The important point is that there are no "perfect" analogs so to speak. However, one needs larger samples. For example, the idea of a drier than normal September is based on 10 cases with no rainfall during August 22-31. It's just one piece of evidence. That the CFSv2 has swung from a wet to a dry idea increases confidence in that outcome. Should the forthcoming ECMWF monthly data reaffirm the earlier idea of a drier than normal September in the Northeast, confidence would increase further. Of course, the Tropics could always hurl a curve ball, perhaps later this month, that foils such forecasts. For now, with a quiet pattern expected to prevail through the near-term, one can look at some fun coincidences like the one mentioned for 2007. Generally cool and dry conditions will persist through midweek. Highs will generally top out in the upper 70s with lows in the 50s outside New York City and low 60s in New York City. It could turn somewhat warmer late in the week with highs on Thursday through Saturday approaching or reach the lower 80s before another cooler air mass moves into the region. A system could bring some rain on Friday into perhaps Saturday. Rainfall amounts appear likely to be mainly less than 0.50". The ENSO Region 1+2 anomaly was -0.1°C and the Region 3.4 anomaly was -0.4°C for the week centered around August 20. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.45°C and the ENSO Region 3.4 anomaly has averaged -0.28°C. Neutral ENSO conditions will likely continue into early autumn. The SOI was -5.23 today. The preliminary Arctic Oscillation (AO) was -0.084 today.

Unfortunately, the paper doesn't mention the statistical threshold that was used to determine a statistically significant relationship. I suspect that it's far less than a 90% or 95% threshold. Based on the outcomes you posted, which is very mixed, I don't think ACE is a useful predictor. Anecdotally, it may seem to hold some value, but not on a consistent or rigorous basis.

Here's where things currently stand. I expect the drought coverage to increase on Thursday's update:

It's possible that the local climate is moving into a cyclical drier period, even as the overall climate has grown wetter. If so, one might see an increase in underperformance cases. Canada's dryness is more widespread than what is expected, in general, for summer. The climate models don't provide interannual variability, though. Some climate projections from Canada's most recent national assessment in 2019. According to more recent research, summers are expected to see warmer and somewhat wetter conditions in western Canada and warmer drier conditions in both central and eastern Canada according to more recent information. The paper also notes that the climate models have shown a wet bias, so far. Finally, with regard to drought risk, it notes: The highest number of consecutive dry days are clustered in the northern regions of Canada (Fig. S7). Aside from the north, high elevation areas along the Rockies, north-western regions and the Canadian prairies have a higher number of CDD than the rest of the country. Sushama et al. (2010) reported similar results with the highest number of dry days concentrated in northern Canada followed by the Canadian Prairies. Given that Canadian Prairies is already a drought-prone area, future increase in dry spells over the region is concerning as shown by several other studies (Singh et al., 2020; Bonsal and Regier 2006).

That's the only paper I could find related to ACE and the NAO or AO.

Recent guidance has been trimming rainfall prospects for the New York City area during the first week of September. The 9/1 12z NBM now shows just 0.24" for the first week of September with maximum 1-day rainfall of 0.21". These numbers may yet change, but statistically odds favor less than 0.50" following the kind of dry end to August that occurred. Sample size is limited to just 10 cases, so sample size issues might somewhat affect the outcomes. Below is the data: The final CFSv2 forecast from August 31 favored a drier to much drier than normal September in the Northeast.

Since ACE is often brought up with regard to looking ahead to the winter. Here's what the literature has to say. In general, Atlantic hurricane activity has some relationship to the winter NAO. The connection is indirect and expressed through the NAO. High ACE seasons are linked to winters with a tendency for positive NAO. Low ACE seasons are linked to a tendency for a negative NAO. For purposes of assessing ACE, ACE is measured from the start of hurricane season to early September. These relationships are strongest during ENSO neutral winters. Many other factors contribute to the overall winter outcome.

Phoenix concluded its fourth hottest summer on record. All four have occurred since 2020 and all but 2021 since 2020 have ranked among the 10 hottest summers. Climate change is producing hotter summers.

New York City's August and Summer 2025 Summary: Summer 2025 in New York City was marked by stark contrasts, swinging between episodes of intense heat and sharp cool spells. June opened with a string of unusually cool days, before flipping mid-month to extreme heat. July was steadier but still ran warm overall, punctuated by surges into the upper 90s and several multi-day heatwaves. August shifted dramatically, dominated by persistent cool anomalies. Nearly two-thirds of the month ran below normal though a warm spell around mid-month tempered the chill. Overall, August 2025 was the coolest August since 2000. Although Summer 2025 was 0.3° above the 1991-2020 baseline (55% of days above normal) and 1.1° above the 1981-2010 baseline that preceded it, the volatility between unseasonable chill and unseasonable heat was its defining character.

August 2025 is concluding with a mean temperature of 73.7° (2.4° below the 1991-2020 baseline and 1.5° below the 1981-2010 baseline). That is the coolest August since 2000. Numerous locations in the Northeast will finish with among the 10 driest Augusts on records. Data for select sites: Allentown: 1.60" (Tied 9th driest) Boston: 0.83" (tied 4th driest) Islip: 0.53" (4th driest) Manchester: 0.64" (3rd driest) Mount Pocono: 1.42" (8th driest) New Brunswick: 1.33" (8th driest) New York City-LaGuardia Airport (8th driest) Portland: 0.53" (5th driest) Sterling: 0.85" (4th driest) Trenton: 0.82" (4th driest) Washington, DC: 0.20" (1st driest) ***New August Record*** Generally cool and dry conditions will persist through midweek. Highs will generally top out in the upper 70s with lows in the 50s outside New York City and low 60s in New York City. A system could bring some rain on Thursday or Friday. The ENSO Region 1+2 anomaly was -0.1°C and the Region 3.4 anomaly was -0.4°C for the week centered around August 20. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.45°C and the ENSO Region 3.4 anomaly has averaged -0.28°C. Neutral ENSO conditions will likely continue into early autumn. The SOI was -4.61 today. The preliminary Arctic Oscillation (AO) was -0.023 today.

August 2025 will finish with a monthly mean temperature under 73.0° at Baltimore. Here's the full distribution:

Washington, DC is concluding its driest August on record. August 2025 will finish with just 0.20" (5.1 mm) of rain. That will easily surpass the old record of 0.55" (14.0 mm), which was set in 1962. Precipitation records go back to 1871. Daily rainfall August 1962 vs. August 2025 is below.

Following this morning's cool temperatures, much of the region saw their most August days with lows in the 50s in more than a decade: White Plains: Most since 1994 New Haven: Most since 2002 Bridgeport, New York City-Central Park, New York City-JFK Airport, New York City-LaGuardia Airport: Most since 2007 Islip: Most since 2014 Newark: Most since 2024

DCA _ NYC _ BOS ___ ORD _ ATL _ IAH ___ DEN _ PHX _ SEA 0.2 -0.1 0.0 0.4 0.3 0.8 1.8 1.7 3.2

It did. It was an unusually dramatic change.

It is now all but certain that New York City will see no rainfall for the August 22-31 period. Such an outcome favors a drier than normal September. When this was first noted last Sunday, the CFSv2 showed wetter than normal conditions for September. The CFSv2 now shows a drier than normal September:

The coolest air mass so far this season moved into the region last night. The temperature fell into the 50s in New York City and 40s in some outlying areas. Low temperatures included: Atlantic City: 51° Binghamton: 44° Bridgeport: 55° Danbury: 47° Farmingdale: 55° Islip: 56° Montgomery: 45° New Haven: 58° New York City-Central Park: 57° New York City-JFK Airport: 57° New York City-LaGuardia Airport: 59° Newark: 57° Philadelphia: 57° Poughkeepsie: 46° Trenton: 51° White Plains: 53° Tonight will be a similar night. Afterward, temperatures will finish the weekend with highs in the middle and upper 70s under abundant sunshine. Generally cool and dry conditions will persist through the middle of next week. A system could bring some rain on Thursday or Friday. The big weather story next week will be the development of a massive heatdome oer western Canada. Temperatures in parts of British Columbia could challenge the Canadian national September record of 101° (38.3°C) from Windsor, ON that has stood since September 6, 1881. The ENSO Region 1+2 anomaly was -0.1°C and the Region 3.4 anomaly was -0.4°C for the week centered around August 20. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.45°C and the ENSO Region 3.4 anomaly has averaged -0.28°C. Neutral ENSO conditions will likely continue into early autumn. The SOI was +8.01 today. The preliminary Arctic Oscillation (AO) was +0.382 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 100% probability that New York City will have a cooler than normal August (1991-2020 normal). August will likely finish with a mean temperature near 73.7° (2.4° below normal). That would make August 2005 the coolest August since 2000. Supplemental Information: The projected mean would be 1.5° below the 1981-2010 normal monthly value.

Great breakdown by ENSO.