bluewave

We had a much stronger sea breeze influence this El Niño to La Niña transition summer. So the only spot around NYC metro to reach 40 days like Newark did in 2016 and 2010 was Harrison away from local sea breeze at the airport. To our SW Hightstown away from the sea breeze only needs 2 more to reach 40. Data for January 1, 2024 through August 29, 2024 Click column heading to sort ascending, click again to sort descending. NJ HARRISON COOP 40 NJ NEWARK LIBERTY INTL AP WBAN 33 NJ CALDWELL ESSEX COUNTY AP WBAN 33 NJ TETERBORO AIRPORT WBAN 31 NJ TETERBORO AIRPORT COOP 29 NJ CANOE BROOK COOP 27 Data for January 1, 2024 through August 28, 2024 Click column heading to sort ascending, click again to sort descending. NJ HIGHTSTOWN 2 W COOP 38 PA READING REGIONAL AIRPORT WBAN 37 PA PHILADELPHIA FRANKLIN INSTITUTE COOP 37 PA NORRISTOWN COOP 35 NJ SOMERSET AIRPORT WBAN 35 Data for January 1, 2016 through December 31, 2016 Click column heading to sort ascending, click again to sort descending. NJ CANOE BROOK COOP 49 NJ NEWARK LIBERTY INTL AP WBAN 40 NJ HARRISON COOP 40 NJ TETERBORO AIRPORT WBAN 36 NJ TETERBORO AIRPORT COOP 36 Data for January 1, 2010 through December 31, 2010 Click column heading to sort ascending, click again to sort descending. NJ CANOE BROOK COOP 59 NJ NEWARK LIBERTY INTL AP WBAN 54 NY MINEOLA COOP 52 NJ RINGWOOD COOP 51 NJ HARRISON COOP 50 NY LAGUARDIA AIRPORT WBAN 48 NJ CRANFORD COOP 46 NY BRONX COOP 45 NJ TETERBORO AIRPORT COOP 41 NJ TETERBORO AIRPORT WBAN 40

The competing marine heatwaves angle may be part of the equation. I don’t think it’s a coincidence that the only other recent time this happened was in 2022. Now that the models are forecasting the tropics to become more active in early September something similar happened after a quiet August in 2022. We don’t know yet whether September will manifest in a similar way to 2022, but the record warmth closer to the Gulf is concerning for any storms that can get in there. So far the models are not showing any major hurricanes in the Atlantic basin from August 20th through September 1st. This isn’t a typical occurrence for heading into a La Niña winter. The only other years this happened since 1995 were in 2022 and 2000. While the sample size is very small to draw from, 2022 had a very active September with hurricanes Danielle and Earl reaching cat 1 and cat 2 status. The big stories that month were Fiona going Cat 4 and Ian Cat 5. La Niña years since 1995 major hurricanes August 20th September 1st 2022….none 2021….Ida….Cat 4…..Larry Cat 3 2020…Laura Cat 4 2017….Harvey Cat 4…Irma Cat 5 2016….Gaston Cat 3 2011….Irene Cat 3 2010…Danielle Cat 4….Earl Cat 4 2008….Gaston Cat 4 2007…..Dean….Cat 5 2005…..Katrina Cat 5 2000…..none 1999…..Brett Cat 4….Cindy Cat 4 1998…..Bonnie Cat 3 1995…..Louis Cat 4

One of the few parts of the East that have been really dry just to their west.

First 95° of the season for JFK. THE KENNEDY NY CLIMATE SUMMARY FOR AUGUST 28 2024... VALID TODAY AS OF 0400 PM LOCAL TIME. CLIMATE NORMAL PERIOD 1991 TO 2020 CLIMATE RECORD PERIOD 1948 TO 2024 WEATHER ITEM OBSERVED TIME RECORD YEAR NORMAL DEPARTURE LAST VALUE (LST) VALUE VALUE FROM YEAR NORMAL ................................................................... TEMPERATURE (F) TODAY MAXIMUM 95 227 PM 98 1948 81 14 74 1973 MINIMUM 72 1249 AM 53 1986 66 6 67 AVERAGE 84 74 10 71

August 2024 was the 9th month in the 2020s with over 10.00” of rainfall for at least some portion of the OKX forecast zones. We haven’t had a 5 year period before with this many months over 10.00”. So this is even more impressive than 2003 to 2018. Aug 2024 Mar 2024 Dec 2023 Sep 2023 Jul 2023 Sep 2021 Aug 2021 Jul 2021 Jul 2020 Sep 2018 Aug 2018 Aug 2014 Jun 2013 Sep 2011 Aug 2011 Oct 2010 Mar 2010 Jun 2009 Sep 2008 Apr 2007 Oct 2005 Sep 2004 Jul 2004 Sep 2003 Jun 2003 Monthly Data for August 2024 for Upton NY NWS CWA Click column heading to sort ascending, click again to sort descending. NY PORT JEFFERSON STATION 0.3 SSW CoCoRaHS 15.58 CT NEWTOWN 4.6 SE CoCoRaHS 15.51 NY ST. JAMES COOP 15.49 CT NAUGATUCK 1.7 NNE CoCoRaHS 13.40 CT SOUTHBURY 2.3 W CoCoRaHS 12.83 CT STAMFORD 1.0 S CoCoRaHS 12.70 NY CENTEREACH 1.3 NE CoCoRaHS 12.64 NJ NORTH ARLINGTON 0.7 WNW CoCoRaHS 12.35 CT RIDGEFIELD 2.4 NNE CoCoRaHS 12.29 CT DANBURY COOP 12.27 NY SEAFORD 0.4 SE CoCoRaHS 12.18 CT BETHEL 4.5 SSE CoCoRaHS 12.01 CT RIDGEFIELD 3.7 NNE CoCoRaHS 12.00 CT MONROE 0.8 W CoCoRaHS 11.97 CT RIDGEFIELD 3.6 N CoCoRaHS 11.74 CT NEW CANAAN 3.8 N CoCoRaHS 11.66 NJ MAPLEWOOD TWP 0.9 SE CoCoRaHS 11.59 NY SETAUKET-EAST SETAUKET 0.7 SSW CoCoRaHS 11.54 CT HERITAGE VILLAGE 0.2 E CoCoRaHS 11.17 CT BETHEL 3.5 NNE CoCoRaHS 10.97 NY MOUNT SINAI COOP 10.90 NJ MONTVALE 1.8 ESE CoCoRaHS 10.81 CT BROOKFIELD 3.3 SSE CoCoRaHS 10.81 NJ WANAQUE RAYMOND DAM COOP 10.66 CT BETHEL 0.5 E CoCoRaHS 10.66 NJ OAKLAND 1.0 ESE CoCoRaHS 10.58 NJ CHARLOTTEBURG RESERVOIR COOP 10.50 NJ HARRISON COOP 10.38 CT PROSPECT 1.9 ENE CoCoRaHS 10.28 NJ MONTCLAIR 0.7 N CoCoRaHS 10.22 NJ WAYNE TWP 0.8 SSW CoCoRaHS 10.16 NY SELDEN 1.6 ESE CoCoRaHS 10.13 NJ LITTLE FALLS TWP 0.5 WNW CoCoRaHS 10.12 NJ RINGWOOD 3.0 SSE CoCoRaHS 10.04

Yeah, the quieter Atlantic in late August and that big ridge forecast over Canada to start September matches the MJO 5 composite for this time of year.

The high to the north corrected stronger than originally forecast. So 90s forecast right down to the South Shore beaches with rare WNW flow 90s. One of the few 90s days without onshore flow. Could be the warmest day of the summer for JFK which has only made it to 93° due to all the onshore flow. New run Old run

Yeah, I also believe the record warmth in the Atlantic is enhancing the Southeast Ridge.

It’s also the big changes to the -PDO making it a much warmer pattern than it was before 2014. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022GL101078 The fundamental result of this study is that the first EOF of SST in the North Pacific has changed starting in 2014. For more than 20 years, the PDO has been used to describe the state of the North Pacific. However, since the marine heatwave of 2014, there have been remarkable changes to the dominant mode of SST in the North Pacific. The spatial pattern of the first EOF of SST from 1950 to 2021 is notably different from the PDO, suggesting that though the PDO served as a useful metric of SST variations until 2014 (Johnstone & Mantua, 2014), it may no longer be as effective a climate index for the North Pacific. From 1950 until the 2014 MHW, the first EOF remained consistent in its proportion of positive and negative regions with both taking up roughly half the area of the North Pacific (and with the positive region taken to be the eastern Pacific). When EOFs are calculated from 1950 to endpoints after 2014, the first EOF has a maximum positive region covering 77% of the North Pacific, with a PC indicating the largest anomalies on record. These changes to the first EOF/PC of North Pacific SST are nothing short of remarkable. In concert with these changes, the second EOF/PC of SST has also undergone profound evolution since 2014. This second EOF now accounts for approximately 18% of the variability, growing from 13% during the 1950–2013 period. The spatial structure of the second EOF now is positive over almost the entire basin, with a PC that has grown strongly positive in the last several years. Thus, the second EOF/PC describes warming over much of the Pacific not in the positive lobe of the first EOF. A relevant aspect of our analysis is that we did not remove a trend from the data before calculating the EOFs and PCs. This is consistent with the original calculations of EOFs in the North Pacific (Davis, 1976) and more recent analysis by Johnstone and Mantua (2014), but inconsistent with the definition of the PDO which did have a global mean trend removed (Mantua et al., 1997; Zhang et al., 1997). Whether or not a trend was removed had little effect on the first EOF, and thus the PDO, until 2014. Two of our results lead to this conclusion: first, our first PC calculated between 1950 and 1993 agreed with the PDO with a correlation coefficient of 0.97; and second, our first EOF calculated with successively longer time series did not change in shape until 2014. There are many approaches to removing a trend from time series (Deser & Phillips, 2021; Frankignoul et al., 2017; Solomon & Newman, 2012). We investigated two of these approaches: first we removed a least-squares fit of a line to the global average temperature as in the original definition of the PDO (Figure S2 in Supporting Information S1), and second, we removed a least-squares fit of a line from each grid point in the North Pacific (Figure S3 in Supporing Information S1). In each case the EOF analysis reproduced the PDO spatial pattern and index, suggesting that the PDO remains a good measure for the variability relative to the trend. In general, removal of a trend (as by least-squares fitting of a line, e.g.,) tends to deemphasize the ends of a record. In our analysis, the inclusion of the trend highlights the fact that the warming in the eastern Pacific has increased notably in recent years, a fact that would be obscured if a linear trend had been removed. The PDO is recognized to be a result of many processes that may cause temperature variability (Newman et al., 2016) rather than any singular phenomenon. The many processes that affect SST have apparently combined to create both this era of frequent marine heatwaves beginning in 2014 and a fundamental change to the first mode of SST. The persistence of the marine heatwaves was studied by Di Lorenzo and Mantua (2016) who also invoked a number of interacting processes, suggesting that the variance described by the PDO would increase in a warmer climate. Di Lorenzo and Mantua (2016) explicitly removed a trend before calculating the EOFs of SST, so that their EOFs described variance relative to the trend. The PDO is based on a constant spatial pattern defined by the EOF that described the most variance of SST through the mid 1990's. However, there is no guarantee that the EOFs of SST will remain constant as climate change continues. This concern about indices based on EOFs applies also to the North Pacific Gyre Oscillation (Di Lorenzo et al., 2008), which describes variance in sea surface height. The PDO is widely used as a measure of temperature in the eastern boundary upwelling system along the west coast of North America (e.g., Weber et al., 2021). The period of persistent marine heatwaves since 2014 has made the PDO less useful as an index of temperature in this region because it does not reflect the recent increase. In general, using PCs from a basin-wide analysis as indices of temperature for specific regions may be problematic because the influences from distant parts of the basin affect the PCs. Options moving forward may include: (a) updating the definition of the first mode of temperature variability, as we have done here, (b) explicitly accounting for the trend in addition to the PDO for a measure of temperature, or (c) defining a new temperature metric in a specified area in the region as is done for the various measures of El Niño (Trenberth, 1997) or more recently as in the NEP index (Johnstone & Mantua, 2014). Interestingly, the NEP was first published just before the recent period of MHWs, and the value of the approach championed in Johnstone and Mantua (2014) has only increased. The wide-ranging effects of the recent period of MHWs are likely to be seen in continuing studies of the eastern North Pacific.

The flipside of the more poleward Aleutian ridge dropping the -EPO is also a trough tucked underneath near the West Coast. So deeper lows digging into the West also pump the Southeast Ridge. It was a much safer bet for us in a month like January 2022 when the Aleutian Ridge was able to build into the +PNA region. But most of the time since then the Aleutian Ridge axis is further west near the Dateline which allows more of a trough out West than we want. This is why I have been mentioning a mismatch pattern would be necessary to push back against this predominant winter pattern since the 15-16 super El Niño.

Could also be that a warmer climate supports stronger 500 mb ridges. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015GL066669 Apart from global scale surface warming, anthropogenic forcings also lead to warming and thermal expansion of the lower atmosphere. Here we investigate these effects using the geopotential height at 500 hPa, an indicator of the combined thermodynamic and dynamic climatic response to external forcings. We employ optimal fingerprinting, which uses information from reanalysis data sets and experiments with seven state-of-the-art climate models, to assess the role of anthropogenic and natural influences on changes in the geopotential height during the satellite era. A significant global increase in the annual and seasonal mean geopotential height due to human influence is detected, a result confirmed with four different reanalysis data sets. A more moderate increase in the annual mean associated with natural forcings is also detected. Our findings, consistent with previous detection and attribution studies of changes in temperature and sea level pressure, indicate the prominent role of human influence on some recent climatic changes. Key Points New independent evidence of human contribution to recent climatic changes in the lower atmosphere Human influence is detected in global increases in the 500 hPa geopotential height since 1979 A smaller natural signal is also detected in changes of the annual mean geopotential

The difference between the 98-99 to 07-08 La Niña era and the more recent one since 16-17 is that the Aleutian Ridge and Southeast Ridge have become much stronger.

That’s why I was mentioning the influence of the WPAC warm pool from last spring into fall in the El Niño thread. The stronger Niña-like MJO phases coupled with the -PDO and weakened the Aleutian low and SE US Nino trough we typically see during El Niños. It allowed the Nino Ridge in Canada to grow stronger than usual and press down into the Mid-Atlantic. Notice how the Nino Ridge was even more expansive than the 97-98 super El Niño down into the Midwest and Mid-Atlantic. But the Aleutian low and Southeast Low response was much weaker.

That’s why I mentioned that convection forecasts with backdoors can be tricky. Sometimes the westerly flow ahead of the front instead of SW can limit moisture convergence. So we end up with widely scattered to not much. But on a few occasions we’re were able to manage more widespread severe storms. So probably a nowcast since each model is showing the convection in different locations.

Yeah,record preconditioning of the pack from May into July with strong dipole in tandem with the record -NAO and then the GAC. It’s been very challenging to get all those factors to line up during any summer since then. It will be interesting see how long it will take the Arctic to warm enough were a less hostile pattern for sea ice retention will still result in the 2012 record getting surpassed. https://www.climate.gov/news-features/understanding-climate/five-things-understand-about-ice-free-arctic Obviously, 2012 being below average had a lot to do with the long-term trend. But the fact that it was record-low was due to the weather. Not only did Arctic atmospheric circulation favor sea ice decline in 2012, but there was another contributing factor. The National Snow and Ice Data Center (NSIDC) reported a strong storm centered over the Arctic in August of that year. The storm broke up the Arctic’s sea ice, driving down its extent, although the precise impact of this individual storm remains unclear. Storms are nothing new in the Arctic Ocean, but their influence on sea ice has grown over time. Dániel Topál says, “Weather events and storms definitely play a huge role. Sea ice is getting younger and younger, thinner and thinner.” Arctic sea ice is thinning because less ice survives summer melt seasons. Whereas ice that has survived multiple melt seasons is thick, rough, and resistant to melt, younger ice is vulnerable to storm-induced breakups. The same storm, encountering thicker ice, would likely have had less impact. “I think with the thinner, younger ice that’s in the Arctic now, there is the potential for even more sea ice variability,” Walter Meier says. Several years of [weather] conditions that favor ice growth, or at least ice preservation, would slow the arrival of an ice-free Arctic summer; a few years of extreme melt conditions or a few strong storms could hasten the arrival of ice-free conditions. But, Meier explains, weather conditions can’t be predicted more than about 10 days into the future. Furthermore, scientists don’t have a handle on potential changes in weather systems, such as Arctic storm intensity, that may emerge in coming decades.

While I don’t know whether it will be correct or not with the more poleward extension of the Aleutian Ridge into Alaska than the Euro, we did have a pattern like this in 16-17. Very weak La Niña following the super El Niño in 15-16. Not sure if the CANSIPS may be underestimating the trough out West compared to 16-17 if that poleward extension verified. While it was a mild winter in the East, that poleward extension got us in the game for a better snowfall outcome than the last few seasons. But we have a much stronger -PDO pattern now so not sure if we could do as well in the snowfall department as we did that season. Any improvement in snowfall over the last two seasons would be nice to see.

Another big slowdown in extent losses in August as we have seen in recent years. While there was a record dipole in June, it quickly reversed in July and August. It was enough to cause the lagged steep losses we saw in July. But not enough to surpass 2012 extent in August. The Arctic will probably need more extended dipole patterns in the future in order to surpass the 2012 record as this recent paper found. But long range dipole forecasts beyond 6-10 days aren’t very good. So it’s anyone’s guess when we’ll finally get strong enough May melt pond preconditioning and an extended summer dipole. https://www.woodwellclimate.org/natural-atmospheric-cycle-has-been-stalling-the-loss-of-arctic-sea-ice/ https://nsidc.org/sea-ice-today/analyses/waning-arctic-summer Arctic minimum projection http://nsidc.org/arcticseaicenews/files/1999/08/Projection_Aug18-350x236.png Figure 6. The graph above shows projections of sea ice extent from August 18 through September 30 based on previous years’ observed retreat rates appended to the August 18, 2024, ice extent. Sea Ice Index data. Credit: Walt Meier, National Snow and Ice Data Center High-resolution image As noted above, currently, the sea ice extent stands at fourth lowest for this time of year. We can estimate the extent through the end of the summer using the daily ice loss rates from previous years to project the September minimum extent. This method, which has been regularly contributed to the Sea Ice Outlook, provides a reasonable range of the minimum extent. This year, using the average daily loss rates from 2007 to 2023, the projection starting from August 18 results in a projected minimum of 4.14 million square kilometers (1.60 million square miles), with a range of 3.93 to 4.35 million square kilometers (1.52 to 1.68 million square miles) (Figure 6). This suggests that this year’s minimum will potentially be the third lowest in the satellite record and likely to fall somewhere between the second and eighth lowest. It indicates that a new record low surpassing 2012 is very unlikely.

Looks like mid to perhaps a few upper 90s tomorrow at the usual warm spots. Even the areas from Huntington to Commack can reach these highs with strong westerly flow. Then we get backdoored with much cooler temps and Canadian high pressure to follow. Trying to figure out convection with back doors and westerly flow can be tricky. So will probably be a nowcast event.

We would need a Jan 22 style mismatch pattern in order to avoid the Euro DJF La Nada strong -PDO composite.

Just got my first hail since moving up here. Mostly around .5. But a few larger ones looked closer to .75.

One of the biggest hailstorms of the season to my NE with the cold pool.

The -PDO composite was a great match for this summer. The composites below are for a +PDO pattern in summer and winter. So they have to be reversed. The classic -PDO is a ridge south of the Aleutians and east of New England during the summer. We got one of the strongest ridges on record south of the Aleutians and east of New England. So if this -PDO state continues through the winter then it would feature a strong Aleutian Ridge and Southeast Ridge. Pretty much identical to a robust La Niña 500 mb atmospheric response. We would need to get some type of mismatch like we saw in 21-22 when the MJO 8 shifted us away from the La Niña and -PDO background for January and gave us at least one good winter month even if the winter was still warmer overall the Northeast. Otherwise, the inverse of the below composite would prevail. We probably need to see how things go in October to get some better hints. +PDO summer 500 mb pattern needs to be reversed for -PDO Summer 2024 strong -PDO +PDO winter composite needs to be reversed like summer was

The upper atmosphere warmed faster than the surface leading the record low lapse rates. So this August 20th to 31st is unusually quiet. Last year over the same period we had 6 named storms form. But the record SSTs around the Gulf are concerning since it will only take one wave to get in there and rapidly deepen. So it will be interesting to see how the rest of the season goes as we approach the peak. Hurricane seasons are mostly evaluated on land impacts which are largely unknown until we reach the peak later in the season.

The wild card for ACE this season may be the upper atmosphere warming faster than the surface. So we’ll have to see what happens once we reach the peak of the season in September. This may be why most of the other developing La Niña summers since 1995 had major hurricanes between August 20th and 31st without any this year. Perhaps if the upper atmosphere begins to cool off faster we’ll see an uptick in activity during the coming weeks. The record SSTs in the Gulf are concerning for any waves that can find a way in there since they could rapidly intensity. I know we like to focus on total ACE for judging a season but in actuality it’s mostly about landfall impacts which are usually a big unknown until we reach the heart of the season. So as always it only takes one hitting a populated area to have a big season regardless of ACE or total storm counts. La Niña years since 1995 major hurricanes August 20th September 1st 2022….none 2021….Ida….Cat 4…..Larry Cat 3 2020…Laura Cat 4 2017….Harvey Cat 4…Irma Cat 5 2016….Gaston Cat 3 2011….Irene Cat 3 2010…Danielle Cat 4….Earl Cat 4 2008….Gaston Cat 4 2007…..Dean….Cat 5 2005…..Katrina Cat 5 2000…..none 1999…..Brett Cat 4….Cindy Cat 4 1998…..Bonnie Cat 3 1995…..Louis Cat 4

After the big ACE jump with Beryl earlier in the season the ACE will be closer to average near the start of September. https://kouya.has.arizona.edu/tropics/index.html