bluewave

This is a continuation of the theme needing record blocking and rainfall to get a briefly cooler pattern. Looks like we go back to the usual warmer near the coast and cooler over the Midwest later August into early September. So more 90° potential for the regular warm spots in NJ. Record blocking north of Hudson Bay with cool down. More 90° heat potential from ensembles for the usual warm spots in NJ Midwest cool and warmer Northeast as we head into September

46° at FOK with the strong radiational cooling. https://www.weather.gov/wrh/timeseries?site=kfok

The MDR SSTs have come down a bit since Beryl but are still high relative to before 2023 which set the second.

The upper low was so strong that today was once of the lowest departures of the year in NYC. Departures of -10 or lower have been pretty rare this time of year. This is even more unusual since the daily departure of -11 isn’t that much lower than the lowest of the year at -12.8 on January 17th. TEMPERATURE (F) TODAY MAXIMUM 73 237 PM 96 1955 83 -10 88 MINIMUM 57 532 AM 53 1922 69 -12 73 AVERAGE 65 76 -11 81 2024-01-17 24 17 20.5 -12.8

You know it’s an impressive cold pool when we are able to get convection with dew points in the 40s this time of year.

The La Niña background state is so strong that it’s actually creating easterly shear in the Atlantic. This is why the models are quiet for late August instead of very active which we usually see during La Ninas. So we’ll have to wait until September for our next period of tropical development. https://michaelrlowry.substack.com/p/the-bell-has-rung-so-why-are-forecast Too much of a good thing? As regular readers of this newsletter know, wind shear – the change in wind direction or speed with altitude – is one of the big hurdles to tropical development. Typically it’s the strong winds at upper levels (30,000-40,000 feet) which blow from west to east (known as upper-level westerlies) through the deep tropical Atlantic and the Main Development Region or MDR that create most of the wind shear issues. So when upper-level winds in the tropical Atlantic turn more east-to-west (easterly winds) and against the west-to-east grain, it usually helps to reduce wind shear, which in turn favors hurricane development. This is especially true during La Niña years like we’re experiencing and when rising air settles in over Africa and the North Indian Ocean as it has recently – a big upper-level disturbance we track across the tropics called the Madden Julian Oscillation or MJO. The combination of La Niña with the part of the MJO that usually reduces wind shear would normally suggest a conducive period for development. However, the upper-level winds have switched so far out of the east that they’re creating easterly wind shear issues across the Atlantic, an unusual problem not often seen in the basin. It means that the MJO will need to move to a less conducive phase to bring back the seasonal upper-level westerlies and tamp down on easterly shear issues plaguing the basin right now. The easterly shear is also worsened by the low-level westerly winds from the northward displaced ITCZ we discussed earlier. The MJO naturally propagates eastward across the globe and extended range models are already showing the easterly shear issues abating toward the end of the month. So when will activity pick back up? Putting all the pieces together, it should be another week or two before the current impediments clear out. It’s possible our next spurt of activity is delayed until the beginning of September, but we should see the transition as August comes to a close late next week. Traditionally 70% of tropical activity, including most hurricane formations, happens from September onward. Still a long way to go in the game, but for now we’ll soak up the unforeseen late August lull.

First time in August since 2012 that the CT Shoreline dropped to 55° or lower as the surrounding sites did. https://www.weather.gov/wrh/timeseries?site=kbdr Time Series Summary for Bridgeport Area, CT (ThreadEx) - Month of Aug Click column heading to sort ascending, click again to sort descending. 2024 55 11 2023 59 0 2022 60 0 2021 60 0 2020 59 0 2019 57 0 2018 59 0 2017 58 0 2016 59 0 2015 60 0 2014 58 0 2013 56 0 2012 55 0

This was one of the strongest La Niña 500 mb summer patterns that we have ever experienced. In our older climate, a La Niña summer 500 mb pattern featured a ridge near Japan and south of the Aleutians. The Atlantic usually had a ridge east of New England. These 3 ridges this summer were some of the strongest we have observed. If this had been the winter with such a strong ridge near the Aleutians and near the East Coast, then it would have been among the warmest on record. So this is telling is that unless we can get some version of mismatch like in January 2022, the winter is going to be very mild again. Probably have to wait until October for some clues to see how the October early MJO indicator evolves. If the winter ridges turn out as exaggerated as the summer, then it will be a very mild winter again. So we need a mismatch along the lines of Jan 2022 with the MJO 8 and more +PNA to counter it. Without pushback we end up with 22-23 warmth again.

Down to 53° here. This was the lowest August temperature for the CT Shoreline since perhaps 2012.

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

Extent is lagging pretty far behind area like we saw in 2016.

Pretty unusual to get a cooldown like this in August with such a strong +AO.

NYC is on track for the first August since 2007 with 2 lows in the 50s.

Very sad what happened there.

Yeah, August 2011 was the most extreme rainfall flooding event for me back in Long Beach. Over 10” of rain during that Sunday morning. Most basements experienced flooding. My 2nd heaviest in a short period of time was 5.00” in 90 minutes during June 1995.

We haven’t been used to getting air flow from near the Arctic in August during recent years.

Several stations over 10.00” for August 2024 including the Bronx mesonet and Centereach in Suffolk along with Bethel in CT. https://www.nysmesonet.org/networks/nyc Thu, Aug 1, 2024 93 75 83 69 82 43 64 0.00 W* 4 17 6:35pm Fri, Aug 2, 2024 92 75 83 72 94 51 70 0.61 S* 5 26 6:00pm Sat, Aug 3, 2024 92 73 80 71 92 48 76 1.44 W 5 28 5:30pm Sun, Aug 4, 2024 84 70 76 70 91 64 81 0.47 SW 6 29 4:30pm Mon, Aug 5, 2024 91 73 82 67 88 36 64 0.00 NW 5 21 5:00pm Tue, Aug 6, 2024 92 71 79 71 95 48 77 5.44 W 6 20 6:35pm Wed, Aug 7, 2024 71 63 66 65 98 86 95 0.15 E 8 28 7:30am Thu, Aug 8, 2024 68 64 67 65 99 84 95 0.36 E 9 24 7:40pm Fri, Aug 9, 2024 82 68 77 73* 100* 77* 89* 0.15 S 12 46 1:55pm Sat, Aug 10, 2024 86 73 79 63 100 38 61 0.00 NW 7 20 1:55am Sun, Aug 11, 2024 82 70 76 56 72 37 51 0.00 W 5 21 10:55pm Mon, Aug 12, 2024 81 67 72 56 80 40 58 0.19 NW 5 20 6:55pm Tue, Aug 13, 2024 81 63 72 56 76 41 58 0.00 NW* 5 16 1:00am Wed, Aug 14, 2024 85 69 76 60 81 34 60 0.00 N* 5 21 4:45pm Thu, Aug 15, 2024 87 68 78 60 77 34 57 0.00 NW* 4 12 4:50pm Fri, Aug 16, 2024 88 71 77 64 84 41 65 0.00 E 5 16 5:00pm Sat, Aug 17, 2024 81 70 74 65 87 56 76 0.02 E 7 25 5:35pm Sun, Aug 18, 2024 81 68 73 69 95 70 86 2.39 SE 7 31 8:05pm Month 93 63 76 65 100 34 71 11.21 6 https://dex.cocorahs.org/stations/NY-SF-84 Today: 9.20" Month-To-Date: 12.05" https://dex.cocorahs.org/stations/CT-FR-43 Today: 6.42" Month-To-Date: 10.60"

Could be the first upper 50s in August this week since 2013 in NYC. Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Aug Click column heading to sort ascending, click again to sort descending. 2024 64 13 2023 63 0 2022 62 0 2021 63 0 2020 62 0 2019 61 0 2018 65 0 2017 60 0 2016 61 0 2015 63 0 2014 61 0 2013 59 0

We usually don’t see scenes like this on Long Island.

Heaviest rainfall event in Suffolk since August 2014. Radar estimates over 10.00” with actual measurements over 8.00” and 9.00”. Looking like more significant damage to roads and residences than 2014 due to the hilly terrain on the North Shore.

Radar estimates over 6”in SW CT with significant flash flooding reported.

Over 4.5” so far.