GaWx

This week's Nino 3.4 dropped sharply from -0.4 to -0.9. The OHC remained near -0.9. OLR remains positive. The July SOI of +16.3 was the 11th most positive on record. La Nina continues to be favored for fall/winter per this: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf I agree with this that La Nina is pretty heavily favored for later autumn/winter based on this combination of factors. I think the best chance is for a moderate La Nina. Consider this: Similar 3.4 SST anoms around August 18th and the subsequent winter's ENSO: 2017: -0.5 MLN 2016: -0.5 WLN 2007: -0.6 SLN 2011: -0.8 MLN 2020: -0.8 MLN 2021: -0.9 ?? 2010: -1.2 SLN Also, check out the fall/winter ENSO peak when the prior July SOI was within 5 of the 16.3 of 2021: 12.8 SLN 1998 13.4 MLN 1893 13.6 WEN 1979 14.8 NN 1878 16.3 ?? 2021 16.6 SLN 1955 17.2 WLN 1938 18.7 SLN 2010 19.0 MLN 1910 19.6 NN 1950 20.2 MLN 1879

Henri gets into 2nd place in the list of wettest tropical storm or hurricane at NYC with 8.05” as of 8AM! Sept of 1882, the wettest at 10.63”, was from a TS (storm #4) moving up the east coast and it wasn’t as slow a mover it appears:

Then why does their Twitter that I linked above say that Central Park ASOS had 1.94" 10-11 and 1.84" 11-midnight? Are we talking about the same station? "In addition to being the wettest day since 2014... the 1.94" of rain that fell from 10pm to 11pm at Central Park last night was the wettest hour on record for New York City." "The Central Park ASOS broke the daily maximum rainfall record for 8/21 with 4.45 inches of rain! Most of this rain fell over a 2 hour period, with 1.84 inches falling from 11pm to midnight."

Did Central Park have two hours on 8/21/21 rather than just one that belong at the top of this list? Per the NYC NWS Twitter, NYC got 1.94" 10-11 PM and 1.84" 11PM-midnight:

With Central Park now well over 6" and likely already approaching if not already exceeding 7" with significant rain still falling, there's a high chance based on your chart that Henri later gets to 2nd place with only Sept. of 1882 wetter.

And here is a 0Z UKMET image: Henri is then moving NNW as it just misses the far eastern tip of Long Island

And here is a 0Z UKMET image: Henri is then moving NNW as it just misses the far eastern tip of Long Island:

0Z UKMET: more ominous run for CT/RI/inland MA as it goes NNW to near RI/CT border and then continued NNW into west central MA TROPICAL STORM HENRI ANALYSED POSITION : 29.7N 68.2WATCF IDENTIFIER : AL082021LEAD CENTRAL MAXIMUM WINDVERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS)-------------- ---- -------- ------------- -------------0000UTC 19.08.2021 0 29.7N 68.2W 999 501200UTC 19.08.2021 12 29.5N 70.6W 984 640000UTC 20.08.2021 24 29.4N 72.7W 978 741200UTC 20.08.2021 36 29.7N 74.3W 977 660000UTC 21.08.2021 48 30.6N 74.7W 974 731200UTC 21.08.2021 60 32.7N 73.9W 967 790000UTC 22.08.2021 72 36.1N 72.4W 958 851200UTC 22.08.2021 84 39.9N 71.5W 958 810000UTC 23.08.2021 96 42.0N 72.0W 984 44 (CT/MA border)1200UTC 23.08.2021 108 43.0N 72.4W 1001 250000UTC 24.08.2021 120 43.2N 71.8W 1005 191200UTC 24.08.2021 132 43.8N 69.4W 1007 190000UTC 25.08.2021 144 CEASED TRACKING

0Z UKMET: more ominous run for CT/RI/inland MA as it goes NNW to near RI/CT border and then continued NNW into west central MA TROPICAL STORM HENRI ANALYSED POSITION : 29.7N 68.2W ATCF IDENTIFIER : AL082021 LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 0000UTC 19.08.2021 0 29.7N 68.2W 999 50 1200UTC 19.08.2021 12 29.5N 70.6W 984 64 0000UTC 20.08.2021 24 29.4N 72.7W 978 74 1200UTC 20.08.2021 36 29.7N 74.3W 977 66 0000UTC 21.08.2021 48 30.6N 74.7W 974 73 1200UTC 21.08.2021 60 32.7N 73.9W 967 79 0000UTC 22.08.2021 72 36.1N 72.4W 958 85 1200UTC 22.08.2021 84 39.9N 71.5W 958 81 0000UTC 23.08.2021 96 42.0N 72.0W 984 44 (CT/MA border) 1200UTC 23.08.2021 108 43.0N 72.4W 1001 25 0000UTC 24.08.2021 120 43.2N 71.8W 1005 19 1200UTC 24.08.2021 132 43.8N 69.4W 1007 19 0000UTC 25.08.2021 144 CEASED TRACKING

12Z UKMET: Nantucket to Cape Cod most threatened TROPICAL STORM HENRI ANALYSED POSITION : 29.9N 66.1W ATCF IDENTIFIER : AL082021 LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 18.08.2021 0 29.9N 66.1W 1004 40 0000UTC 19.08.2021 12 29.7N 68.4W 999 51 1200UTC 19.08.2021 24 29.5N 70.6W 987 61 0000UTC 20.08.2021 36 29.5N 72.5W 983 63 1200UTC 20.08.2021 48 30.0N 73.9W 981 65 0000UTC 21.08.2021 60 31.3N 74.3W 976 68 1200UTC 21.08.2021 72 33.7N 73.2W 961 85 0000UTC 22.08.2021 84 37.4N 71.3W 960 81 1200UTC 22.08.2021 96 41.1N 70.2W 962 79 near Nantucket 0000UTC 23.08.2021 108 42.4N 69.9W 986 46 near Cape Cod 1200UTC 23.08.2021 120 43.0N 68.0W 996 35 0000UTC 24.08.2021 132 43.4N 65.5W 1003 27 1200UTC 24.08.2021 144 44.2N 62.5W 1005 25

12Z UKMET: comes slowly west for 3 days and then turns back safely OTS TROPICAL DEPRESSION 08L ANALYSED POSITION : 31.9N 63.0W ATCF IDENTIFIER : AL082021 LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 16.08.2021 0 31.9N 63.0W 1013 23 0000UTC 17.08.2021 12 31.0N 63.2W 1012 24 1200UTC 17.08.2021 24 30.7N 63.8W 1012 25 0000UTC 18.08.2021 36 30.7N 65.0W 1012 26 1200UTC 18.08.2021 48 30.7N 66.6W 1014 26 0000UTC 19.08.2021 60 31.1N 68.2W 1014 25 1200UTC 19.08.2021 72 31.1N 69.6W 1013 25 0000UTC 20.08.2021 84 31.7N 70.1W 1011 27 1200UTC 20.08.2021 96 32.9N 69.9W 1010 29 0000UTC 21.08.2021 108 34.4N 68.4W 1009 30 1200UTC 21.08.2021 120 35.6N 65.7W 1010 29 0000UTC 22.08.2021 132 35.9N 62.3W 1010 29 1200UTC 22.08.2021 144 35.0N 59.1W 1010 30

Indeed, the 0Z EPS had some members threatening the E coast as you showed. However, the 12Z was less threatening.

The 18Z Euro ens goes back to having a few US threats from 96L, similar to the 0Z and 6Z, with 3 members showing a TS+ moving toward the SE US at the end of the run though keep in mind that's only 6% of the members thus making them outliers:

Here's the end of the 18Z Euro. It would likely recurve rather sharply soon after because the 500 mb ridge is then weakening rapidly and prior Euro runs did recurve it then. However, this run is the strongest yet and it is the furthest west. So, even though odds per current models strongly favor a safe recurve, the more important thing here to note may be the Euro trend. Also, how does Grace affect the steering, a possible fly in the ointment? Also, let's see what the 18Z Euro ens members do. The 0Z and 6Z both had a handful of E coast threats (5-10% of the members). Then the 12Z pretty much backed off.

The 12Z Euro ens is back to 96L being hardly any threat to the US.

12Z UKMET gives flooding rainfall from SW GA through SW VA keeping in mind that this is based on a track that’s well east of 11 AM NHC track:

12Z Ukmet is quite a bit east of the NHC forecast track with it crossing the FL/GA/AL point and then moving NNE through GA instead of AL: TROPICAL STORM FRED ANALYSED POSITION : 25.6N 84.6W ATCF IDENTIFIER : AL062021 LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 15.08.2021 0 25.6N 84.6W 1010 30 0000UTC 16.08.2021 12 26.7N 86.0W 1006 36 1200UTC 16.08.2021 24 28.0N 86.1W 1004 35 0000UTC 17.08.2021 36 29.3N 85.8W 1001 38 1200UTC 17.08.2021 48 31.1N 85.0W 1005 30 0000UTC 18.08.2021 60 33.3N 84.0W 1007 24 1200UTC 18.08.2021 72 37.3N 82.3W 1012 15 0000UTC 19.08.2021 84 39.3N 80.2W 1014 25 1200UTC 19.08.2021 96 CEASED TRACKING

This is setting up to bring unneeded heavy rain for the Atlanta area. Most of that area has had above normal rainfall this summer and thus this could be setting them up for flooding concerns. The NHC projected track 100 or so miles to their west and northwest into NE AL is the type of track that often brings them multiple inches of rain within a short period. Fortunately, it looks to not be a slow mover, however (more like average speed for a TC in that area in August).

Any potential east coast threat from 96L may be higher early next week vs late this week. The 6Z Euro ens is similar to the 0Z with again a handful of threatening members out of 51. So, though not a high threat right now (6Z GEFS still says hardly any threat from this), it will be interesting to see whether or not this later evolves into a significant threat, especially NC north:

The 0Z Euro ens says the US E coast may have to watch 96L in about a week as all of those members offshore the SE are from 96L (out of 51 members though): https://i.imgur.com/2tbUJK7.png

Although the 18Z GEFS members are overall weaker than many earlier runs, the 18Z Euro ens has a good number of strong members out of its 51 members with it easily the most active run of today. Also, watch Invest 96L for the possibility that it does something not well modeled that then disrupts the steering flow enough to cause a significant deviation in Grace’s track vs modeling.

The 18Z GEFS started off with all weak members but suddenly became much more active near the SE coast.

18Z GFS is very weak into the Gulf. 18Z GFS ens members so far (hour 90) look weak.

The 12Z Euro ens has only one strong member (out of ~51) landfalling over the SE US and that hits Daytona Beach on 8/21.

More good news with the 12Z Euro having only a very weak low over S FL at 132.