GaWx

I am not trying to be argumentative in my response here, but I am lost on any correlation, much less causation with respect to sunspot activity and solar influences as inhibiting factors for cyclogenesis. During the same long-duration interseasonal quiet stretch in the Atlantic basin, we saw active stretches in the western and eastern Pacific basins. Solar influences should not discriminate between bodies of water. We have plenty of evidence of phenomenon contained within the troposphere to hypothesize why the Atlantic has struggled versus the WPAC and EPAC. Greater stability across the MDR due to +2-3°C warmer tropopause is among the evidence. But attributing that to sunspot activity seems more of a stretch than SPH placement, MJO, and meridional SSTs negative feedback to counter atmospheric lift versus subsidence. There has been speculation about numerous possibilities. Pro mets as a whole weren’t able to predict the quiet despite the possible factors that you mentioned. Why not? Pro mets are in disagreement as they don’t know. It’s probably from a combo of factors. A very active sun is one possible contributor and a partial negative correlation between solar activity and atmospheric stability (via more heating of upper trop/lower strat) has been hypothesized. Many papers addressing the possible connection have been written since 2008, including those in my post below. Joe D’Aleo was who first brought it to my attention just a couple of weeks ago, but that wasn’t enough as I wanted to see papers. Now I’ve seen them. Thus, I’m now open-minded about this possibility. This graph was put together by Teban at Storm2K. It suggests to me that a ceiling on ACE does seem to be the highest when sunspot number is relatively low.

Yeah, I was wondering about that but dewpoints on 12Z GFS are uniformly warm all around the surface low center. So, GFS looks tropical.

More 12Z: GFS/CMC have a TS form offshore the SE that moves back into S NC to SC/NC border, similar to 0Z Euro, but far different from ICON UKMET has no TC identified in its textual output

The ICON (arguably as good of a global model as any recently) on the new run (12Z) continues to be far different from the model consensus that has a surface low form just off the SE US this weekend into early next week. The ICON continues to develop it well offshore the E US.

Daily sunspot levels Sept MTD: general downward trend has continued. Perhaps the increased activity in the basin is partially related. Keeping an open mind because nobody knows. 2024 09 01 2024.668 182 14.5 27 35 2024 09 02 2024.671 195 21.1 25 32 2024 09 03 2024.673 179 22.2 20 23 2024 09 04 2024.676 174 26.1 21 26 2024 09 05 2024.679 181 13.1 15 20 2024 09 06 2024.682 189 13.3 19 24 2024 09 07 2024.684 167 17.0 22 26 2024 09 08 2024.687 173 17.5 19 24 2024 09 09 2024.690 156 19.9 21 24 2024 09 10 2024.693 149 11.4 20 26 2024 09 11 2024.695 152 15.7 20 23 @Seminole

Not a land threat but a potentially significant ACE producer: Eastern and Central Tropical Atlantic (AL93):Updated: Recent satellite-wind data indicates that the system located a few hundred miles to the west-southwest of the Cabo Verde Islands has developed a well-defined circulation. In addition, showers and thunderstorms continue to show signs of organization, and if these trends continue, advisories will be issued on a tropical depression later this morning. The system is moving to the west-northwest at 10 to 15 mph and will be moving into the central Tropical Atlantic by the end of the week.* Formation chance through 48 hours...high...90 percent.* Formation chance through 7 days...high...90 percent.

From CHS NWS: LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/ HIGH PRESSURE WILL CONTINUE TO EXTEND SOUTH INTO THE REGION EARLY NEXT WEEK. MODELS INDICATE THAT AN AREA OF LOW PRESSURE COULD BE LOCATED WELL OFFSHORE ALONG A STALLED FRONT. THE EVOLUTION OF THIS FEATURE IS STILL UNCERTAIN, SO THERE IS LOWER CONFIDENCE IN THE FORECAST AT THIS JUNCTURE, BUT THE LOW COULD TAKE A TRACK BACK TOWARDS THE SOUTHEAST COAST LATER IN THE PERIOD. MAINTAINED CHANCE POPS EACH DAY, GENERALLY IN THE 30-40% RANGE.

12Z UKMET: landfall now into SE LA, a bit further E vs 0Z; then goes N through E MS and dissipates near KY TROPICAL STORM FRANCINE ANALYSED POSITION : 24.4N 95.8W ATCF IDENTIFIER : AL062024 LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 10.09.2024 0 24.4N 95.8W 996 37 0000UTC 11.09.2024 12 25.9N 94.5W 994 36 1200UTC 11.09.2024 24 27.6N 93.1W 992 44 0000UTC 12.09.2024 36 29.2N 90.5W 989 40 1200UTC 12.09.2024 48 31.4N 89.3W 991 34 0000UTC 13.09.2024 60 34.3N 88.3W 994 24 1200UTC 13.09.2024 72 36.5N 89.1W 999 16 0000UTC 14.09.2024 84 36.6N 88.5W 1005 15 1200UTC 14.09.2024 96 37.7N 87.6W 1009 19 0000UTC 15.09.2024 108 CEASED TRACKING

Can anyone explain why the difference between the cold biased CDAS and the OISST is relatively large currently? It is near the largest of the last few months it appears (0.45): CDAS OISST:

0Z UKMET: similar LA landfall location/strength followed by NNE move to E MS; then N move to far W KY followed by dissipation near IL/IN border TROPICAL STORM FRANCINE ANALYSED POSITION : 24.1N 96.3W ATCF IDENTIFIER : AL062024 LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 0000UTC 10.09.2024 0 24.1N 96.3W 1002 41 1200UTC 10.09.2024 12 24.7N 95.4W 999 35 0000UTC 11.09.2024 24 26.3N 94.2W 995 33 1200UTC 11.09.2024 36 28.4N 92.6W 991 49 0000UTC 12.09.2024 48 30.2N 90.4W 991 37 1200UTC 12.09.2024 60 32.7N 89.5W 995 26 0000UTC 13.09.2024 72 35.3N 89.1W 997 21 1200UTC 13.09.2024 84 36.5N 89.1W 1001 15 0000UTC 14.09.2024 96 37.7N 87.9W 1007 17 1200UTC 14.09.2024 108 38.9N 88.5W 1011 17 0000UTC 15.09.2024 120 CEASED TRACKING

18Z Euro: quite a bit faster as it landfalls at 4PM CDT on Wednesday vs the 12Z’s 11 PM CDT; strength at landfall the same though at 977 mb; keep in mind though that initialization is up at 1003 mb

I continue to think that until it can be proven that it wasn’t the case that the enormous amount of additional water vapor blasted way up into the stratosphere by Hunga Tonga may have had a lot to do with this. Perhaps that combined with the solar max increasing upper tropospheric stability? Who’s to say that this couldn’t possibly have been the case as a major contributor when the cause(s) have yet to be proven?

I assume the NW center is the old 90L former NW Gulf frontal low that’s been dropping S and the other is from the AEW originating 91L, itself. They should soon combine.

12Z UKMET: comes into LA a little further E and slightly stronger (990) vs 0Z (993). Then goes NE to just N of L Ponch. to MS/AL border, where it turns N into W KY. Afterward it turns NE into Indiana, where it finally dissipates: TROPICAL STORM 06L ANALYSED POSITION : 22.7N 93.9W ATCF IDENTIFIER : AL062024 LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 09.09.2024 0 22.7N 93.9W 1004 38 0000UTC 10.09.2024 12 23.8N 95.7W 1000 39 1200UTC 10.09.2024 24 24.8N 95.3W 998 39 0000UTC 11.09.2024 36 26.5N 94.2W 994 35 1200UTC 11.09.2024 48 28.3N 92.4W 992 46 0000UTC 12.09.2024 60 30.3N 90.0W 990 37 1200UTC 12.09.2024 72 32.6N 88.8W 994 29 0000UTC 13.09.2024 84 35.6N 88.3W 996 20 1200UTC 13.09.2024 96 36.9N 88.7W 1000 16 0000UTC 14.09.2024 108 38.1N 87.0W 1006 27 1200UTC 14.09.2024 120 40.0N 86.8W 1009 21 0000UTC 15.09.2024 132 40.1N 86.7W 1010 18 1200UTC 15.09.2024 144 CEASED TRACKING

Below are the daily sunspot #s for Sept MTD. Despite still being high, there’s been a modest trend downward. To compare, Aug was way up at 215, the highest in Aug of the modern active era. There is support from many papers written since 2008 suggesting a partial negative correlation between sunspot #s and overall Atlantic tropical activity. The idea is that the upper troposphere and lower stratosphere are quickly warmed more than below when the sun is more active. This results in increased atmospheric stability, which is less conducive to tropical convection. I wouldn’t consider the connection proven, but I’m open-minded about it. One of the theories being circulated about the very quiet late Aug/early Sep is the very high sunspot #s likely being one of the major contributors to the quiet. With Francine today being designated along with the MDR having increased convection, I do wonder if there could be a partial connection to the very recent moderate reduction in solar activity. Even if there is, the sunspots could quickly rise back one day soon: 2024 09 01 2024.668 182 14.5 27 35 2024 09 02 2024.671 195 21.1 25 32 2024 09 03 2024.673 179 22.2 20 23 2024 09 04 2024.676 174 26.1 21 26 2024 09 05 2024.679 181 13.1 15 20 2024 09 06 2024.682 189 13.3 19 24 2024 09 07 2024.684 167 17.4 21 25 2024 09 08 2024.687 173 17.3 17 22 2024 09 09 2024.690 158 21.2 17 18

Tropical Storm Francine Discussion Number 4 NWS National Hurricane Center Miami FL AL062024 1000 AM CDT Mon Sep 09 2024 The structure of the system on satellite imagery has improved this morning, with a large circular region of cold convection between -70 to -85 near the estimated center. An Air-Force Reconnaissance Aircraft is sampling the system this morning and earlier found a cyclonic wind shift from southeasterly to northwesterly flow near the center of the mass of deep convection. This data provides enough evidence that a well-defined circulation now exists, and thus PTC Six has become Tropical Storm Francine with sustained winds of 45 kt this advisory. The estimated motion is still tricky given the center only recently formed but is estimated still off to the north-northwest at 340/4 kt. The system is expected to gradually turn northward and then north-northeastward as it moves between a mid-level ridge centered over Cuba and a broad mid- to upper-level trough located to its northwest over Texas. The guidance this cycle has shifted a little eastward and faster, and the NHC track forecast was once again nudged in that direction. The current track splits the difference between HCCA and TVCN and still shows Francine moving ashore of Louisiana sometime on Wednesday evening. There remains a decent amount of track uncertainty with the GEFS and EPS ensembles showing along-track spread implying some speed differences near landfall. While the system is now a tropical storm, the inner core wind field per reconnaissance observations is still broad and in the organizing stage, and initial intensification will be gradual. However, after an inner-core becomes established, and assuming the cyclone's vertical structure becomes aligned, a period of more significant intensification is possible while storm is embedded in a low shear, high mid-level moisture, and over very warm 30-31 C sea-surface temperatures. The SHIPS rapid intensification (RI) indices are pretty elevated, and a period of RI could also occur between 24-48 h. For now, the NHC intensity forecast will not explicitly forecast RI, but is higher than the previous cycle and shows a 75 kt peak in 48 h, in good agreement with the intensity consensus aids. After that period, southwesterly vertical wind shear quickly increases from 10 kt to more than 30 kt and the intensity could plateau as it approaches the northwestern U.S. Gulf coastline, though the system is forecast to remain a hurricane at landfall. The NHC intensity forecast continues to be in good agreement with the consensus aids, but is a bit under the HAFS-A/B and COAMPS-TC models. FORECAST POSITIONS AND MAX WINDS INIT 09/1500Z 23.0N 94.9W 45 KT 50 MPH 12H 10/0000Z 24.0N 95.4W 50 KT 60 MPH 24H 10/1200Z 24.9N 95.7W 55 KT 65 MPH 36H 11/0000Z 26.3N 95.0W 65 KT 75 MPH 48H 11/1200Z 28.0N 93.5W 75 KT 85 MPH 60H 12/0000Z 29.7N 92.2W 75 KT 85 MPH...ON THE COAST 72H 12/1200Z 32.4N 90.7W 35 KT 40 MPH...INLAND 96H 13/1200Z 36.2N 89.6W 25 KT 30 MPH...POST-TROPICAL 120H 14/1200Z 37.5N 88.8W 20 KT 25 MPH...POST-TROPICAL $$ Forecaster Papin

WTNT31 KNHC 091455TCPAT1BULLETINTropical Storm Francine Advisory Number 4NWS National Hurricane Center Miami FL AL0620241000 AM CDT Mon Sep 09 2024...DISTURBANCE BECOMES TROPICAL STORM FRANCINE......EXPECTED TO INTENSIFY WITH STORM SURGE AND HURRICANE WATCHESISSUED FOR THE LOUISIANA COAST...SUMMARY OF 1000 AM CDT...1500 UTC...INFORMATION-----------------------------------------------LOCATION...23.0N 94.9WABOUT 245 MI...395 KM SE OF MOUTH OF THE RIO GRANDEABOUT 480 MI...770 KM SSW OF CAMERON LOUISIANAMAXIMUM SUSTAINED WINDS...50 MPH...85 KM/HPRESENT MOVEMENT...NNW OR 340 DEGREES AT 5 MPH...7 KM/HMINIMUM CENTRAL PRESSURE...1002 MB...29.59 INCHESWATCHES AND WARNINGS--------------------CHANGES WITH THIS ADVISORY:A Storm Surge Watch has been issued from east of High Island, Texas, eastward to the Mississippi/Alabama Border, including Vermilion Bay, Lake Maurepas, and Lake Pontchartrain. A Hurricane Watch has been issued from Cameron eastward to GrandIsle in Louisiana.A Tropical Storm Watch has been issued east of High Island, Texas, to Cameron, Louisiana, and from Grand Isle, Louisiana, to the Mouth of the Pearl River including Lake Pontchartrain and Lake Maurepas.

Per this Francine is about to be designated: AL, 06, 2024090912, , BEST, 0, 227N, 947W, 45, 1002, TS, 34, NEQ, 40, 100, 140, 140, 1008, 180, 70, 0, 0, L, 0, , 0, 0, FRANCINE, S, 0, , 0, 0, 0, 0, genesis-num, 014,

0Z Euro: not quite as strong as 12Z with 983 (vs 979) mb at LA landfall; like 12Z goes to Memphis area at 997 mb

0Z UKMET: lowest SLP (993) slightly higher than 12Z; similar landfall location and slightly earlier (late afternoon Wed 9/11); goes a little E of Memphis (slightly E of 12Z); then NE into KY: NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 12 HOURS FORECAST POSITION AT T+ 12 : 22.3N 93.8W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 09.09.2024 12 22.3N 93.8W 1004 35 0000UTC 10.09.2024 24 23.8N 94.9W 1003 34 1200UTC 10.09.2024 36 24.8N 95.2W 1000 37 0000UTC 11.09.2024 48 26.4N 94.0W 996 37 1200UTC 11.09.2024 60 28.5N 93.0W 993 45 0000UTC 12.09.2024 72 30.3N 90.9W 993 33 1200UTC 12.09.2024 84 32.8N 90.4W 995 24 0000UTC 13.09.2024 96 35.0N 90.0W 997 23 1200UTC 13.09.2024 108 35.6N 89.3W 1003 13 0000UTC 14.09.2024 120 36.7N 87.7W 1008 14 1200UTC 14.09.2024 132 CEASED TRACKING

But PT6 would already be the 3rd H landfall on the US if it landfalls as an H and only at the halfway point. The record is 6 for entire season. When you get to 5-6, there are only a relative few seasons with that many. Just getting 3 puts it above average for the entire season.

Ironically considering how this season so far has appeared to many: IF this were to hit the US as a H and based on the model consensus timing, it would be the earliest 3rd H hit on the CONUS since way back in 2005! Only 10 of 173 years since 1851 (6%) would have had an earlier 3rd H hit with only 2 of those during the internet era. They are 2005, 2004, 1985, 1934, 1933, 1916, 1893, 1886, 1879, and 1871. So, in this way at least, not at all a quiet season so far. Edit: Oops, I somehow left off 2020, which had its 3rd US H landfall on LA on 8/27 from Ida. So, it hasn’t been since 2005. Revises it from 10 to 11 of the 173 years (still 6%) with #3 before the expected upcoming LA landfall.

12Z Euro: much stronger, quicker, and further E at landfall than prior runs with 978 mb H at late Wed evening C LA landfall, similar location/timing to 12Z UKMET. It then like the UK turns NNE up/near the Miss River.

After having had no measurable rain for 2.5 weeks, I’ve gotten at least the better part of 1” over the last few days and it’s still raining. Been raining all day so far. Will update with final total later. Along with todays rain are cool temperatures of only low 70s. Ocean temps have cooled nicely from mid 80s a week ago to upper 70s/low 80s now. Autumn is on the way! Final total for 9/5-8: ~1.5”, first rains since 8/20.

12Z UKMET: similar C LA landfall location/timing (PM of 9/11) to 0Z run but stronger at 990 mb vs 996 mb (winds of 40 knots too light imo but that’s a model bias this far out). Also, this run then goes NNE up Miss River to Memphis instead of NE to far E TN: TROPICAL STORM 91L ANALYSED POSITION : 20.2N 93.8W ATCF IDENTIFIER : AL912024 LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 08.09.2024 0 20.2N 93.8W 1004 37 0000UTC 09.09.2024 12 20.4N 93.9W 1003 36 1200UTC 09.09.2024 24 21.8N 94.2W 1003 40 0000UTC 10.09.2024 36 23.1N 94.9W 1002 39 1200UTC 10.09.2024 48 24.7N 95.8W 999 40 0000UTC 11.09.2024 60 25.6N 95.3W 995 35 1200UTC 11.09.2024 72 27.7N 93.6W 990 49 0000UTC 12.09.2024 84 29.8N 91.2W 990 40 1200UTC 12.09.2024 96 32.7N 90.8W 992 27 0000UTC 13.09.2024 108 35.0N 90.2W 995 22 1200UTC 13.09.2024 120 36.3N 89.5W 1002 16 0000UTC 14.09.2024 132 37.4N 88.8W 1007 19 1200UTC 14.09.2024 144 CEASED TRACKING