GaWx

Atlanta’s record low SLP of 981 mb as well as records for much of the W half of GA will certainly be threatened and some if not many will probably be broken. Many current record lows in central GA E to Augusta are from the Storm of the Century of March of 1993. One correction: lowest recorded GA SLP (GA coast is much lower than 970.5) is way too high. It is in the 950s (1890s). But that’s irrelevant for Helene, of course.

I had a heavy batch of showers that came NW off the ocean here the last hour, the heaviest in at least a couple of weeks. The only other significant rain I’ve had this month was 1.5” during 9/5-8. So, since Aug 20th the only significant rains have been today’s and the rain of 9/5-8. I’ll get the measurement later. This was unexpected as there earlier had been no chance of rain and the models didn’t have it. This is important because I finally had a Storm Shield garage door rubber threshold placed yesterday afternoon by company #2 after waiting for several weeks for company #1 to install it to try to prevent future flooding during heavy rain events after what Debby did last month. It requires 48 hours of dry prior to install so the adhesive would be effective. The appointment had been for this afternoon, but fortunately on Mon I was able to move it up to yesterday. Had I not done that, they wouldn’t have been able to install it today in advance of Helene. Whew! It would have been better to not have any rain today to give more time for the adhesive to set in better. But the rain started 19 hours after install. So, hopefully that was enough time.

It looks like the 0Z Euro has the center crossing Gwinnett County in N GA, E/NE of ATL. The distance from landfall position to E of ATL is ~250 miles and it gets there in only 9 hours on the Euro. That works out to an average of a whopping 28 mph, among the fastest on record for that area! To compare, the very fast moving Opal averaged no more than ~25 mph. Eloise of 1975, which also brought damaging winds well inland to W GA, averaged at ~29 mph.

0Z Euro coming in significantly stronger into the Big Bend at 961 mb! It keeps getting stronger with each run.

0Z UKMET: strongest run yet with 977 mb a few hours before a Thu night Apalachee Bay landfall. Keep in mind that this model tends to be conservative this far out. Helene then goes to far NE GA, well E of ATL.

The latest Euro Weeklies mean went absolutely bonkers for the week of 10/7-13. It has a whopping 340% of 2004-2023 averaged ACE or ~23! (see top image below). This is well over peak week climo of 16, which is 4 weeks earlier! This is easily the single highest week I could recall for any single week of Euro Weeklies for the season to date! The 2nd image shows where the bulk of the activity is expected: Gulf, N Caribbean, Bahamas, Bermuda, and much of the W and C subtropical Atlantic. Going back to 1991, I could find only two seasons with ACE anywhere close to 23 during Oct 7-13: -2018’s ~24 due mainly to Leslie and Michael -2016’s ~18 due to Matthew and Nicole So, the latest Weeklies are calling for Oct 7-13 to be just about tied with 2018 for the most active since 1991. That’s very notable for a 100 member ensemble mean. In addition the run’s mean for the week prior, 9/30-10/6 is at 180% of 20 year climo or 17. So, after Helene and the E MDR get ACE up to ~75, an additional 40 is progged for the subsequent two weeks. That would bring ACE up to ~115 with the last half of Oct and Nov still left. The same run is progging another 15 for 10/14-27, which would get it to 130. If this were to verify closely, a 150ish total season ACE would not be far fetched considering the warmth of the Atlantic and the strengthening Niña.

~40 miles E. Nothing unusual this far out.

The spaghetti plots are of the most recent run of these models. AVN is GFS, UK is UKMET, etc

I assume you realize it. But for those who might not realize it, these are not the 18Z global runs, themselves, as they obviously haven’t come out yet. These tracks are mainly based on 12Z runs.

I’m extra worried that the tornado threat from this in especially the NE sector is going to be high. Is that true? Any thoughts? I haven’t heard much about that yet.

12Z Euro ensemble: stronger mean than recent runs; many members are still ~980 mb in Atlanta vicinity, which doesn’t bode well for N GA; flooding rain and wind could both be major issues there; watch out Atlanta, Athens, and surrounding areas. This could rival Opal’s effects there. Combo of strong storm, very fast mover, upper level environment, and large size would be the reasons for this very rare event should it materialize.

12Z Euro is stronger at landfall than recent runs with 976 Thu evening Apalachee Bay. It gets to ATL just 8 hours later and weakens only to 981, which would be flirting with all-time record low SLP there.

12Z UKMET: E shift and a bit stronger vs 0Z bringing it into Apalachee Bay (instead of near Apalachicola) Thu night; goes to a little E of ATL vs near ATL on 0Z TROPICAL STORM 09L ANALYSED POSITION : 19.5N 83.5W ATCF IDENTIFIER : AL092024 LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 24.09.2024 0 19.5N 83.5W 1003 37 0000UTC 25.09.2024 12 20.0N 85.3W 998 37 1200UTC 25.09.2024 24 21.1N 86.0W 993 40 0000UTC 26.09.2024 36 22.5N 86.3W 989 40 1200UTC 26.09.2024 48 24.7N 85.5W 987 48 0000UTC 27.09.2024 60 28.4N 84.4W 983 51 1200UTC 27.09.2024 72 33.3N 83.3W 986 41 0000UTC 28.09.2024 84 38.1N 84.1W 995 31 1200UTC 28.09.2024 96 37.5N 90.7W 1000 17 0000UTC 29.09.2024 108 36.4N 91.4W 1003 13 1200UTC 29.09.2024 120 35.3N 92.4W 1007 12 0000UTC 30.09.2024 132 CEASED TRACKING

And currently the -NAO is by far the strongest on record for September at below -2.7! The -NAO peak is today and tomorrow.

12Z CMC: 977 Big Bend Thu night, but it only weakens to 978 mb SE of Atlanta! That would be bordering on alltime record low SLPs in that region of GA. The potential damage well inland should not be understated.

12Z GFS: landfall near 975 (weaker than recent runs) Big Bend Thu evening

While wintertime -NAOs became relatively few and far between 1980s-present (only 6 of the last 35 winters and all with sunspots under 35) vs the frequent occurrence of such during the prior 25 winters, summertime -NAOs became frequent over the last 18 summers (2/3 of them). So, the tendencies have been highly seasonal.

Tropical Storm Helene Discussion Number 5 NWS National Hurricane Center Miami FL AL092024 1100 AM EDT Tue Sep 24 2024 An Air Force Reserve Hurricane Hunter measured peak 925-mb flight-level winds of 52 kt to the northeast of the center, which supports an initial intensity of 40 kt. Dropsonde data also indicated that the central pressure is down to 1000 mb. Very recently, data from the plane and one-minute visible satellite imagery indicate that the center has become better defined. Based on these data, the system is being designated as Tropical Storm Helene at this time. Helene is moving a little faster toward the northwest (310/10 kt) as it moves around a mid-level area of high pressure located over Florida and the Southeastern U.S. The high is expected to slide eastward through Wednesday as a deep-layer trough digs southward over the Lower Mississippi Valley. This pattern evolution should cause the system to turn northward and north-northeastward late Wednesday into Thursday. The track guidance is very tightly clustered, which would normally imply high forecast confidence. However, depending on exactly where the center forms could end up shifting the entire guidance suite in future cycles, so it is imperative to not focus on specific landfall locations this far in the future. Satellite trends suggest that the shear over the system is beginning to decrease, and model guidance continues to show relatively low to moderate shear for the next 48 hours or so. In addition, oceanic heat content values are very high, and the system will be moving through an environment of upper-level divergence. Therefore, significant strengthening is anticipated, and the NHC intensity forecast shows the system reaching a peak intensity around 100 kt in 48 hours while over the eastern Gulf of Mexico. There could be some increase in shear around the time the system reaches the coast, given the system's large size, it might only weaken slowly. As a result, there is still a risk that the system could reach the coast as a major hurricane. Helene's forecast radii are at the 90th percentile of hurricane size at similar latitudes. Due to the forecast large size of this system, storm surge, wind, and rainfall impacts will extend well away from the center, particularly on the east side. In addition, the fast forward speed while it crosses the coast will likely result in farther inland penetration of strong winds over parts of the southeastern United States after landfall. FORECAST POSITIONS AND MAX WINDS INIT 24/1500Z 19.5N 84.3W 40 KT 45 MPH 12H 25/0000Z 20.3N 85.2W 50 KT 60 MPH 24H 25/1200Z 21.5N 86.3W 65 KT 75 MPH 36H 26/0000Z 23.2N 86.3W 80 KT 90 MPH 48H 26/1200Z 25.9N 85.4W 100 KT 115 MPH 60H 27/0000Z 29.7N 84.3W 100 KT 115 MPH 72H 27/1200Z 33.9N 83.9W 45 KT 50 MPH...INLAND 96H 28/1200Z 39.7N 86.8W 20 KT 25 MPH...POST-TROPICAL 120H 29/1200Z...DISSIPATED $$ Forecaster Berg

0Z Euro a bit delayed in landfalling on the US vs earlier runs with 985 mb midnight Thu night Big Bend. Still 987 Athens Fri AM meaning hardly any weakening due to moving an avg of 25 mph! ———————— 0Z UKMET: Apalachicola late Thu night then to Atlanta area in only ~12 hours due to moving on average ~25 mph!TROPICAL DEPRESSION 09L ANALYSED POSITION : 18.1N 81.8WATCF IDENTIFIER : AL092024LEAD CENTRAL MAXIMUM WINDVERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS)-------------- ---- -------- ------------- -------------0000UTC 24.09.2024 0 18.1N 81.8W 1003 321200UTC 24.09.2024 12 19.7N 83.9W 1003 360000UTC 25.09.2024 24 19.8N 85.6W 999 361200UTC 25.09.2024 36 21.3N 86.4W 995 410000UTC 26.09.2024 48 22.9N 86.5W 992 391200UTC 26.09.2024 60 24.8N 86.1W 991 430000UTC 27.09.2024 72 28.1N 85.5W 988 521200UTC 27.09.2024 84 31.9N 84.8W 989 370000UTC 28.09.2024 96 37.0N 85.8W 994 241200UTC 28.09.2024 108 40.2N 90.4W 1000 250000UTC 29.09.2024 120 CEASED TRACKING

12z UKMET: similar to 0Z with landfall just E of Apalachicola ~midnight Thu night moving NNE into S GA then curls back NNW into N GA near or just S of Atlanta TROPICAL DEPRESSION 97L ANALYSED POSITION : 16.7N 82.2W ATCF IDENTIFIER : AL972024 LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 23.09.2024 0 16.7N 82.2W 1006 25 0000UTC 24.09.2024 12 18.6N 82.2W 1004 33 1200UTC 24.09.2024 24 18.6N 84.6W 1003 34 0000UTC 25.09.2024 36 19.1N 84.6W 1000 38 1200UTC 25.09.2024 48 20.6N 85.1W 997 46 0000UTC 26.09.2024 60 22.8N 85.4W 992 46 1200UTC 26.09.2024 72 25.3N 85.5W 988 48 0000UTC 27.09.2024 84 28.5N 85.0W 984 53 1200UTC 27.09.2024 96 33.2N 83.9W 988 36 0000UTC 28.09.2024 108 38.1N 85.2W 996 33 1200UTC 28.09.2024 120 39.1N 91.0W 999 26 0000UTC 29.09.2024 132 39.0N 92.2W 1003 13 1200UTC 29.09.2024 144 CEASED TRACKING

They initialized it at 17.6N, 82.0W, which is well to the WNW of that. We’ll see what recon finds this afternoon. This from the just released NHC discussion is probably relevant: “While some mid-level rotation is evident in visible satellite images, surface observations and visible satellite images suggest the low-level circulation remains broad and farther to the southwest.”

Already forecasting 110 mph! Potential Tropical Cyclone Nine Discussion Number 1 NWS National Hurricane Center Miami FL AL092024 1100 AM EDT Mon Sep 23 2024 A broad area of low pressure over the northwestern Caribbean Sea continues to produce disorganized showers and thunderstorms. While some mid-level rotation is evident in visible satellite images, surface observations and visible satellite images suggest the low-level circulation remains broad and farther to the southwest. Nonetheless, the system has a high chance of tropical cyclone formation during the next day or two, and it is likely to bring tropical storm conditions to land areas within the next 36 to 48 hours. Therefore, the NHC is initiating Potential Tropical Cyclone advisories for this disturbance. The initial motion is quite uncertain given the current lack of organization, but the best estimate is northward at about 5 kt. A gradual turn toward the northwest is expected during the next day or so, with the center passing through the Yucatan Channel and into the southern Gulf of Mexico. Thereafter, the system is forecast to accelerate northward across the eastern Gulf of Mexico within the flow between a digging deep-layer trough over the central United States and a ridge over the western Atlantic. This motion should bring the center of the system toward the northeastern Gulf Coast on Thursday. The track guidance agrees reasonably well on this scenario, and the initial NHC forecast lies near the simple and corrected consensus aids. Since the disturbance currently lacks a well-defined center, users are reminded that the average forecast track uncertainty is larger in these situations, and future track adjustments may be required. Given the large size of the tropical-storm-force wind field and fast forward speed that is forecast, storm surge, wind, and rainfall impacts will likely extend well away from the center, particularly to the east of the system. While the system is currently broad and not well organized, the models suggest a more well-defined center should develop during the next day or so. Once the system becomes better organized and develops an inner core, the environmental and oceanic conditions appear favorable for significant strengthening. In fact, the DTOPS statistical guidance shows a 95 percent chance of a 65-kt increase in intensity during the next 72 h, and the hurricane regional models highlight the potential for strengthening to major hurricane intensity. Thus, the NHC forecast shows significant strengthening while the system moves across the eastern Gulf of Mexico, with a 95-kt intensity in 72 h. While this forecast is aggressive, it lies near or slightly below the consensus aids, and future adjustments may be necessary. An Air Force Reserve reconnaissance aircraft is scheduled to investigate the system this afternoon. FORECAST POSITIONS AND MAX WINDS INIT 23/1500Z 17.6N 82.0W 25 KT 30 MPH...POTENTIAL TROP CYCLONE 12H 24/0000Z 18.6N 82.4W 30 KT 35 MPH...TROPICAL CYCLONE 24H 24/1200Z 19.5N 83.7W 40 KT 45 MPH 36H 25/0000Z 20.6N 85.1W 50 KT 60 MPH 48H 25/1200Z 22.1N 86.0W 65 KT 75 MPH 60H 26/0000Z 24.2N 86.0W 85 KT 100 MPH 72H 26/1200Z 27.1N 85.1W 95 KT 110 MPH 96H 27/1200Z 34.0N 83.0W 35 KT 40 MPH...INLAND 120H 28/1200Z 38.5N 87.0W 20 KT 25 MPH...POST-TROPICAL $$ Forecaster Reinhart

BULLETIN Potential Tropical Cyclone Nine Advisory Number 1 NWS National Hurricane Center Miami FL AL092024 1100 AM EDT Mon Sep 23 2024 ...DISTURBANCE FORECAST TO STRENGTHEN OVER THE NEXT FEW DAYS... ...TROPICAL STORM WARNINGS AND HURRICANE WATCHES ISSUED FOR PORTIONS OF MEXICO AND CUBA... SUMMARY OF 1100 AM EDT...1500 UTC...INFORMATION ----------------------------------------------- LOCATION...17.6N 82.0W ABOUT 130 MI...205 KM SSW OF GRAND CAYMAN ABOUT 350 MI...565 KM SSE OF THE WESTERN TIP OF CUBA MAXIMUM SUSTAINED WINDS...30 MPH...45 KM/H PRESENT MOVEMENT...N OR 350 DEGREES AT 6 MPH...9 KM/H MINIMUM CENTRAL PRESSURE...1004 MB...29.65 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: The government of Mexico has issued a Tropical Storm Warning for the Yucatan Peninsula of Mexico from Rio Lagartos to Tulum, and a Hurricane Watch from Cabo Catoche to Tulum. The government of Cuba has issued a Tropical Storm Warning for the Isle of Youth, Artemisa, and Pinar del Rio, and a Hurricane Watch for Pinar del Rio. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Hurricane Watch is in effect for... * Cabo Catoche to Tulum, Mexico * Cuban province of Pinar del Rio A Tropical Storm Warning is in effect for... * Rio Lagartos to Tulum, Mexico * Cuban provinces of Artemisa, and Pinar del Rio, and the Isle of Youth A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area, in this case within the next 24 to 36 hours. A Hurricane Watch means that hurricane conditions are possible within the watch area. A watch is typically issued 48 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous. For storm information specific to your area, please monitor products issued by your national meteorological service. DISCUSSION AND OUTLOOK ---------------------- At 1100 AM EDT (1500 UTC), the disturbance was centered near latitude 17.6 North, longitude 82.0 West. The system is moving toward the north near 6 mph (9 km/h). A northwestward motion is expected on Tuesday and Tuesday night, followed by a faster northward or north-northeastward motion on Wednesday and Thursday. On the forecast track, the center of the system is forecast to move across the northwestern Caribbean Sea and into the southeastern Gulf of Mexico during the next couple of days. Maximum sustained winds are near 30 mph (45 km/h) with higher gusts. Strengthening is expected during the next few days, and the system is forecast to become a hurricane on Wednesday and continue strengthening as it moves across the eastern Gulf of Mexico. * Formation chance through 48 hours...high...90 percent. * Formation chance through 7 days...high...90 percent. The estimated minimum central pressure is 1004 mb (29.65 inches).

Thanks, Don. It will likely drop further tomorrow. The bottom should be tomorrow although a Wednesday bottom can’t be ruled out.

For the time being after a significant recent drop, SST anomalies seem to be in temporary bounce back mode.