GaWx

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.

Recon is on the way. Where any possible low level center is found will be very important to say the least.

0Z Euro ens: only very slight E shift and slightly faster; mean landfall is Apalachicola Thu evening; then it goes N into far W GA and then NNW into NE AL. W of GEFS mean.

Hurricane models are way off the chart strong, but are they even useful yet since there’s not yet a definite LLC?

Unlike GFS/Icon, the 0Z Euro doesn’t appear to be shifting E so far. Upper low not shifted E like on those. Landfall Apalachicola late Thu afternoon at 982. Goes near AL/GA line (W of ATL). 12Z went through ATL.

0Z GEFS, with upper low being 250 miles E of 18Z, has its mean landfall 175 miles E of the 18Z’s Pensacola or just E of Apalachicola. The mean then instead of going NNW through AL travels N into SW GA. So, more/fewer members than last run in GA/AL although AL still has a decent # of members.

0Z UKMET vs 12Z is perhaps slightly E/2 mb stronger (985) with landfall still near Apalachicola late Thu evening and then to Atlanta midday Fri: NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 24 HOURS FORECAST POSITION AT T+ 24 : 18.8N 83.0W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 0000UTC 24.09.2024 24 18.8N 83.0W 1002 32 1200UTC 24.09.2024 36 18.9N 84.8W 1002 36 0000UTC 25.09.2024 48 19.7N 85.1W 999 38 1200UTC 25.09.2024 60 21.6N 86.2W 996 41 0000UTC 26.09.2024 72 23.4N 86.3W 992 44 1200UTC 26.09.2024 84 25.9N 85.3W 988 52 0000UTC 27.09.2024 96 29.2N 84.8W 985 46 1200UTC 27.09.2024 108 33.1N 84.1W 990 32 0000UTC 28.09.2024 120 36.7N 85.4W 998 19 1200UTC 28.09.2024 132 39.2N 87.9W 1003 24 0000UTC 29.09.2024 144 39.8N 92.2W 1007 13 1200UTC 29.09.2024 156 CEASED T

0Z CMC similar to 12Z with Apalachee Bay at 973 mb late Thu afternoon followed by Atlanta 981 Thu night.

0Z GFS also looks to come in a good bit E of its prior runs. The upper low, similar to the case for the 0Z Icon, is further E. Confirmed: 948 mb left side of Big Bend late Thu afternoon. Not nearly as far E as Icon and then tracks into N-C GA.

The upper low on the 0Z Icon is way to east of prior runs. Landfall 975 mb just N of Tampa Thu afternoon!

0Z Icon is coming in well to the east of recent runs with the upper low well to the east of prior runs.

Wow, Don, until you posted this I wasn’t even aware of the extreme Sep -NAO about to occur. According to the latest GEFS based NAO forecast (see below), it is expected to bottom out way down near -2.7 at some point during 9/23-5! That would easily exceed the record lowest Sep daily NAO as the current record low is -2.371, set on 9/12/1971. The only other Sep with any sub -2 daily was 1986. The record low for any month is -3.254, set on 10/21/2002. 9/22/24 GEFS based NAO forecast:

18Z GEFS mean: even further west near Pensacola, which is 50 miles W of 12Z, and then N into AL

This 18Z Icon is well E of the 12Z, showing that there’s still (not surprisingly) a lot of uncertainty.

Moderate to low end strong as best as I can tell per DJF.

Who’s dismissing Webb? You’re probably not talking about me, but in case you are I take him with a grain due to several bad misses but I’m not dismissing him. If I did, I wouldn’t have quoted him to bring him into the discussion. Taking with a grain and dismissing are two different things (at least the way I define them). I assume you agree. I take many seasonal forecasts with a grain due to the difficulty in making winter forecasts, especially early.