GaWx

I don’t know whether or not this is related to this thread’s idea of an offshore Mid-Atlantic formation within 4-7 days because it is further S, but I’m posting the 12Z UKMET just in case. The 12Z UKMET has a TC form just offshore the SE US on Thu (9/29) followed by very slow E movement for 3 days due to the blocking high sort of keeping it stuck: NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 102 HOURS FORECAST POSITION AT T+102 : 32.2N 78.8W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 0000UTC 29.09.2023 108 32.5N 77.1W 1011 29 1200UTC 29.09.2023 120 33.3N 76.6W 1010 29 0000UTC 30.09.2023 132 34.8N 75.0W 1010 32 1200UTC 30.09.2023 144 34.4N 74.1W 1009 36 0000UTC 01.10.2023 156 33.4N 73.4W 1007 34 1200UTC 01.10.2023 168 33.1N 72.4W 1005 34

Related to the ridge over troubled waters idea of low pressure forming to the S of NE US/SE Canada high pressure due to lower level convergence leading to rising air and thus LP forming, a good number of 12Z model runs have something within 4-7 days. If over warm enough waters like in this case, it can lead to TCG. The 12Z UKMET does this kind of thing just offshore the SE US on Thu (9/29) followed by very slow E movement for 3 days due to the blocking high sort of keeping it stuck. I don’t know whether or not this is directly related to the @wdragthread idea (thus I’ll probably post this there, too). But whether a system forms as he described it or something further S, a home brew (TC or STC) forming within a week or so just off the E coast seems likely to me: NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 102 HOURS FORECAST POSITION AT T+102 : 32.2N 78.8W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 0000UTC 29.09.2023 108 32.5N 77.1W 1011 29 1200UTC 29.09.2023 120 33.3N 76.6W 1010 29 0000UTC 30.09.2023 132 34.8N 75.0W 1010 32 1200UTC 30.09.2023 144 34.4N 74.1W 1009 36 0000UTC 01.10.2023 156 33.4N 73.4W 1007 34 1200UTC 01.10.2023 168 33.1N 72.4W 1005 34

OHC back down to +0.90 per this:

Today we got an impressive 35th day in a row of a -SOI, which I assume is indicative of atmospheric El Niño coupling. It does appear that the streak will probably end within two days due to rising Tahiti pressures. To compare, the longest -SOI streak for either the 1998-9 through 2000-1 or the 2020-1 through 2022-3 triple La Niña events was only 11 days. The negative correlation of SOI with ONI is high.

I’m not sure why Andy says lower hts over GOM is opposite of ridge over troubled waters. Lower hts over GOM under high hts over NE US/SE Can: how is that opposite when it isn’t?

Sep is looking more like the sluggishly warming June/July rather than the sharp warming of Aug in 3.4. With Sep MTD ~+1.6 as of now, Sep will likely still come out ~0.3-0.35 warmer than Aug, but that’s because Aug started down at only +1.0 to +1.1.

This is continued risk of ridge over troubled waters pt 2 with model consensus suggesting higher than avg TCG chance either NW Car, E GOM or SW Atlantic late next week underneath strong high in SE Can/NE US. 5 of 31 12Z GEFS have strong TS to H.

The Atlantic has had only one TC move W or WNW west of 74W the season to date with none in sight as of now. This is consistent with the map you showed showing a weaker than average Bermuda high/WAR, common during El Niño. So despite the very active season in terms of ACE/# of storms, the tracks have been typical of El Niño.

Regardless of whether or not this becomes a hurricane and assuming no weakening, this is looking to be the strongest storm with a fully nontropical origin to hit the SE US since 2014’s Arthur.

Thanks. Why is the +1.8 F/century in the SE during winter being considered a “warming hole”? Isn’t that about the rate of GW?

Per this chart (thanks to @40/70 Benchmark for posting it elsewhere), the DJF NAO per the model mean is projected to be -0.17. Since I consider -0.25 to +0.25 neutral, this is telling me that the models are favoring a neutral NAO with a negative lean. Although I’ve already said I don’t think there will be a -NAO DJF due to there having been only 6 -NAO during the last 44 winters with one and with all 6 being when DJF sunspots were 33 or lower, a -0.17 is doable imo because of how I define -NAO. The model consensus is calling for a weak -NAO in Feb. with 6 of 9 having weak to moderate. 4 of 9 actually have a weak -NAO in Jan. I currently favor a -NAO in Feb.

Look no further than NYC for some big variability between adjacent winters just since 2010-1: 2010-1: 32.8 2011-12: 40.5 Change was 7.7F Even more impressive: 2014-5: 31.4 2015-6: 41 The change from 2014-5 to 2015-6 was 9.6F, which is the 4th largest change on record between adjacent winters back to 1869-70.

12Z UKMET, like the 12Z GFS and even the 12Z ICON to a lesser extent, has ridge over troubled waters part 2 in about a week: NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 150 HOURS FORECAST POSITION AT T+150 : 31.1N 80.8W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 0000UTC 29.09.2023 156 30.8N 80.4W 1005 34 1200UTC 29.09.2023 168 32.2N 78.1W 1005 30

Strong variability from winter to winter is not going away. It is just that this variability is from a 2F warmer base vs the 1970s.

OHC per this graph back down to under +1.0 and still falling:

With the globe ~2 F warmer than 77-78, do you think there can still be a winter as cold as just 2F warmer than 77-78? For example: Ten coldest Savannah winters since 1875-6: 1977-8: 45.8 (~6BN) 1976-7: 46.0 1957-8: 46.2 1969-70: 46.4 1963-4: 46.6 1962-3: 47.0 1968-9: 47.3 2009-10: 47.8 1980-1: 48.0 2010-1: 48.1 So, if an upcoming Savannah winter were to be 2F warmer than 1977-8, it would be 47.8. That would still be tied for 8th coldest, a top 10 winter. Aside: Note that 7 of the 8 coldest were during El Niño.

Well, the good news for him is that they’re not explicitly predicting a warm winter in his area. They’re literally just saying ~55% chance of AN winter (not far from a coin flip). Furthermore, AN includes just a few degrees AN, which could accommodate a cold Feb. Also, in just over half the lower 48, they’re saying equal chances or only 1/3 chance for AN. For NOAA, the map as a whole doesn’t seem torchy to me. With the way NOAA does these maps, this winter could end up cold in most of the lower 48 and they could correctly claim they weren’t explicitly wrong.

More from the 11AM NHC PTC #16 advisory: WIND: Tropical storm conditions are expected to first reach the coast within the warning area in North Carolina on Friday, and spread northward Friday night and Saturday. RAINFALL: The system is forecast to produce 2 to 4 inches of rainfall, with localized amounts of 6 inches, across the eastern Mid-Atlantic states from North Carolina to New Jersey, Friday through Sunday. This rainfall may produce localized urban and small stream flooding impacts. SURF: Swells generated by this system will be affecting much of the east coast of the United States through this weekend. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office.

BULLETIN Potential Tropical Cyclone Sixteen Advisory Number 1 NWS National Hurricane Center Miami FL AL162023 1100 AM EDT Thu Sep 21 2023 ...LOW PRESSURE AREA EXPECTED TO BRING TROPICAL STORM CONDITIONS AND THE POTENTIAL FOR LIFE-THREATENING STORM SURGE TO PORTIONS OF THE SOUTHEAST AND MID-ATLANTIC COASTS... SUMMARY OF 1100 AM EDT...1500 UTC...INFORMATION ----------------------------------------------- LOCATION...28.7N 75.9W ABOUT 370 MI...595 KM SE OF CHARLESTON SOUTH CAROLINA ABOUT 450 MI...725 KM S OF CAPE HATTERAS NORTH CAROLINA MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H PRESENT MOVEMENT...N OR 10 DEGREES AT 9 MPH...15 KM/H MINIMUM CENTRAL PRESSURE...1012 MB...29.89 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: A Tropical Storm Warning has been issued from Cape Fear, North Carolina, northward to Fenwick Island, Delaware, including Albemarle and Pamlico Sounds, and the Chesapeake Bay south of Smith Point. A Storm Surge Watch has been issued from Surf City, North Carolina to Chincoteague, Virginia, and the for the Chesapeake Bay south of Smith Point, including Albemarle and Pamlico Sounds. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Tropical Storm Warning is in effect for... * Cape Fear NC to Fenwick Island DE * Chesapeake Bay south of Smith Point * Albemarle and Pamlico Sounds A Storm Surge Watch is in effect for... * Surf City NC to Chincoteague VA * Chesapeake Bay south of Smith Point * Albemarle and Pamlico Sounds DISCUSSION AND OUTLOOK ---------------------- At 1100 AM EDT (1500 UTC), the disturbance was centered near latitude 28.7 North, longitude 75.9 West. The system is moving toward the north near 9 mph (15 km/h), and this general motion is expected to continue through early Friday. A north-northwestward to northward motion is forecast by late Friday and continue into the weekend. On the forecast track, the center of the cyclone is expected to approach the coast of North Carolina within the warning area Friday night and early Saturday. Maximum sustained winds are near 35 mph (55 km/h) with higher gusts. Strengthening is expected during the next day or two, and the system is forecast to become a tropical storm as it approaches the coast of North Carolina. Regardless of whether the system become a tropical storm, the system is expected to bring tropical-storm conditions to portions of the southeast and mid-Atlantic coast. * Formation chance through 48 hours...medium...60 percent. * Formation chance through 7 days...medium...60 percent. The estimated minimum central pressure is 1012 mb (29.89 inches). HAZARDS AFFECTING LAND ---------------------- Key messages for this system can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT1 and WMO header WTNT41 KNHC and on the web at hurricanes.gov/text/MIATCDAT!.shtml STORM SURGE: The combination of a dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline. The water could reach the following heights above ground somewhere in the indicated areas if the peak surge occurs at the time of high tide... Surf City NC to Chincoteague VA...2-4 ft Chesapeake Bay south of Smith Point...2-4 ft Albemarle and Pamlico Sounds...2-4 ft South Santee River SC to Surf City NC 1-3 ft Chincoteague VA to Fenwick Island DE...1-3 ft

This is now PTC 16: Potential Tropical Cyclone Sixteen Discussion Number 1 NWS National Hurricane Center Miami FL AL162023 1100 AM EDT Thu Sep 21 2023 A broad non-tropical area of low pressure has formed well east of the east coast of Florida this morning. Although this system is forecast to remain non-tropical during the next 12-24 hours, the dynamical model guidance indicates that it will likely acquire tropical characteristics late Friday and early Saturday as it approaches the coast of North Carolina. Although it is unclear as to whether the cyclone detaches from a front that is forecast to extend northeastward from the center, the guidance suggests a tropical-cyclone like core and structure when it nears the coast. As a result, advisories are being initiated on Potential Tropical Cyclone Sixteen to issue Tropical Storm Warnings and Storm Surge Watches for portions of the coasts of North Carolina, Virginia and Maryland. Winds associated with the front farther north are being covered by non-tropical products issued by local National Weather Service offices and the Ocean Prediction Center. Additional tropical watches and warnings could be issued for other portions of the Chesapeake Bay later today. Since the low is still in its formative stage, the initial motion estimate is a highly uncertain 360/8 kt. The model guidance suggests that center reformations are likely to occur during the next day or so, but the overall motion of the system is expected to be a little east of due north. As the system interacts with a mid-latitude trough that it becomes embedded within, a bend toward the north-northwest is forecast. That motion should bring the center over eastern North Carolina within the warning area Saturday morning. The NHC track forecast follows a blend of the various global models that are in good agreement. The system is forecast to gradually strengthen during the next 24 hours. After that time, the guidance suggests it is likely to form a smaller inner core with additional strengthening expected until the center reaches the coast. The NHC intensity forecast follows the ECMWF and GFS models trends. Key Messages: 1. An area of low pressure is forecast to develop off the southeastern U.S. coast later today and will bring tropical-storm-force winds, storm surge, heavy rain, and high surf to large portions of the southeast and mid-Atlantic United States coast beginning Friday and continuing into the weekend. 2. There is the potential for life-threatening storm surge inundation from Surf City, North Carolina to Chincoteague, Virginia, the Pamlico and Albemarle Sounds, and the lower Chesapeake Bay. Residents in these areas should follow advice given by local officials. 3. Tropical storm conditions are expected within portions of the southeast and mid-Atlantic coasts within the Tropical Storm Warning area beginning on Friday and continuing into Saturday. 4. Heavy rainfall from this system could produce localized urban and small stream flooding impacts across the eastern mid-Atlantic states from North Carolina to New Jersey Friday through Sunday. FORECAST POSITIONS AND MAX WINDS INIT 21/1500Z 28.7N 75.9W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 22/0000Z 30.0N 75.5W 35 KT 40 MPH...POTENTIAL TROP CYCLONE 24H 22/1200Z 31.7N 75.4W 45 KT 50 MPH...POTENTIAL TROP CYCLONE 36H 23/0000Z 33.2N 75.6W 50 KT 60 MPH...TROPICAL CYCLONE 48H 23/1200Z 35.1N 76.4W 50 KT 60 MPH...TROPICAL CYCLONE 60H 24/0000Z 37.3N 76.4W 40 KT 45 MPH...TROPICAL CYCLONE 72H 24/1200Z 38.8N 76.1W 30 KT 35 MPH...POST-TROPICAL 96H 25/1200Z 40.4N 71.8W 25 KT 30 MPH...POST-TROPICAL 120H 26/1200Z...DISSIPATED $$ Forecaster Brown

Whereas 0Z UKMET was 994 mb near Ocracoke, the 6Z UKMET is 992 mb (strongest run yet) ~50 miles further W near Cape Lookout at 5AM EDT Saturday 9/23 and then moves N to 50 miles W of VA Beach at 2PM EDT:

I’m going with a super ONI peak of +2.10 for this contest. This will be fun to follow. The winner(s) should get a free cruise to Nino 3.4 to see those hallowed waters up close and personal!

I was last ~+2.20 for the ONI peak, which was a good bit warmer than my prior strong ONI peak prediction. Based on the slight cooling of the model consensus since last month, I’m lowering my prediction to +2.10 (lower end super Nino). I feel being very slightly warmer than the JMA and a little cooler than the Euro is the best place to be right now.

0Z Euro at 48: strongest run yet at 997 mb 150 mi SE of Wilmington, NC

Now that Sep exact model numbers are out, I can derive the exact model changes from the prior month’s runs: Model: new peak/months (change in peak) BoM: +2.87/DJF (0.00) Met-France: +2.69/NDJ (+0.03) Euro: +2.24/NDJ (-0.16) JMA: +2.06/NDJ (-0.16) UKMET: +1.96/DJF (-0.04) CFSv2: +1.83/NDJ (-0.28) AVG: +2.28/between NDJ and DJF (-0.12)