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Subtropical Storm Alpha Forecast Discussion Number 1

2020-09-18 18:34:41| National Hurricane Center (Atlantic)

Issued at 430 PM GMT Fri Sep 18 2020 000 WTNT44 KNHC 181634 TCDAT4 Subtropical Storm Alpha Special Discussion Number 1 NWS National Hurricane Center Miami FL AL242020 430 PM GMT Fri Sep 18 2020 The small low pressure area that has been rotating around a larger extratropical low in the far northeastern Atlantic has become better organized this morning. Moderate-to-deep convection has persisted near the center since last night, scatterometer data shows a closed 40-kt low, and radar images from Portugal show a definite organized convective pattern. While the system is still in the cyclonic envelope of the large extratropical low and likely neutral- or cold-core, it has developed enough tropical characteristics to be considered a subtropical storm. The initial intensity is set to 45 kt in accordance with the scatterometer data, assuming some undersampling for this small system. Little change in strength is forecast until landfall in Portugal during the next couple of hours. Global models show the small low moving northeastward at about 15 kt for the next 24 hours before dissipating over northern Spain or the Bay of Biscay. The track and intensity forecasts are consistent with the consensus guidance. Additional information on the hazards from this system can be found in products from the Portuguese Institute for Sea and Atmosphere at www.ipma.pt. FORECAST POSITIONS AND MAX WINDS INIT 18/1630Z 39.9N 9.3W 45 KT 50 MPH 12H 19/0000Z 41.5N 7.5W 30 KT 35 MPH...POST-TROP/INLAND 24H 19/1200Z 44.2N 4.2W 30 KT 35 MPH...POST-TROP/EXTRATROP 36H 20/0000Z...DISSIPATED $$ Forecaster Blake

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Hurricane Teddy Forecast Discussion Number 25

2020-09-18 16:50:38| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Fri Sep 18 2020 000 WTNT45 KNHC 181450 TCDAT5 Hurricane Teddy Discussion Number 25 NWS National Hurricane Center Miami FL AL202020 1100 AM AST Fri Sep 18 2020 There was little change to the structure of Teddy since early this morning up until the past hour or so, when the eye began to fill in slightly while the cloud tops over the southern portion of the circulation warmed a bit. However, new convection with very cold cloud tops near -80 degrees C have developed recently over the northwestern quadrant, so the cyclone could just be undergoing a temporary intensity fluctuation that typically occurs in powerful hurricanes. The latest Dvorak intensity estimates range from 102 kt to 116 kt, and the initial intensity is being held at 115 kt for this advisory. There will be staggered NOAA and U.S. Air Force Reserve Hunter aircraft investigating Teddy starting this morning and continuing into the late afternoon, so they will soon be able to provide updated details on the latest structure, size, and intensity of the hurricane. The major hurricane continues to move northwestward, now at 10 kt. Teddy is expected to remain on that general course during the next couple of days as it moves on the southwestern periphery of a mid-level ridge. By the end of the weekend, when Teddy will likely be approaching Bermuda, a turn to the north or north-northeast is forecast to occur as a mid- to upper-level trough moves off the northeastern U.S. coast. Early next week, the trough is expected to cut off, causing Teddy to turn slightly to the left and approach Nova Scotia in 4 to 5 days. The models continue to be in good agreement on this scenario, and only small adjustments were made to the previous forecast track. Teddy will likely fluctuate in intensity over the next day or so while it remains in favorable conditions of low wind shear, warm waters, and a fairly moist air mass. By late this weekend, the hurricane is forecast to traverse over cooler waters churned up by Paulette last week. This should cause a weakening trend to begin. By Monday night, vertical wind shear is expected to drastically increase ahead of the approaching mid-latitude trough. This should not only weaken Teddy, but begin its transition to a large extratropical cyclone, and that transition should be completed before the end of the forecast period. The latest NHC intensity forecast is near the HFIP corrected consensus aid HCCA through 36 h, and then trends toward the SHIPS and LGEM intensity guidance thereafter. Teddy is producing a large area of high seas. The latest maximum seas estimated by TAFB near the core of the hurricane are near 45 feet. Swells from Teddy are spreading far from the center, see Key Messages below. Key Messages: 1. Teddy is expected to approach Bermuda as a hurricane this weekend and make its closest approach to the island late Sunday or Monday. While the exact details of Teddy's track and intensity near the island are not yet known, there is a risk strong winds, storm surge, and heavy rainfall on Bermuda, and watches may be issued later today or tonight. 2. Large swells produced by Teddy are expected to affect portions of the Leeward Islands, the Greater Antilles, the Bahamas, Bermuda, and the southeastern United States during the next few days. These swells could cause life-threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 22.1N 56.1W 115 KT 130 MPH 12H 19/0000Z 23.3N 57.2W 115 KT 130 MPH 24H 19/1200Z 25.2N 58.9W 115 KT 130 MPH 36H 20/0000Z 27.1N 60.7W 110 KT 125 MPH 48H 20/1200Z 28.7N 62.2W 105 KT 120 MPH 60H 21/0000Z 30.7N 62.7W 100 KT 115 MPH 72H 21/1200Z 33.7N 62.2W 95 KT 110 MPH 96H 22/1200Z 41.4N 62.5W 80 KT 90 MPH 120H 23/1200Z 46.8N 62.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Latto

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Tropical Depression Twenty-Two Forecast Discussion Number 4

2020-09-18 16:49:10| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Fri Sep 18 2020 000 WTNT42 KNHC 181449 TCDAT2 Tropical Depression Twenty-Two Discussion Number 4 NWS National Hurricane Center Miami FL AL222020 1000 AM CDT Fri Sep 18 2020 Satellite imagery indicates that Tropical Depression Twenty-Two is getting better organized, with gradually increasing convective banding in the northeastern semicircle. Satellite intensity estimates include 35 kt from TAFB, 30 kt from SAB, and 35 kt from CIMSS satellite consensus, which means the depression is close to tropical-storm strength. Given the lack of organization seen in earlier scatterometer data, the intensity will be held at 30 kt pending the data from the next set of scatterometer overpasses. It should be noted that the Air Force Reserve Hurricane Hunter aircraft that was scheduled to investigate the depression had to turn back after getting hit by lightning. The initial motion is a somewhat uncertain 015/6. For the next 24 h or so, the cyclone should move north-northeastward as it is steered by a mid- to upper-level trough over Texas and northeastern Mexico. This trough is then expected to lift out to the northeast, with low- to mid-level ridging building to the north of the cyclone. This should cause a westward turn at a continued slow forward speed. Near the end of the forecast period, a mid-latitude trough over the central United States should cause the ridge to weaken and steer the cyclone northward to northeastward near the Texas coast. While the guidance agrees with this general sense of the motion, there are a lot of differences in the models on the when's and where's of the various turns. Therefore, it is critical that users not focus on the exact forecast track, especially at days 4 and 5 when the average NHC forecast error is about 175 and 200 miles, respectively. The depression is currently in an environment of light to moderate southwesterly shear, and the global models suggest that this will generally continue through the forecast period. This, combined with forecast dry air entrainment near the 72 h point, has resulted in the intensity guidance keeping the system near to below hurricane strength through the forecast period. The new intensity forecast is changed little from the previous one and calls for the cyclone to be at hurricane strength at 60 and 72 h. However, this part of the forecast lies at the upper edge of the intensity guidance envelope. Key Messages: 1. Tropical Depression Twenty-Two is expected to strengthen to a tropical storm, and possibly a hurricane, while moving slowly over the western Gulf of Mexico during the next few days. 2. There is an increasing risk of heavy rainfall and flooding along the Texas coast from Sunday through at least the middle of next week as the system is forecast to move slowly near the Texas coast. For additional information, see products from your local National Weather Service office. 3. While it is too early to determine what areas could see direct wind and storm surge impacts from this system, interests throughout the western Gulf of Mexico should monitor the progress of this system and future updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 23.8N 93.9W 30 KT 35 MPH 12H 19/0000Z 24.8N 93.6W 35 KT 40 MPH 24H 19/1200Z 25.9N 93.4W 45 KT 50 MPH 36H 20/0000Z 26.3N 93.8W 50 KT 60 MPH 48H 20/1200Z 26.5N 94.6W 60 KT 70 MPH 60H 21/0000Z 26.6N 95.6W 65 KT 75 MPH 72H 21/1200Z 26.9N 96.2W 65 KT 75 MPH 96H 22/1200Z 27.5N 96.5W 60 KT 70 MPH 120H 23/1200Z 28.5N 95.5W 55 KT 65 MPH $$ Forecaster Beven

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Tropical Storm Wilfred Forecast Discussion Number 1

2020-09-18 16:35:11| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Fri Sep 18 2020 000 WTNT43 KNHC 181435 TCDAT3 Tropical Storm Wilfred Discussion Number 1 NWS National Hurricane Center Miami FL AL232020 1100 AM AST Fri Sep 18 2020 Satellite images indicate that the broad area of low pressure over the eastern Atlantic has become better-defined this morning. In addition, scatterometer data also show a closed circulation, albeit with some rain contamination causing some noise near the center. The initial wind speed is set to 35 kt, in accordance with scatterometer data from last night (this morning's data missed the eastern side of the storm). Thus Wilfred has formed, continuing the record-setting pace of the 2020 hurricane season since it is the earliest 21st named storm on record, about 3 weeks earlier than Vince of 2005. Further intensification is possible during the next day or two before a large upper-level trough is forecast to drop into the path of the storm and stay there for at least a few days. That should promote weakening due to a substantial increase in shear, and most of the global models show this tropical cyclone opening up into a trough by day 5. The official forecast follows this scenario, and the NHC intensity forecast is a blend of the consensus and corrected-consensus aids. Wilfred is moving west-northwestward at about 15 kt. The storm is forecast to continue this motion for the next several days, owing to steering from the low- to middle-level subtropical ridge. The guidance is in fair agreement, and the official forecast is near or west of the consensus at all times, leaning in the direction of the HCCA corrected-consensus. I should mention that if Wilfred intensifies more than expected, it would probably move a bit right of the forecast track for a while due to the expected southwesterly flow at higher levels, before eventually turning back west-northwestward. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 11.9N 32.4W 35 KT 40 MPH 12H 19/0000Z 12.6N 34.6W 40 KT 45 MPH 24H 19/1200Z 13.5N 37.5W 40 KT 45 MPH 36H 20/0000Z 14.5N 40.2W 40 KT 45 MPH 48H 20/1200Z 15.6N 42.8W 35 KT 40 MPH 60H 21/0000Z 16.7N 45.5W 30 KT 35 MPH 72H 21/1200Z 17.3N 47.5W 30 KT 35 MPH 96H 22/1200Z 18.0N 50.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 23/1200Z...DISSIPATED $$ Forecaster Blake

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Tropical Depression Twenty-Two Forecast Discussion Number 3

2020-09-18 10:39:30| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Fri Sep 18 2020 000 WTNT42 KNHC 180839 TCDAT2 Tropical Depression Twenty-Two Discussion Number 3 NWS National Hurricane Center Miami FL AL222020 400 AM CDT Fri Sep 18 2020 The depression is still not very well organized. It's surface wind circulation appears to be elongated from southwest to northeast and deep convection is mostly limited to the northeast quadrant of the cyclone. Overnight ASCAT data and the latest TAFB Dvorak estimate both support an intensity of 30 kt. An Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate the system later this morning and should provide more information about the structure of the cyclone. Confidence in the details of the track forecast remain low at this time. Due to the slow forward speed of the cyclone expected into next week, small fluctuations in the depression's heading or speed could have very large implications on any hazards experienced along the Mexico or Texas coasts. It is critical that users not focus on the exact forecast track, especially at days 4 and 5 when the average NHC forecast error is about 175 and 200 miles, respectively. My long-term motion estimate is 025/5 kt, but in reality the depression's movement has been unsteady since it formed yesterday. There is still good general agreement that the system will move slowly north-northeastward for about 36 h, and then turn westward as a ridge builds over the southeast United States. The cyclone will then likely inch closer to the northern Mexico or southern Texas coasts. The details of this evolution vary greatly from model to model and the track guidance spread is higher than usual. The most certain aspect of the forecast is that the depression will not be moving anywhere very quickly well into next week. Although the depression is located within an environment supportive of intensification, only slow strengthening is likely until it gets better organized. Beyond 72 h, the cyclone will begin to interact with a cold front and the drier, more stable air behind it. This should at the very least end any intensification and could lead to weakening. Interaction with land could also cause the system to weaken. The latest statistical intensity guidance is less aggressive, but those models still show the system becoming a hurricane within a couple of days, while the dynamical hurricane models (HWRF, HMON, COAMPS-TC) do not strengthen it quite that much. For now the NHC intensity forecast is largely unchanged and is at the top end of the guidance envelope. Key Messages: 1. Tropical Depression Twenty-Two is expected to strengthen to a tropical storm, and possibly a hurricane, while moving slowly over the western Gulf of Mexico during the next few days. 2. While it is too early to determine what areas could see direct wind, storm surge, and rainfall impacts from this system, interests throughout the western Gulf of Mexico should monitor the progress of this system and future updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 22.9N 94.1W 30 KT 35 MPH 12H 18/1800Z 23.7N 93.7W 35 KT 40 MPH 24H 19/0600Z 24.9N 93.2W 45 KT 50 MPH 36H 19/1800Z 25.7N 93.2W 50 KT 60 MPH 48H 20/0600Z 25.9N 93.8W 60 KT 70 MPH 60H 20/1800Z 26.0N 94.6W 65 KT 75 MPH 72H 21/0600Z 26.3N 95.6W 65 KT 75 MPH 96H 22/0600Z 26.7N 96.3W 60 KT 70 MPH 120H 23/0600Z 27.5N 96.0W 55 KT 65 MPH $$ Forecaster Zelinsky

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