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Post-Tropical Cyclone Alpha Forecast Discussion Number 3

2020-09-19 04:36:23| National Hurricane Center (Atlantic)

Issued at 300 AM GMT Sat Sep 19 2020 000 WTNT44 KNHC 190236 TCDAT4 Post-Tropical Cyclone Alpha Discussion Number 3 NWS National Hurricane Center Miami FL AL242020 300 AM GMT Sat Sep 19 2020 METEOSAT imagery, IPMA radar data, and surface observations indicate that Alpha has degenerated to a post-tropical remnant low just a few miles to the southeast of Viseu, Portugal. Therefore, this the last NHC advisory. Surface wind data support an initial intensity of 25 kt. The rapidly deteriorating small remnant low is expected to move generally toward the northeast at about 14 kt for the next 6 to 12 hours before dissipating over northern Spain by Saturday night. The NHC forecast track is basically an update of the previous advisory and lies between the tightly clustered deterministic 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 19/0300Z 40.9N 6.9W 25 KT 30 MPH...POST-TROPICAL 12H 19/1200Z 42.6N 4.4W 20 KT 25 MPH...POST-TROP/INLAND 24H 20/0000Z...DISSIPATED $$ Forecaster Roberts

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Hurricane Teddy Forecast Discussion Number 26

2020-09-18 22:56:47| National Hurricane Center (Atlantic)

Issued at 500 PM AST Fri Sep 18 2020 000 WTNT45 KNHC 182056 TCDAT5 Hurricane Teddy Discussion Number 26 NWS National Hurricane Center Miami FL AL202020 500 PM AST Fri Sep 18 2020 Both NOAA and U.S. Air Force Hurricane Hunter aircraft have been investigating Teddy since this morning. The highest flight level wind measured by the aircraft was 119 kt at 750 mb, which reduces to around 101 kt at the surface. The latest central measured by the aircraft is up 4 mb from the previous advisory, indicating only some slight weakening. Earlier microwave images indicated that an eyewall replacement cycle had been taking place and some drier air had intruded into the southern portion of the circulation, leaving a partial break in the eyewall. This may explain the reason why the aircraft have not been finding winds as strong as they did previously, and in fact found a double wind maxima in the northern portion of the circulation. These eyewall replacement cycles are common in intense tropical cyclones, and oftentimes the systems recover within 12-24 h as long as the environmental conditions support it. Over the past hour or so, the ring of deep convection has appeared less broken and is beginning to expand in size, which could be an indication that the hurricane is recovering from the eyewall replacement. Based on the possibility of some undersampling by the aircraft, the increase of only 4 mb in central pressure, and the latest convective trends, the initial intensity is being lowered only slightly to 110 kt. Teddy continues its long trek northwestward, now at 12 kt. The hurricane 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 about 4 days. The models continue to be in good agreement on this scenario, and only small adjustments were made to the previous forecast track. The environment around Teddy will be conducive for maintaining an intense hurricane for the next 24 h or so, as the ocean temperatures will remain warm with low vertical wind shear and a fairly moist atmosphere. After 24 h, the hurricane is forecast to cross cooler waters churned up by Paulette last week. This should cause a slow weakening trend to begin. By Monday night, vertical wind shear is expected to drastically increase ahead of an 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 around day 4 of the forecast period. The latest NHC intensity forecast is near or a little above HCCA and IVCN through 24 h, and then trends toward the SHIPS 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. While the center of Teddy is forecast to move east of Bermuda late Sunday or Monday, there is still a risk of strong winds, storm surge, and heavy rainfall on the island, and a Tropical Storm Watch is in effect. 2. Teddy is expected to transition to a powerful post-tropical cyclone as it moves near or over portions of Atlantic Canada early next week, where there is an increasing risk of direct impacts from wind, rain, and storm surge. Residents there should closely monitor the progress of Teddy and updates to the forecast through the weekend. 3. Large swells produced by Teddy are expected to affect portions of the Leeward Islands, the Greater Antilles, the Bahamas, Bermuda, the east coast of the United States, and Atlantic Canada during the next few days. These swells could cause life-threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 23.1N 57.0W 110 KT 125 MPH 12H 19/0600Z 24.5N 58.1W 110 KT 125 MPH 24H 19/1800Z 26.5N 59.9W 110 KT 125 MPH 36H 20/0600Z 28.1N 61.6W 105 KT 120 MPH 48H 20/1800Z 29.7N 62.6W 100 KT 115 MPH 60H 21/0600Z 31.8N 62.5W 95 KT 110 MPH 72H 21/1800Z 35.6N 61.7W 85 KT 100 MPH 96H 22/1800Z 43.2N 62.7W 75 KT 85 MPH...POST-TROP/EXTRATROP 120H 23/1800Z 48.5N 59.3W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Latto

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Subtropical Storm Alpha Forecast Discussion Number 2

2020-09-18 22:55:47| National Hurricane Center (Atlantic)

Issued at 900 PM GMT Fri Sep 18 2020 000 WTNT44 KNHC 182055 TCDAT4 Subtropical Storm Alpha Discussion Number 2 NWS National Hurricane Center Miami FL AL242020 900 PM GMT Fri Sep 18 2020 Radar data from Portugal indicated that Alpha made landfall at about 1830 UTC with a fairly impressive spiral band signature. It is estimated that the winds were 45 kt at landfall, and a sustained 10-minute wind of 39 kt was recorded at Sao Pedro de Noel. The minimum central pressure is analyzed at 996 mb at landfall due to a 999 mb value at Monte Real with a 31-kt sustained wind. Since these data were recorded, the radar presentation has deteriorated, and satellite imagery suggests the small cyclone could be de-coupling from its mid-level center. The winds are assumed to have come down, with a current estimate of 40 kt. The small cyclone should continue to move northeastward at about 15 kt for the next 12-24 hours before dissipating over northern Spain or the Bay of Biscay. No significant changes are required to the forecast for track or intensity. 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 18/2100Z 40.4N 8.4W 40 KT 45 MPH...INLAND 12H 19/0600Z 42.1N 6.1W 25 KT 30 MPH...POST-TROP/INLAND 24H 19/1800Z...DISSIPATED $$ Forecaster Blake

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Tropical Storm Beta Forecast Discussion Number 5

2020-09-18 22:53:15| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Fri Sep 18 2020 000 WTNT42 KNHC 182053 TCDAT2 Tropical Storm Beta Discussion Number 5 NWS National Hurricane Center Miami FL AL222020 400 PM CDT Fri Sep 18 2020 Satellite imagery indicates that the circulation of Tropical Depression 22 has become better defined, and most objective and subjective satellite intensity estimates are now 35 kt. Based on this, along with 33 kt 1-mi average winds from NOAA buoy 42002, the depression is upgraded to Tropical Storm Beta with an initial intensity of 35 kt. Although the system is now a tropical storm, satellite imagery shows that the convective pattern is becoming elongated due to the effects of southwesterly vertical wind shear. Visible imagery and scatterometer data showed that the center of Beta was a bit farther east than previously thought, and the initial motion is a somewhat uncertain 025/8. This motion should continue for the next 12-24 h as the storm is steered by a mid- to upper-level trough over Texas and northeastern Mexico. After that time, the trough should weaken and lift out to the northeast, with a mid-level ridge building to the north of the cyclone above an already present low-level ridge. This ridge should act as a Beta blocker, causing the storm to turn westward toward the western Gulf coast. Between 72-120 h, the mid-level ridge weakens as another mid-latitude trough moves through the central United States, and this is expected to cause the storm to slowly recurve toward the northeast. One change in the track guidance since the previous forecast is that the GFS and ECMWF are a bit faster on the westward motion and show the center near the Texas coast in about 72 h. The latter part of the new track forecast also shifts westward, but it is still to the east of the GFS/ECMWF. There is also a chance that Beta could move more northward than forecast before the trough lifts out, which adds an additional touch of uncertainty to the track forecast. So, it is critical that users not focus on the exact forecast track, especially at days 3 to 5. The global models suggest that the current shear may decrease a little after 24 h when the upper-level trough moves away from Beta. However, there is a chance of at least some dry air entrainment that would hamper strengthening. The intensity guidance for the most part continues to forecast Beta to reach a peak intensity below hurricane strength, although the latest SHIPS model forecasts a peak intensity near 65 kt. The new intensity forecast is again unchanged in making Beta a hurricane at 60 and 72 h, and it lies at the upper edge of the intensity guidance. Key Messages: 1. Beta is expected to strengthen and possibly become 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 northwest Gulf Coast Sunday through at least the middle of next week as Beta is forecast to move slowly toward and along or offshore of the coast through that time. 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 Beta, interests throughout the western Gulf of Mexico should monitor the progress of this system and future updates to the forecast. Storm Surge and Tropical Storm or Hurricane watches could be issued tonight or Saturday. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 24.3N 93.1W 35 KT 40 MPH 12H 19/0600Z 25.1N 92.9W 40 KT 45 MPH 24H 19/1800Z 25.9N 93.0W 45 KT 50 MPH 36H 20/0600Z 26.1N 93.7W 50 KT 60 MPH 48H 20/1800Z 26.3N 94.6W 60 KT 70 MPH 60H 21/0600Z 26.5N 95.5W 65 KT 75 MPH 72H 21/1800Z 26.8N 96.3W 65 KT 75 MPH 96H 22/1800Z 27.5N 96.5W 60 KT 70 MPH 120H 23/1800Z 28.5N 96.0W 55 KT 65 MPH $$ Forecaster Beven

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Tropical Storm Wilfred Forecast Discussion Number 2

2020-09-18 22:45:15| National Hurricane Center (Atlantic)

Issued at 500 PM AST Fri Sep 18 2020 000 WTNT43 KNHC 182045 TCDAT3 Tropical Storm Wilfred Discussion Number 2 NWS National Hurricane Center Miami FL AL232020 500 PM AST Fri Sep 18 2020 There haven't been a lot of changes with Wilfred today, with the northern side of the circulation looking rather dry while the center remains close to a burst of convection. The initial wind speed is kept 35 kt, closest to the TAFB classification. Wilfred could strengthen some during the next day or so before increasing upper-level westerlies winds likely begin by Sunday. A gradual weakening is expected into early next week, though the model guidance is in worse agreement than the last advisory due to the positioning of an upper-level low. The forecast continues to show the storm ending up on the convergent side of the low and dissipating, close to the previous one. Wilfred is moving west-northwestward at about 16 kt, after accounting for a re-positioning westward. Most of the guidance agrees on a scenario that maintains this track for the next few days, with a turn toward the west as the cyclones dissipates. The new forecast is closest to the GFS-based guidance. Similar to the intensity forecast, however, there are some models that suggest Wilfred could slow down and turn to the right in a couple of days if it is stronger than anticipated. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 12.5N 34.4W 35 KT 40 MPH 12H 19/0600Z 13.2N 36.7W 40 KT 45 MPH 24H 19/1800Z 14.3N 39.7W 40 KT 45 MPH 36H 20/0600Z 15.4N 42.6W 40 KT 45 MPH 48H 20/1800Z 16.4N 45.4W 35 KT 40 MPH 60H 21/0600Z 17.1N 48.0W 30 KT 35 MPH 72H 21/1800Z 17.5N 50.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 22/1800Z...DISSIPATED $$ Forecaster Blake

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