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Tropical Storm Lowell Forecast Discussion Number 5

2020-09-21 22:51:51| Tropical Depression LIDIA

Issued at 300 PM MDT Mon Sep 21 2020

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Tropical Storm Beta Forecast Discussion Number 17

2020-09-21 22:42:53| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Mon Sep 21 2020 000 WTNT42 KNHC 212042 TCDAT2 Tropical Storm Beta Discussion Number 17 NWS National Hurricane Center Miami FL AL222020 400 PM CDT Mon Sep 21 2020 Beta's convective cloud structure has continued to erode since the previous advisory as cold-air stratocumulus clouds have wrapped around the entire and into the system center. Most of the cloud tops are barely reaching the freezing level, with the exception of a small convective burst that has recently developed near and to the northwest of the low-level center. The initial intensity has been lowered to 40 kt and is based on data from the last Air Force Reserve reconnaissance leg that indicated peak SFMR surface winds of 40-42 kt northwest of the center and a dropsonde-measured central pressure of 999-1000 mb. The initial motion estimate 310/04 kt. Beta is expected to move onshore the central Texas coast later tonight, and then stalling along or just inland from the coast during the 12-24 hour period when the steering currents collapse due to a complete break down of a weak ridge over the Gulf of Mexico. A weak trough to the west of the cyclone is then forecast to nudge Beta east-northeastward toward the Gulf of Mexico in the 36-60 hour period, with the cyclone possibly reaching the warm Gulf waters by 48 hours. By 72 hours and beyond, the approaching mid-level trough Beta is expected to move Beta a little faster toward the northeast until the cyclone dissipates over the Lower Mississippi Valley area by day 5. The latest NHC track guidance has shifted a little farther to right or east of the previous forecast track, with most of the models now taking Beta back out over the western Gulf of Mexico by 24 hours. As a result, the new NHC official track forecast has been nudged a little farther to the right of the previous, but remains to the left or west of the NOAA-HCCA consensus model and the UKMET model. West-southwesterly wind shear of 15-20 kt is expected to affect Beta for the next 36 hours or so, followed by a gradual increase in the shear thereafter. That unfavorable flow regime, along with land interaction, should induce a slow weakening trend throughout the forecast period. The NHC intensity forecast remains a little above the available model guidance through 48 hours since Beta is forecast to remain very close to or over the Gulf of Mexico where convective rain bands containing tropical-storm-force winds could possibly move onshore the central and upper Texas coastal areas. Key Messages: 1. The expected slow motion of Beta will produce a long duration rainfall event from the middle Texas coast to southeast Louisiana. Flash, urban, and minor river flooding is likely. Rainfall will also spread northward into the ArkLaTex region and east into the Lower Mississippi Valley and portions of the Southeast through the end of the week. Flash, urban, and isolated minor river flooding is possible. 2. There is the danger of life-threatening storm surge near times of high tide through Tuesday along portions of the Texas and Louisiana coasts within the storm surge warning areas. Residents in these areas should follow advice given by local officials. 3. Tropical-storm-force winds will spread westward across the Texas coast later this evening and continue into Tuesday. FORECAST POSITIONS AND MAX WINDS INIT 21/2100Z 28.2N 96.1W 40 KT 45 MPH 12H 22/0600Z 28.5N 96.6W 35 KT 40 MPH...INLAND 24H 22/1800Z 28.7N 96.5W 35 KT 40 MPH...INLAND 36H 23/0600Z 28.9N 95.8W 35 KT 40 MPH...NEAR TEXAS COAST 48H 23/1800Z 29.2N 94.7W 30 KT 35 MPH...OVER WATER 60H 24/0600Z 29.7N 93.3W 25 KT 30 MPH...OVER WATER 72H 24/1800Z 30.8N 91.6W 20 KT 25 MPH...INLAND 96H 25/1800Z 34.1N 88.7W 20 KT 25 MPH...POST-TROP/INLAND 120H 26/1800Z...DISSIPATED INLAND $$ Forecaster Stewart

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Hurricane Teddy Forecast Discussion Number 37

2020-09-21 16:54:45| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Mon Sep 21 2020 000 WTNT45 KNHC 211454 TCDAT5 Hurricane Teddy Discussion Number 37 NWS National Hurricane Center Miami FL AL202020 1100 AM AST Mon Sep 21 2020 Teddy has weakened some since yesterday. While the maximum 700-mb winds from the latest Air Force Reserve Hurricane Hunter aircraft mission were 93 kt, the peak SFMR values were only 68 kt. A blend of these data with some undersampling due to the large size of Teddy gives an initial wind speed of 80 kt. The hurricane is beginning to accelerate to the north-northeast as the long-awaited mid-latitude trough begins to pick up the cyclone. All of the guidance is in very good agreement that Teddy will benefit from this interaction, growing in both size and maximum winds due to this trough and warmer waters in the Gulf Stream. Thus, the hurricane should intensify overnight, and the new intensity forecast is close to the latest GFS model. Afterward, the baroclinic energy source is exhausted, and Teddy should move north of the Gulf Stream by Wednesday, helping to complete its post-tropical transition. The cyclone should weaken while it accelerates to the north-northeast across eastern Nova Scotia, the Gulf of St. Lawrence, and Newfoundland before dissipating in 3-4 days. No significant changes were made to the track forecast. Teddy's size will likely increase substantially during the next couple of days as it moves northward and interacts with the aforementioned frontal system. Gale force winds are likely along portions of the near shore waters of the northeast U.S. Please see products from your local office for more information about marine hazards. Key Messages: 1. The center of Teddy is forecast to move east of Bermuda today. Wind gusts of tropical-storm-force have been reported on the island, and tropical storm conditions could continue today. 2. Teddy is expected to transition to a powerful post-tropical cyclone as it moves near or over portions of Atlantic Canada late Tuesday through Thursday, where there is an increasing risk of direct impacts from wind, rain, and storm surge. A Tropical Storm Watch is in effect for portions of Nova Scotia, and heavy rainfall across Atlantic Canada is expected with Teddy between Tuesday and Thursday after it becomes a strong post-tropical cyclone. 3. Large swells produced by Teddy are expected to affect portions of Bermuda, the Leeward Islands, the Greater Antilles, the Bahamas, the east coast of the United States, and Atlantic Canada during the next few days. These swells will likely cause life-threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 21/1500Z 31.1N 62.7W 80 KT 90 MPH 12H 22/0000Z 34.4N 62.4W 85 KT 100 MPH 24H 22/1200Z 38.2N 63.7W 90 KT 105 MPH 36H 23/0000Z 40.7N 64.3W 80 KT 90 MPH 48H 23/1200Z 43.7N 63.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 60H 24/0000Z 47.5N 60.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 72H 24/1200Z 51.5N 55.5W 45 KT 50 MPH...POST-TROP/INLAND 96H 25/1200Z...DISSIPATED $$ Forecaster Blake

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Tropical Storm Beta Forecast Discussion Number 16

2020-09-21 16:51:43| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Mon Sep 21 2020 000 WTNT42 KNHC 211451 TCDAT2 Tropical Storm Beta Discussion Number 16 NWS National Hurricane Center Miami FL AL222020 1000 AM CDT Mon Sep 21 2020 There has been little change in Beta's overall convective structure and intensity, with thunderstorm activity pulsing near the center while the outer rain bands have changed little and keep rotating onshore the central and upper Texas coastal areas. Dry air intrusions into the inner-core region have continued to prevent Beta from strengthening by eroding the central dense overcast (CDO). The initial intensity of 45 kt is based on data from an Air Force Reserve reconnaissance aircraft showing peak SFMR surface winds of 40-45 kt and maximum flight-level winds of 50 kt so far, along with a dropsonde-measured central pressure of 996-997 mb. Beta now appears to be moving west-northwestward at a slightly faster forward speed, with the initial motion estimated to be 290/06 kt based on data from the aircraft and NOAA Doppler radars from Corpus Christi and Houston, Texas. The forecast discussion is the same old song as it was 24 hours ago with Beta expected to move just inland over the central Texas coastal Plain in about 12-18 hours, followed by a sharp decrease in motion, possibly resulting in Beta stalling for a few hours as steering currents collapse. A trough to the west combines with a broad ridge to the east located over the Gulf of Mexico to begin nudging Beta slowly northeastward or east-northeastward in 24-36 hours, followed by a slightly faster forward speed on days 3 and 4, which will continue until the cyclone dissipates over Mississippi by day 5. The new NHC track forecast is essentially just an update of the previous advisory track, keeping Beta just inland or near the Texas coast through 60 hours, a scenario that is close to the various consensus models, and which lies between the more westward-and-inland ECMWF solution and the more eastward-and-overwater GFS track forecast. West-southwesterly vertical wind shear of 15-20 kt is not only expected to keep Beta's track close to the coastline, but it will also affect the cyclone's intensity along with land interaction. The closer the cyclone stays near the Gulf of Mexico, the more likely that bands of convection containing tropical-storm-force winds will continue to roll onshore the Texas coast through 36-48 hours. Given that the models over the past 24 hours have been trending toward a track closer to the coast, the NHC official intensity remains unchanged from the previous advisory, and lies a little above all of the available guidance through 48 hours. Key Messages: 1. The expected slow motion of Beta will produce a long duration rainfall event from the middle Texas coast to southeast Louisiana. Flash, urban, and minor river flooding is likely. Rainfall will also spread northward into the ArkLaTex region and east into the Lower Mississippi Valley and portions of the Southeast through the end of the week. Flash, urban, and isolated minor river flooding is possible. 2. There is the danger of life-threatening storm surge near times of high tide through Tuesday along portions of the Texas and Louisiana coasts within the storm surge warning areas. Residents in these areas should follow advice given by local officials. 3. Tropical-storm-force winds will spread westward across the Texas coast later this morning and continue into Tuesday. FORECAST POSITIONS AND MAX WINDS INIT 21/1500Z 27.9N 95.7W 45 KT 50 MPH 12H 22/0000Z 28.3N 96.5W 45 KT 50 MPH...NEAR TEXAS COAST 24H 22/1200Z 28.5N 96.7W 40 KT 45 MPH...INLAND 36H 23/0000Z 28.8N 96.3W 35 KT 40 MPH...INLAND 48H 23/1200Z 29.1N 95.3W 30 KT 35 MPH...NEAR TEXAS COAST 60H 24/0000Z 29.7N 94.0W 25 KT 30 MPH...NEAR TEXAS COAST 72H 24/1200Z 30.8N 92.5W 25 KT 30 MPH...INLAND 96H 25/1200Z 33.5N 89.8W 20 KT 25 MPH...POST-TROP/INLAND 120H 26/1200Z...DISSIPATED INLAND $$ Forecaster Stewart

Tags: number discussion beta storm

 

Tropical Depression Seventeen-E Forecast Discussion Number 4

2020-09-21 16:42:18| Tropical Depression LIDIA

Issued at 900 AM MDT Mon Sep 21 2020

Tags: number discussion tropical depression

 

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