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Tropical Depression Wilfred Forecast Discussion Number 10
2020-09-20 22:33:37| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sun Sep 20 2020 000 WTNT43 KNHC 202033 TCDAT3 Tropical Depression Wilfred Discussion Number 10 NWS National Hurricane Center Miami FL AL232020 500 PM AST Sun Sep 20 2020 Wilfred is not a healthy tropical cyclone as strong vertical shear from the combination of outflow from Hurricane Teddy as well as winds on the southern side of a nearby upper-level trough are impinging upon the system. While there is substantial deep convection, it is more linear rather than curved in appearance and it may be more a product of forcing from the upper-level trough rather than the tropical cyclone itself. Dvorak classifications from SAB and TAFB have reduced some at 18Z, though the intensity remains a perhaps generous 30 kt. The tropical cyclone continues to move west-northwest at a fast 17 kt clip. As the system slowly winds down, it will be increasingly steered by the low-level flow indicating a slower movement toward the west or west-northwest until dissipation. The new track forecast is similar to that from the previous advisory, except for the final 60 hr point that does show a turn toward the northwest based upon the TVCN and HCCA track consensus techniques. Strong shear and dry mid-level humidities should continue to cause a reduction in the deep convection and lead to the system becoming a remnant low in a day or two followed shortly thereafter by dissipation. Most statistical and dynamical intensity guidance is in agreement. A plausible alternate scenario is that the small circulation opens up into a trough and dissipation occurs sooner than indicated below. It is worth noting that the ECMWF model does suggest the possibility of reformation of the system farther north by day three. However, this scenario is discounted at this time. FORECAST POSITIONS AND MAX WINDS INIT 20/2100Z 15.9N 45.8W 30 KT 35 MPH 12H 21/0600Z 16.3N 48.0W 30 KT 35 MPH 24H 21/1800Z 16.5N 49.9W 25 KT 30 MPH 36H 22/0600Z 16.5N 50.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 22/1800Z 16.8N 51.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 23/0600Z 17.8N 52.7W 20 KT 25 MPH...DISSIPATED 72H 23/1800Z...DISSIPATED $$ Forecaster Landsea
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Tropical Storm Beta Forecast Discussion Number 12
2020-09-20 16:59:30| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Sun Sep 20 2020 000 WTNT42 KNHC 201459 TCDAT2 Tropical Storm Beta Discussion Number 12 NWS National Hurricane Center Miami FL AL222020 1000 AM CDT Sun Sep 20 2020 Beta remains a sheared tropical cyclone whose internal structure and convective pattern remained unchanged from the previous advisory, and essentially unchanged over the past 24 hours. The cyclone is going through another bursting phase with the strongest convection displaced into the northeastern quadrant. An Air Force Reserve reconnaissance aircraft investigating Beta this morning has found maximum 850-mb flight-level winds of 61 kt in some rather vigorous thunderstorms in the north of the center, along with believable SFMR surface winds of 45-47 kt in the northeastern quadrant where 45-kt winds were reported by ship KGSG at 0800 UTC. The aircraft also found that the central pressure was down a little bit to 996 mb. Based on these data, the initial intensity is being maintained at 50 kt. It should be noted that the wind field is quite asymmetric with the strongest winds located in the deep convection and farther to the northeast behind an old frontal boundary. Beta remains trapped in weak steering currents and the initial motion is still quite slow at 300/03 kt. Beta is forecast to remain embedded in weak steering currents for the next 48 h or so, caught between a mid-level ridge located over Florida and another ridge situated over the U.S. Southern Plains. Thereafter, the ridge over the Southern Plains if expected to break down while the ridge over Florida amplifies northward and westward across the southern U.S., resulting in a very gradual increase in forward speed toward the north by late Tuesday and then toward the northeast on Wednesday. Beta is forecast to degenerate into a remnant low pressure system by early Wednesday and dissipate inland over the lower Mississippi by late Friday or Saturday. Due to the continued southwest to westerly shear expected to affect Beta, which will keep the convection confined to the northeastern and eastern quadrants, the official forecast track is located along the eastern or right side of the track guidance envelope, and is the right of all of the consensus aids, toward the middle-to-upper Texas coast. Beta is expected to remain under the influence of 15-20 kt of deep layer vertical wind shear, which is enough to keep the cyclone from strengthening much, if any, but not enough to weaken or dissipate the cyclone before it makes landfall. As a result, the intensity is forecast to remain steady at 50 kt until landfall, followed by slower-than-normal weakening for an inland tropical cyclone due to its expected proximity to the Gulf where onshore rainbands could brings higher squalls along the coast. By 72 h, Beta is forecast to weaken fairly quickly into a remnant low since the system will be much farther inland by that time. The intensity model guidance remain in decent agreement, so the new NHC intensity forecast is identical to the previous advisory and is similar to the HCCA consensus model. Key Messages: 1. The expected slow motion of Beta will produce a long duration rainfall event from the middle Texas coast to southern Louisiana. Flash, urban, and river flooding is likely. Rainfall will then spread northward into the lower Mississippi River Valley by mid-week where flash, urban, and 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 are occurring along portions of the northwestern Gulf Coast within the tropical storm warning area in Louisiana. These winds will spread westward to the Texas coast later today and Monday. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 27.2N 93.0W 50 KT 60 MPH 12H 21/0000Z 27.6N 93.9W 50 KT 60 MPH 24H 21/1200Z 28.1N 95.0W 50 KT 60 MPH 36H 22/0000Z 28.6N 95.8W 50 KT 60 MPH 48H 22/1200Z 29.0N 96.0W 45 KT 50 MPH...INLAND 60H 23/0000Z 29.6N 95.7W 40 KT 45 MPH...INLAND 72H 23/1200Z 30.2N 94.7W 30 KT 35 MPH...INLAND 96H 24/1200Z 32.1N 92.1W 20 KT 25 MPH...POST-TROP/INLAND 120H 25/1200Z 34.4N 89.4W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Stewart
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Hurricane Teddy Forecast Discussion Number 33
2020-09-20 16:55:58| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sun Sep 20 2020 000 WTNT45 KNHC 201455 TCDAT5 Hurricane Teddy Discussion Number 33 NWS National Hurricane Center Miami FL AL202020 1100 AM AST Sun Sep 20 2020 The satellite signature of Teddy has degraded from an eye pattern overnight into a central dense overcast this morning. Air Force Reserve Hurricane Hunter aircraft data indicate that the hurricane has weakened, and the initial wind speed is set to 90 kt, perhaps generously. The aircraft data does still show that Teddy remains a large hurricane, with hurricane-force winds extending outward in the northeastward quadrant to about 70 n mi. While the forecast intensity does not change much over the next couple of days, the hurricane should undergo significant changes during that time. Teddy should not lose any more strength by late today due to favorable positioning with an approaching trough, and the gale-force winds should greatly expand due to this trough interaction. In 2 or 3 days, after the system occludes and becomes post-tropical, the cyclone should weaken because of a loss of extratropical forcing while over the cooler water south of Nova Scotia. Eventually Teddy will probably get absorbed by a larger extratropical low around day 5. Model guidance is fairly tightly packed around the official wind forecast, which leans on the global models given the substantial extratropical contributions, plus or minus 5 kt throughout the forecast period. The hurricane has resumed a northwestward motion or 320/8 kt. Teddy is likely to turn northward today and north-northeastward tomorrow due to the aforementioned trough. By early Tuesday, the cyclone should turn back to the north-northwest as it rotates around the same trough, then turn northeastward early Wednesday ahead of yet another trough moving into from eastern Canada. Although the forecast evolution is complex, model guidance is in remarkably good agreement, and no substantial changes were made to the previous forecast. Regardless of the details, every model has a rather large and strong post-tropical cyclone south of Nova Scotia in about 3 days. Key Messages: 1. The center of Teddy is forecast to move east of Bermuda on Monday. Tropical storm conditions are likely on the island beginning this evening and could continue into Monday evening. 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. 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 20/1500Z 28.3N 62.8W 90 KT 105 MPH 12H 21/0000Z 29.2N 63.4W 85 KT 100 MPH 24H 21/1200Z 31.0N 62.9W 85 KT 100 MPH 36H 22/0000Z 34.8N 62.1W 85 KT 100 MPH 48H 22/1200Z 38.8N 63.0W 85 KT 100 MPH 60H 23/0000Z 41.7N 63.4W 75 KT 85 MPH...POST-TROP/EXTRATROP 72H 23/1200Z 44.5N 62.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 96H 24/1200Z 53.0N 53.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 25/1200Z 60.5N 39.5W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Blake
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Tropical Depression Wilfred Forecast Discussion Number 9
2020-09-20 16:50:28| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sun Sep 20 2020 000 WTNT43 KNHC 201450 TCDAT3 Tropical Depression Wilfred Discussion Number 9 NWS National Hurricane Center Miami FL AL232020 1100 AM AST Sun Sep 20 2020 First-light visible imagery of Wilfred shows a well-defined center south of widespread - but not very well banded - deep convection. The improved positioning this morning allows for a more confident assessment of its movement toward the west-northwest at 17 kt. As the system slowly winds down, it will be increasingly steered by the low-level flow indicating a slower movement toward the west or west-northwest until dissipation. The new track forecast is slightly farther west due to the faster initial motion within 36 hours, then slightly farther east afterward based upon the TVCN track consensus approach. While the ASCAT scatterometer passes this morning missed Wilfred's center, ASCAT-B observed 30 kt peak winds in its northeastern quadrant. This value is used as the initial intensity, consistent with both SAB and TAFB's Dvorak classifications. The combination of outflow from Hurricane Teddy as well as winds on the southern side of an impinging upper-level trough are causing about 20 kt vertical shear from the west-northwest. This shear should increase over the next couple of days as Wilfred gets into closer proximity with the trough. The strong shear and dry mid-level humidities should continue to cause a reduction of the deep convection and lead to the system becoming a remnant low in a couple of days followed within another day or so by dissipation. All statistical and dynamical intensity guidance is in agreement with this scenario. Alternatively, Wilfred could become a remnant low sooner, if the convection ceases later today or Monday. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 15.7N 44.2W 30 KT 35 MPH 12H 21/0000Z 16.2N 46.3W 30 KT 35 MPH 24H 21/1200Z 16.5N 48.4W 25 KT 30 MPH 36H 22/0000Z 16.8N 50.0W 25 KT 30 MPH 48H 22/1200Z 17.0N 51.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 23/0000Z 17.2N 52.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 23/1200Z...DISSIPATED $$ Forecaster Landsea
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Tropical Storm Beta Forecast Discussion Number 11
2020-09-20 10:51:27| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Sun Sep 20 2020 000 WTNT42 KNHC 200851 TCDAT2 Tropical Storm Beta Discussion Number 11 NWS National Hurricane Center Miami FL AL222020 400 AM CDT Sun Sep 20 2020 Beta has generally changed little overnight. The storm remains strongly sheared with deep convection confined to the north and northeast of the low-level center. A combination of flight-level, SFMR, and dropsonde data from the Air Force Hurricane Hunters a few hours ago supports keeping the 50-kt initial intensity. It should be noted that the wind field is quite asymmetric with the strongest winds located in the deep convection and farther to the northeast behind an old frontal boundary. Beta was caught in weak steering currents for nearly a day, but it now seems to be moving. The current initial motion estimate is west-northwestward at 3 kt. A mid-level ridge currently centered over the southwestern U.S. is forecast to slide eastward, which should cause Beta to move a little faster to the west-northwestward later today. This motion should continue for a couple of days, taking the storm to the Texas coast on Monday or Monday night. After Beta moves inland, the ridge is forecast to move away as a shortwave trough approaches from the west. This change in the pattern is expected to cause Beta to slow down, or even stall, on Tuesday and then turn northeastward after that. The NHC track forecast lies near the middle of the guidance envelope, and it is fairly similar to the previous prediction. The tropical storm is currently in an environment of about 20 kt of southwesterly wind shear and a fair amount of dry air, especially on the west side of the circulation. Since the shear is not expected to decrease much while Beta moves into an even drier and more stable air mass, little change in intensity is expected through landfall in 36 to 48 hours. After Beta moves inland, steady weakening is forecast due to a combination of land interaction, dry air, and an increase in southwesterly shear. The models are in fair agreement, and this forecast is largely an update of the previous one. Key Messages: 1. The expected slow motion of Beta will produce a long duration rainfall event from the middle Texas coast to southern Louisiana. Flash, urban, and river flooding is likely. Rainfall will then spread northward into the lower Mississippi River Valley by mid-week where flash, urban, and 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 are occurring along portions of the northwestern Gulf Coast within the tropical storm warning area in Louisiana. These winds will spread westward to the Texas coast later today and Monday. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 27.0N 92.7W 50 KT 60 MPH 12H 20/1800Z 27.2N 93.4W 50 KT 60 MPH 24H 21/0600Z 27.6N 94.6W 50 KT 60 MPH 36H 21/1800Z 28.2N 95.6W 50 KT 60 MPH 48H 22/0600Z 28.8N 96.2W 45 KT 50 MPH...INLAND 60H 22/1800Z 29.2N 96.2W 35 KT 40 MPH...INLAND 72H 23/0600Z 29.7N 95.5W 30 KT 35 MPH...INLAND 96H 24/0600Z 31.4N 92.9W 25 KT 30 MPH...INLAND 120H 25/0600Z 33.8N 90.2W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Cangialosi
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