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Tropical Depression Thirteen Forecast Discussion Number 6
2020-08-21 10:49:15| National Hurricane Center (Atlantic)
Issued at 500 AM AST Fri Aug 21 2020 814 WTNT43 KNHC 210849 TCDAT3 Tropical Depression Thirteen Discussion Number 6 NWS National Hurricane Center Miami FL AL132020 500 AM AST Fri Aug 21 2020 Tropical Depression Thirteen remains very disorganized this morning. The associated convection is elongated from northwest to southeast, and the low-level center is located near the northwestern end of the convective area. Additionally, satellite imagery and model analyses indicate that the mid-level center is located several hundred miles to the southeast of the low-level center. Earlier aircraft and scatterometer data suggested the possibility that the system was an open wave. However, the currently available data is ambiguous on whether the system still has a closed circulation, so it will be maintained as a tropical depression. The initial intensity remains 30 kt. The initial motion is west-northwestward or 285/18 kt. There is little change to the track forecast philosophy through about 96 h. A strong subtropical ridge over the western Atlantic should remain north of the depression during the next few days, steering the cyclone at a fast pace to the west-northwest. After that, the ridge weakens some over the eastern Gulf of Mexico, and Tropical Depression Thirteen may interact with Tropical Depression Fourteen, which is also forecast to be in the Gulf by that time, with the result of these things being a turn toward the northwest or north-northwest. The track guidance has shifted southward since the last advisory, with the UKMET shifting far enough to the south that it takes the system over the Caribbean south of Cuba. The new forecast track is also shifted a bit southward from the previous track. However, it lies to the north of the GFS, the UKMET, and the various consensus models. It also lies north of the ECMWF model from 24-72 h. The intensity forecast remains low confidence. The separation between the low- and mid-level centers, as well as some westerly shear and dry air entrainment, suggests that significant strengthening is unlikely during the next 24 h or so. The dynamical models suggests the centers will become more vertically aligned around 36-48 h and that the shear should diminish. However, the system could be close to Hispaniola during this time, and be near Cuba thereafter, especially if it moves south of the forecast track. The upper-level winds over the Gulf of Mexico should be generally favorable for development if the cyclone doesn't get too close to Tropical Depression Fourteen. The possibilities range from the system degenerating to an open wave as seen in the GFS and ECMWF to a major hurricane as seen in the HWRF. Given the uncertainty, the intensity forecast is unchanged from the previous advisory, and it lies a little below the intensity consensus. Key Messages: 1. Tropical storm conditions are possible across portions of the northern Leeward Islands, the Virgin Islands, Puerto Rico, the southeastern Bahamas, and the Turks and Caicos islands later today through Saturday night, and Tropical Storm Watches have been issued for some of these islands. Heavy rainfall is likely across this area beginning today and could cause mudslides and flash and urban flooding through Sunday. 2. The details of the long-range track and intensity forecasts are more uncertain than usual since the system could move over portions of the Greater Antilles this weekend. However, this system could bring some storm surge, rainfall and wind impacts to portions of Hispaniola, Cuba, the Bahamas, and Florida this weekend and early next week. Interests there should monitor this system's progress and updates to the forecast over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 21/0900Z 17.8N 58.5W 30 KT 35 MPH 12H 21/1800Z 18.1N 60.7W 30 KT 35 MPH 24H 22/0600Z 18.8N 64.0W 35 KT 40 MPH 36H 22/1800Z 19.7N 67.5W 40 KT 45 MPH 48H 23/0600Z 20.6N 71.1W 45 KT 50 MPH 60H 23/1800Z 21.8N 74.9W 50 KT 60 MPH 72H 24/0600Z 23.2N 78.5W 55 KT 65 MPH 96H 25/0600Z 26.5N 84.0W 65 KT 75 MPH 120H 26/0600Z 30.0N 87.0W 65 KT 75 MPH $$ Forecaster Beven
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Tropical Depression Fourteen Forecast Discussion Number 4
2020-08-21 10:44:30| National Hurricane Center (Atlantic)
Issued at 500 AM EDT Fri Aug 21 2020 000 WTNT44 KNHC 210844 TCDAT4 Tropical Depression Fourteen Discussion Number 4 NWS National Hurricane Center Miami FL AL142020 500 AM EDT Fri Aug 21 2020 Recent METOP-A/B ASCAT overpasses and earlier aircraft reconnaissance data indicate that the depression's circulation is not well-defined. In fact, the scatterometer data revealed multiple swirls, particularly, one newly developed circulation near a recent strong burst of deep convection near the coast of Honduras. Highest sustained winds from the scatterometer pass were 25-30 kt. For this advisory, the initial position is an uncertain centroid position of the multiple surface centers and the intensity is held at 30 kt. A 53rd Air Force Reserve reconnaissance flight is scheduled for this morning and will hopefully paint a clearer picture on the depression's location. Deep convection has been increasing during the past few hours, especially in the north portion of the depression, so gradual strengthening is still expected before it makes landfall on the east side of the Yucatan Peninsula in about 48 hours. After that time, some weakening is forecast while the cyclone traverses the peninsula. The system is expected to enter the warm waters of the southern Gulf of Mexico around the 60 hr period and restrengthen through the remainder of the forecast. Global models, however, are indicating increasing south-southwesterly shear as the cyclone enters the northwest portion of the gulf which could prevent it from reaching hurricane strength prior to landfall. For now, the forecast will reflect a low-end hurricane making landfall, similar to the HCCA intensity model. The new intensity forecast is basically an update of the previous advisory and is based on a compromise of the various multi-model consensus aids. The initial motion is estimated to be west-northwestward, or 290/10 kt. The depression is forecast to be steered generally northwestward during the next few days by a western extension of the atlantic subtropical ridge that stretches westward across Florida and into the eastern and central Gulf of Mexico. This general motion should result in landfall over the northeastern Yucatan Peninsula on Saturday, with the system entering the northwestern Gulf by the middle of next week. I think it's worth noting that both the UKMET and the DWD, Germany ICON global models are showing some binary interaction between the depression and Tropical Depression Thirteen around the 96-120 hr period while both systems are situated in the Gulf of Mexico. If this scenario actually occurs, the interaction could delay or slow tropical depression Fourteen's landfall over the northwestern Gulf coast. The NHC forecast track is again adjusted a little to the right of the previous forecast and lies close to the TVCA and HCCA consensus solutions. Key Messages: 1. Tropical Depression Fourteen is expected to strengthen over the northwestern Caribbean Sea through Saturday, and is likely to produce tropical-storm-force winds and heavy rainfall over portions of the coasts of Nicaragua and Honduras, including the Bay Islands, through today. The system is expected be near or at hurricane strength when it reaches the Yucatan Peninsula of Mexico late Saturday where a Hurricane Watch and a Tropical Storm Warning are in effect. 2. The system is expected to move into the south-central Gulf of Mexico as a tropical storm on Sunday. Some strengthening is anticipated while it moves northwestward over the western Gulf of Mexico early next week, but it is too soon to know exactly how strong it will get or the location and magnitude of impacts it will produce along the central or northwestern Gulf Coast. Interests in that area should continue monitoring the progress of this system over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 21/0900Z 15.4N 83.1W 30 KT 35 MPH 12H 21/1800Z 16.3N 84.3W 40 KT 45 MPH 24H 22/0600Z 17.7N 85.4W 50 KT 60 MPH 36H 22/1800Z 19.2N 86.4W 60 KT 70 MPH 48H 23/0600Z 20.7N 87.5W 50 KT 60 MPH...INLAND 60H 23/1800Z 22.5N 88.8W 50 KT 60 MPH...OVER WATER 72H 24/0600Z 24.5N 90.2W 65 KT 75 MPH 96H 25/0600Z 28.1N 93.0W 65 KT 75 MPH 120H 26/0600Z 30.4N 94.6W 45 KT 50 MPH...INLAND $$ Forecaster Roberts
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Tropical Storm Genevieve Forecast Discussion Number 20
2020-08-21 10:40:20| Tropical Depression LIDIA
Issued at 300 AM MDT Fri Aug 21 2020
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Tropical Depression Fourteen Forecast Discussion Number 3
2020-08-21 04:58:15| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Thu Aug 20 2020 000 WTNT44 KNHC 210258 TCDAT4 Tropical Depression Fourteen Discussion Number 3 NWS National Hurricane Center Miami FL AL142020 1100 PM EDT Thu Aug 20 2020 The overall convective pattern has improved somewhat since the previous advisory, with a band of deep convection having developed near and just south of the low-level center. A pronounced mid-level circulation has been rotating westward to the north of the center of the broader low-level circulation, which has likely prevented the cyclone from becoming a tropical storm by now, especially given the very impressive outflow pattern. However, NOAA buoy 42057 to the north of the center recently reported a sustained wind of 29 kt at 4 meters elevation, which equals about a 32-kt 10-meter wind speed, which means that the cyclone isn't far from becoming a tropical storm. The intensity is being maintained at 30 kt until convection becomes more persistent. The center has been reforming a little farther north and has also slowed down, with the initial motion now being west-northwestward or 285/12 kt. The slower and farther north initial position has required a slight northward shift in the forecast track for the next 24 hours and, as a result, the center of the cyclone is no longer expected to make landfall very far inland over Honduras or Nicaragua, if it makes landfall at all. By 36 hours, the new NHC forecast track shifts back closer to the previous advisory track due to a strong mid-level ridge extending westward across Florida and into the eastern and central Gulf of Mexico. That feature is expected to keep the cyclone moving in a general northwestward direction on days 2-5, resulting in landfall over the northeastern Yucatan Peninsula on Saturday, and be approaching the northwestern Gulf coast by the middle of next week. The official forecast track lies along the southern edge of the guidance envelope, close to the middle of the simple consensus models and a little south of the NOAA-HCCA corrected model. Due to the northward shift in the new forecast track, the center and inner-core wind field of the cyclone will not be disrupted as much as previously expected, which has significant implications in the intensity forecast. The depression is now expected to reach hurricane strength just before it makes landfall on the east side of the Yucatan Peninsula in about 48 hours. Weakening is forecast in 60 hours while the cyclone moves across northeastern Yucatan, followed by gradual re-strengthening thereafter. Ocean temperatures along the path of the cyclone are forecast to be 30.0-30.5 deg C and the vertical shear is expected to remain low at less than 10 kt through 96 hours. Those conditions coupled with the impressive outflow pattern should allow for at least typical strengthening. By 120 hours, the GFS- and ECMWF-based SHIPS models show the vertical wind shear increasing sharply from the southwest to 20-25 kt, which would normally induce weakening. However, it appears that those models are incorporating some strong jetstream winds of 60-70 kt well to the northwest of the center of the cyclone, which has resulted in high bias in the shear output. Therefore, the cyclone is forecast to be near hurricane strength when it approaches the Texas coast in 120 hours. The new intensity forecast is similar to but a little higher then the previous advisory due to less land interaction than previously expected, and is is a blend of the Decay-SHIPS and LGEM models, which are at the upper-end of the guidance envelope. Key Messages: 1. Tropical Depression Fourteen is expected to strengthen over the northwestern Caribbean Sea through Saturday, and is likely to produce tropical-storm-force winds and heavy rainfall over portions of the coasts of Nicaragua and Honduras, including the Bay Islands, beginning tonight through Friday. The system is expected be near or at hurricane strength when it reaches the Yucatan Peninsula of Mexico late Saturday where a Hurricane Watch and a Tropical Storm Warning are in effect. 2. The system is expected to move into the south-central Gulf of Mexico as a tropical storm on Sunday. Some strengthening is anticipated while it moves northwestward over the western Gulf of Mexico early next week, but it is too soon to know exactly how strong it will get or the location and magnitude of impacts it will produce along the central or northwestern Gulf Coast. Interests in that area should continue monitoring the progress of this system over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 14.9N 82.2W 30 KT 35 MPH 12H 21/1200Z 15.5N 83.8W 35 KT 40 MPH 24H 22/0000Z 16.8N 85.1W 45 KT 50 MPH 36H 22/1200Z 18.2N 86.0W 55 KT 65 MPH 48H 23/0000Z 19.8N 87.2W 65 KT 75 MPH 60H 23/1200Z 21.4N 88.5W 40 KT 45 MPH...INLAND 72H 24/0000Z 23.2N 89.8W 50 KT 60 MPH...OVER WATER 96H 25/0000Z 26.7N 92.3W 65 KT 75 MPH 120H 26/0000Z 29.1N 94.3W 65 KT 75 MPH $$ Forecaster Stewart
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Tropical Depression Thirteen Forecast Discussion Number 5
2020-08-21 04:49:47| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Thu Aug 20 2020 000 WTNT43 KNHC 210249 TCDAT3 Tropical Depression Thirteen Discussion Number 5 NWS National Hurricane Center Miami FL AL132020 1100 PM AST Thu Aug 20 2020 A NOAA Hurricane Hunter aircraft has been flying all around the circulation of the depression this evening, providing valuable information on the low-level structure. The strongest winds are primarily northeast of the center, with an elongated surface circulation and a mid-level swirl near the southern end. While the plane couldn't locate a definite center, there's enough uncertainty and curvature in the plane's wind field data to hold onto the system as 30-kt tropical depression for now. Another mission should be in the area around 1200 UTC. A late-arriving scatterometer pass confirms both the disorganization of the cyclone and the maximum winds. The initial motion continues about the same as before, 290/19. A strong subtropical ridge over the western Atlantic should remain north of the depression during the next few days, steering the cyclone at a fast pace to the west-northwest. After the weekend, the ridge weakens some over the eastern Gulf of Mexico, leading to depression probably turning more to the northwest. The guidance has trended to the south and west after 24 hours tonight, led by the GFS and HWRF models. I'm not inclined to make significant changes since the models are about to ingest the information from the reconnaissance mission, plus the initial disorganization of the center, but the new track is still adjusted slightly to the south and west, north of much of the guidance. The depression should be moving through mixed conditions over the next few days. While the water is very warm, GFS forecasts show that there is significant mid-level shear that could continue to mix in nearby dry air toward the center. This shear will probably relax late this weekend or early next week, but there is very poor agreement on how much shear remains and the timing of this event. In addition, a track any farther south would result in potentially mountainous land interaction, which also increases the intensity forecast uncertainty. No significant changes were made to the previous wind speed forecast, and the overall confidence in both the track and intensity forecasts remain lower than normal. Key Messages: 1. Tropical storm conditions are possible across portions of the northern Leeward Islands, the Virgin Islands, and Puerto Rico Friday night and Saturday, and Tropical Storm Watches have been issued for some of these islands. Heavy rainfall is likely across this area beginning late Friday and could cause mudslides and flash and urban flooding through Sunday. 2. The details of the long-range track and intensity forecasts are more uncertain than usual since the system could move over portions of the Greater Antilles this weekend. However, this system could bring some storm surge, rainfall and wind impacts to portions of Hispaniola, Cuba, the Bahamas, and Florida this weekend and early next week. Interests there should monitor this system's progress and updates to the forecast over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 17.3N 56.4W 30 KT 35 MPH 12H 21/1200Z 17.9N 59.1W 30 KT 35 MPH 24H 22/0000Z 18.6N 62.4W 35 KT 40 MPH 36H 22/1200Z 19.4N 65.7W 40 KT 45 MPH 48H 23/0000Z 20.3N 69.2W 45 KT 50 MPH 60H 23/1200Z 21.3N 72.8W 50 KT 60 MPH 72H 24/0000Z 22.6N 76.4W 55 KT 65 MPH 96H 25/0000Z 26.0N 82.5W 65 KT 75 MPH 120H 26/0000Z 29.0N 85.5W 65 KT 75 MPH $$ Forecaster Blake
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