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Potential Tropical Cyclone Nine Forecast Discussion Number 4
2020-07-29 10:46:56| National Hurricane Center (Atlantic)
Issued at 500 AM AST Wed Jul 29 2020 000 WTNT44 KNHC 290846 TCDAT4 Potential Tropical Cyclone Nine Discussion Number 4 NWS National Hurricane Center Miami FL AL092020 500 AM AST Wed Jul 29 2020 Satellite and surface data indicate that the system remains a trough of low pressure, elongated from SSW to NNE, with almost all of the strong winds far north of the center position. The most significant curvature in the low-level wind field and on radar are near Dominica now, which has good continuity from the previous advisory, so this feature will continue to be used as the center. A combination of unflagged SFMR winds from an Air Force plane and earlier scatterometer winds support 40 kt as the initial wind speed. The initial motion estimate is about the same as before or 295/20 kt. The ridge to the north of the disturbance is forecast to remain strong for the next 36 h, which keeps the system moving speedily in a general west-northwestward direction just south of the Leeward Islands today, and near or over the Greater Antilles on Thursday. The ridge is forecast to weaken after that time, which should cause the cyclone to slow down, and potentially gain more latitude over the southwestern Atlantic. The model guidance is generally showing a narrow ridge persisting for a bit longer, however, causing a small south and west shift in the new NHC forecast at long range. However, it should be emphasized that this forecast track is highly uncertain until a true center forms. Satellite images indicate that a large burst of convection is occuring near the poorly defined center, which will likely lead to the system becoming a tropical storm later today. Further intensification is possible before landfall in the Dominican Republic on Thursday, assuming the structure continues to improve, and the wind speed forecast is adjusted slightly higher in the near term. The cyclone will probably take some time to recover after moving over the very high mountains of Hispaniola, and some of the guidance after that time shows an increase in southwesterly shear over the Straits of Florida that could limit the potential of the cyclone. Simply put, there are a lot of hurdles in the system's way, so it is best to stay on the conservative side at the moment and continue to stress the large uncertainty after it leaves the Caribbean. Little change was made to the forecast intensity, although the guidance has come down at longer range for many of the models. Interests in Hispaniola, the Bahamas, Cuba, and Florida should continue to monitor forecasts as changes to both the track and intensity are likely. Key Messages: 1. Potential Tropical Cyclone Nine will produce heavy rains and potentially life-threatening flash flooding and mudslides across the northern Leeward Islands, the Virgin Islands, Puerto Rico, and the Dominican Republic. 2. Tropical storm conditions are likely across portions of the Leeward Islands, the Virgin Islands and Puerto Rico today and spreading westward to portions of the Dominican Republic and Haiti on Thursday. Tropical Storm Warnings are in effect for these areas. Do not focus on the details of the track forecast, as rainfall and wind hazards will extend far from the center of the system. 3. The details of the long-range track and intensity forecasts are more uncertain than usual since the system does not have a well-defined center and it could move over portions of the Greater Antilles later this week. However, this system could bring some rainfall and wind impacts to portions of Cuba, the Bahamas, and Florida by the end of the week. Interests there should monitor its progress and updates to the forecast over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 15.3N 61.3W 40 KT 45 MPH...POTENTIAL TROP CYCLONE 12H 29/1800Z 16.3N 64.1W 45 KT 50 MPH...TROPICAL STORM 24H 30/0600Z 17.8N 67.6W 50 KT 60 MPH 36H 30/1800Z 19.3N 71.0W 40 KT 45 MPH...INLAND 48H 31/0600Z 20.6N 74.0W 40 KT 45 MPH...OVER WATER 60H 31/1800Z 22.1N 76.7W 45 KT 50 MPH 72H 01/0600Z 23.3N 78.7W 50 KT 60 MPH 96H 02/0600Z 25.5N 81.5W 55 KT 65 MPH 120H 03/0600Z 28.5N 83.0W 45 KT 50 MPH $$ Forecaster Blake
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Potential Tropical Cyclone Nine Forecast Discussion Number 3
2020-07-29 04:53:21| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Tue Jul 28 2020 000 WTNT44 KNHC 290253 TCDAT4 Potential Tropical Cyclone Nine Discussion Number 3 NWS National Hurricane Center Miami FL AL092020 1100 PM AST Tue Jul 28 2020 Earlier wind data from an Air Force reconnaissance aircraft and a recent 0038Z ASCAT-A overpass indicate that the disturbance has not become any better organized since the previous advisory. There were indications of a circulation center located near the position estimate used in this advisory. However, there was a sharp cusp noted in the ASCAT wind field, and that was used for positioning the disturbance since it lies closest to the strong convective band and best upper-level divergence. The initial intensity of 35 kt is based on several ASCAT wind vectors of 35-36 kt located well north of the center. The 35-kt intensity is also consistent with a 0000Z TAFB Dvorak satellite intensity estimate of T2.5/35 kt. The initial motion estimate is an uncertain 295/22 kt. The ridge to the north of the disturbance is forecast to remain strong for the next 36-48 h, which keeps the system moving in a general west-northwestward direction across the Lesser Antilles tonight and Wednesday, and near or over the Greater Antilles Wednesday night and Thursday. For such a loosely organized system at this time, the models are in fairly good agreement on the large disturbance slowing down significantly after 48 h, reaching forward speeds of only 10-12 kt when it reaches the very warm waters of the Straits of Florida in 72-96 h. On days 4 and 5, the system is expected to slow even further and turn northward into a break in the subtropical ridge that is expected to develop across Florida and the Bahamas. The new NHC track forecast is similar to but a little south of the previous advisory track, mainly due to the more westward initial position, and lies along the southern portion of the guidance envelope near the middle of the consensus models. Regardless of the exact track, the system is expected to bring locally heavy rainfall to much of the Lesser Antilles, and tropical-storm-force winds to portions of the Leeward Islands, the Virgin Islands, and Puerto Rico during the next 24 hours. The intensity forecast remains problematic for primarily two reasons: 1) the lack of a well-defined center and inner-core wind field and 2) likely land interaction to some degree. In the short-term, a bonafide center could develop tonight in response to the expected development of intense convection caused by orographic forcing by the mountainous islands of the central and northern Leeward Islands. Once a center closes off, which has likely been inhibited from doing so due to the disturbance's fast forward speed in excess of 20 kt, the low-level convergence will improve and convection will become more organized and symmetrical, allowing for strengthening to occur. The main question is how much land interaction with Puerto Rico and Hispaniola will disrupt the circulation in the 36-48-hour period. Assuming the system remains intact after emerging off the coast of Hispaniola, the slow track over the very warm waters of the Straits of Florida would result in more strengthening, assuming the system doesn't interact with the Cuban landmass. Although the GFS-and ECMWF-based SHIPS intensity guidance shows considerable southwesterly vertical wind shear of 20-30 kt in the 72-96 h period when the disturbance is over the Straits, the global model fields show that this is self-induced shear caused by the SHIPS model incorporating the system's impressive upper-level outflow winds in its shear calculations. As a result, this is not being considered a negative intensity factor compared to land interaction. Due to aforementioned uncertainties, the new NHC intensity forecast remains on the conservative side, and lies between the slightly weaker IVCN and stronger NOAA-HCCA consensus models. Interests in Hispaniola, the Bahamas, Cuba, and Florida should continue to monitor forecasts as changes to both the track and intensity are likely. Key Messages: 1. Potential Tropical Cyclone Nine will produce heavy rains and potentially life-threatening flash flooding and mudslides across the northern Leeward Islands, the Virgin Islands, Puerto Rico, and the Dominican Republic. 2. Tropical storm conditions are likely across portions of the Leeward Islands, the Virgin Islands, Puerto Rico, and portions of the Dominican Republic beginning Wednesday and spreading westward through Thursday. Tropical Storm Warnings are in effect for these areas. Do not focus on the details of the track forecast, as rainfall and wind hazards will extend far from the center of the system. 3. The details of the long-range track and intensity forecasts are more uncertain than usual since the system does not have a well-defined center and it could move over portions of the Greater Antilles later this week. However, this system could bring some rainfall and wind impacts to portions of Hispaniola, Cuba, the Bahamas, and Florida by the end of the week. Interests there should monitor its progress and updates to the forecast over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 14.6N 59.4W 35 KT 40 MPH...POTENTIAL TROP CYCLONE 12H 29/1200Z 15.7N 62.3W 40 KT 45 MPH 24H 30/0000Z 17.4N 65.9W 45 KT 50 MPH 36H 30/1200Z 18.7N 69.3W 45 KT 50 MPH...INLAND 48H 31/0000Z 20.1N 72.6W 45 KT 50 MPH...OVER WATER 60H 31/1200Z 21.5N 75.5W 50 KT 60 MPH 72H 01/0000Z 22.8N 77.7W 55 KT 65 MPH 96H 02/0000Z 25.7N 80.7W 55 KT 65 MPH...INLAND 120H 03/0000Z 27.9N 82.0W 45 KT 50 MPH...INLAND $$ Forecaster Stewart
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Potential Tropical Cyclone Nine Forecast Discussion Number 2
2020-07-28 22:40:20| National Hurricane Center (Atlantic)
Issued at 500 PM AST Tue Jul 28 2020 000 WTNT44 KNHC 282040 TCDAT4 Potential Tropical Cyclone Nine Discussion Number 2 NWS National Hurricane Center Miami FL AL092020 500 PM AST Tue Jul 28 2020 The overall structure of the disturbance has not changed much since this morning. New clusters of convection have developed over the northern portion of the elongated circulation and the Air Force Reserve reconnaissance aircraft has been unable to find a well-defined center. The aircraft measured some SFMR winds of 30-35 kt well to the northwest of the trough axis, and these data along with the earlier ASCAT form the basis of the 35 kt initial intensity. The lastest dynamical model guidance still suggests that the system will consolidate over the next 12-18 hours and the disturbance is expected to become a tropical storm before it reaches the Leeward Islands on Wednesday. The particulars of the track forecast remain uncertain since the system lacks a well-defined center. The initial motion estimate is a highly uncertain 285/20 kt. The overall track foreast reasoning remains the same, with the disturbance expected to move west-northwestward over the next several days to the south of a subtropical ridge that extends westward over the western Atlantic. The 12Z track guidance is in agreement on the overall scenario, but some differences are noted due primarily to the system's strength and vertical depth. Models such as the UKMET and HWRF, which depict a stronger cyclone, are along the northern side of the guidance envelope, while the weaker solutions remain more equatorward. The updated NHC track forecast is similar to the previous advisory and lies a little south of the various consensus aids. Regardless of the exact track, the system is expected to bring locally heavy rainfall to much of the Lesser Antilles, and tropical-storm-force winds to portions of the Leeward Islands, the Virgin Islands, and Puerto Rico within the next 24-36 hours. The global model guidance suggests that the system will consolidate overnight and should acquire a better defined center. As this occurs, the disturbance is likely to gradually strengthen within the low vertical wind shear environment that it is situated in. Between 36 and 72 hours, the strength of the system will largely be dependent on the amount of land it encounters. If the system moves over the Greater Antilles it is likely to be weaker than indicated in the official forecast, but a path north or south of Hispaniola could result in a stronger system. Later in the period, some southwesterly shear could also temper further strengthening. The GFS and ECMWF models generally weaken the system in the longer range due to these negative factors. The NHC intensity forecast is unchanged from the previous advisory, but an usually high degree of uncertainty regarding the future track and intensity of the system remains. Interests in Hispaniola, the Bahamas, Cuba, and Florida should continue to monitor forecasts as changes to both track and intensity are likely. Key Messages: 1. Potential Tropical Cyclone Nine will produce heavy rains and potentially life-threatening flash flooding and mudslides across the northern Leeward Islands, the Virgin Islands, Puerto Rico, and the Dominican Republic. 2. Tropical storm conditions are likely across portions of the Leeward Islands, the Virgin Islands, Puerto Rico, and portions of the Dominican Republic beginning Wednesday and spreading westward through Thursday. Tropical Storm Warnings are in effect for these areas. Do not focus on the details of the track forecast, as rainfall and wind hazards will extend far from the center of the system. 3. The details of the long-range track and intensity forecasts are more uncertain than usual since the system does not have a well-defined center and it could move over portions of the Greater Antilles later this week. However, this system could bring some rainfall and wind impacts to portions of Hispaniola, Cuba, the Bahamas, and Florida by the end of the week. Interests there should monitor its progress and updates to the forecast over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 14.4N 55.9W 35 KT 40 MPH...POTENTIAL TROP CYCLONE 12H 29/0600Z 15.4N 58.8W 35 KT 40 MPH 24H 29/1800Z 16.7N 62.5W 40 KT 45 MPH 36H 30/0600Z 18.2N 66.1W 45 KT 50 MPH 48H 30/1800Z 19.7N 69.7W 50 KT 60 MPH 60H 31/0600Z 20.9N 72.5W 50 KT 60 MPH 72H 31/1800Z 22.2N 75.3W 50 KT 60 MPH 96H 01/1800Z 24.7N 79.0W 50 KT 60 MPH 120H 02/1800Z 27.0N 81.0W 45 KT 50 MPH...INLAND $$ Forecaster Brown
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Potential Tropical Cyclone Nine Forecast Discussion Number 1
2020-07-28 16:58:41| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Tue Jul 28 2020 000 WTNT44 KNHC 281458 TCDAT4 Potential Tropical Cyclone Nine Discussion Number 1 NWS National Hurricane Center Miami FL AL092020 1100 AM AST Tue Jul 28 2020 Shower and thunderstorm activity has increased overnight and this morning in association with a broad area of low pressure located several hundred miles east of the Lesser Antilles. Recent visible satellite imagery and ASCAT data show that the system's circulation is quite elongated and lacks a well-defined center. Observations from NOAA buoy 41040 and ASCAT suggest that the system is already producing winds of 30-35 kt, and the systems's initial intensity has been set to 35 kt. Dry air located just to the north of the system has been hindering development over the past couple of days, but environmental conditions are expected to be more conducive for development over the next couple of days. Therefore, the system is likely to become a tropical storm before it reaches the Leeward Islands and advisories are being initiated in order to issue Tropical Storm Warnings for a portion of the Leeward Islands, the U.S. and British Virgin Islands, and Puerto Rico. A U.S. Air Force Reserve reconnaissance aircraft is scheduled to investigate the system early this afternoon, and should provide additional information on the intensity and structure of the low pressure area. It cannot be stressed enough that since the system is still in the formative stage, greater than average uncertainty exists regarding both the short-term and longer-term track and intensity forecasts. A subtropical ridge that extends westward from the central Atlantic is expected to be the dominant steering mechanism over the next several days, and the flow around this ridge should steer the low pressure area generally west-northwestward. However, the details in the track forecast could change depending on exactly where within elongated circulation the center forms. Regardless of the exact track, the system is expected to bring locally heavy rainfall to much of the Lesser Antilles, and tropical-storm-force winds to portions of the Leeward Islands, the Virgin Islands, and Puerto Rico within the next 24-48 hours. After that time, a general west- northwestward heading should continue but as mentioned before, uncertainty exists as to how close the system tracks to Hispaniola, Cuba, the Bahamas, and Florida. The NHC track forecast is in best agreement with the HFIP corrected consensus model. It should be noted that a stronger cyclone is likely to favor a more northern track, while a weaker system is likely to remain more equatorward. Users should remember that the long-term average NHC track forecast errors at days 4 and 5 are 140 and 175 n mi, respectively. Given the current structure of the system, only gradual strengthening is predicted during the next day or two, however the system is expected to become a tropical storm when it is near the Leeward Islands on Wednesday. After 48 hours, possible land interaction with the Greater Antilles, and increasing south to southwesterly shear from an upper-level trough could temper further strengthening. The global models generally weaken the system due to these negative factors and the NHC forecast calls for little change in strength at the longer range. Interests in Hispaniola, the Bahamas, Cuba, and Florida should continue to monitor forecasts as changes to both track and intensity are likely. Key Messages: 1. Potential Tropical Cyclone Nine will produce heavy rains and potentially life-threatening flash flooding and mudslides across the northern Leeward Islands, the Virgin Islands and Puerto Rico. 2. Tropical storm conditions are likely across portions of the Leeward Islands, the Virgin Islands, and Puerto Rico Wednesday through Thursday, and Tropical Storm Warnings are in effect. Do not focus on the details of the track forecast, as rainfall and wind hazards will extend far from the center of the system. 3. The details of the long-range track and intensity forecasts are more uncertain than usual since the system does not have a well-defined center and could move over portions of the Greater Antilles later this week. However, this system could bring some rainfall and wind impacts to portions of Hispaniola, Cuba, the Bahamas, and Florida by the end of the week. Interests there should monitor its progress and updates to the forecast over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 13.8N 53.7W 35 KT 40 MPH...POTENTIAL TROP CYCLONE 12H 29/0000Z 14.8N 56.7W 35 KT 40 MPH...POTENTIAL TROP CYCLONE 24H 29/1200Z 16.0N 60.4W 40 KT 45 MPH...TROPICAL STORM 36H 30/0000Z 17.3N 64.0W 45 KT 50 MPH 48H 30/1200Z 18.8N 67.6W 50 KT 60 MPH 60H 31/0000Z 20.1N 70.7W 50 KT 60 MPH 72H 31/1200Z 21.3N 73.5W 50 KT 60 MPH 96H 01/1200Z 24.1N 77.9W 50 KT 60 MPH 120H 02/1200Z 26.8N 80.6W 45 KT 50 MPH...INLAND $$ Forecaster Brown
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Tropical Depression Hanna Forecast Discussion Number 16
2020-07-26 22:34:20| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Sun Jul 26 2020 000 WTNT43 KNHC 262034 TCDAT3 Tropical Depression Hanna Discussion Number 16 NWS National Hurricane Center Miami FL AL082020 400 PM CDT Sun Jul 26 2020 Surface observations along with radar and satellite imagery show that Hanna continues to weaken as it moves farther inland. There have been no recent observations of sustained tropical-storm-force winds, and Doppler velocities have continued to decrease. Based on these trends, the initial wind speed has been reduced to 30 kt. Hanna should continue to spin down while it moves over the high terrain of northeastern Mexico. The system is forecast to become a remnant low in 12-18 hours, and should dissipate over the mountains of Mexico by late Monday, if not sooner. Hanna is moving west-southwestward or 245/8 kt. The cyclone should continue on this general heading and speed until dissipation occurs. The updated NHC track forecast is again similar to the previous advisory and is close to the dynamical model consensus. This is the last NHC advisory on Hanna. Future information on this system can be found in Public Advisories issued by the Weather Prediction Center beginning at 10 PM CDT, under AWIPS header TCPAT3, WMO header WTNT33 KWNH, and on the web at http://www.wpc.ncep.noaa.gov. Key Messages 1. Heavy rainfall from Hanna has already produced numerous reports of flash flooding across south Texas. Additional heavy rainfall will continue to result in life-threatening flash flooding over south Texas and northern Mexico, and isolated minor river flooding in south Texas. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 25.6N 100.6W 30 KT 35 MPH...INLAND 12H 27/0600Z 25.2N 101.6W 25 KT 30 MPH...INLAND 24H 27/1800Z 25.0N 102.6W 20 KT 25 MPH...POST-TROP/INLAND 36H 28/0600Z...DISSIPATED $$ Forecaster Brown
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