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Potential Tropical Cyclone Three Forecast Discussion Number 3
2021-06-18 10:55:14| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Fri Jun 18 2021 000 WTNT43 KNHC 180855 TCDAT3 Potential Tropical Cyclone Three Discussion Number 3 NWS National Hurricane Center Miami FL AL032021 400 AM CDT Fri Jun 18 2021 The system became a little better organized overnight at the northern end of its associated broad surface trough over the central Gulf of Mexico. Satellite images show increasing deep convection along with more curvature to the low clouds, suggesting that the ill-defined center of this system is trying to re-form farther to the north. Since it still lacks a well-defined center, the system remains a potential tropical cyclone. Recent scatterometer data indicate that winds have increased to at least 30 kt and have grown over a larger area on the east side of the circulation. The initial motion is a highly uncertain 360/12. There is fair agreement that this northward motion, with some re-formation of the center, will continue as the system remains steered by a subtropical ridge to the southeast. The low should then turn northeastward and move across the southeastern U.S. No significant changes were made to the previous track forecast and the guidance is in fairly good agreement. It should also be noted that model "spaghetti" plots are not doing a good job tracking the center of this system, and could give a very misleading impression on the forecast track if used by themselves. There is still a lot of shear over the Gulf of Mexico and that should continue through landfall. However, the system is somewhat hybrid in nature and the shear shouldn't prevent its intensification to a tropical storm later today (possibly with subtropical characteristics). Model guidance is consistent with slow strengthening until landfall, and the new forecast is close to the previous one. After landfall, most of the global models show a strong band of heavy rain and tropical-storm-force winds persisting on the southeastern side. The expected large distance from the center necessitates extending the Tropical Storm Warning into the northwestern Florida panhandle. The system will likely dissipate in about 3 days over the southeastern United States. Given the current and anticipated structure of this system, users should not focus on the exact track of the center, as rainfall and wind hazards are likely to extend well east of the center and arrive well in advance of landfall. Key Messages: 1. The system is expected to produce heavy rainfall, considerable flash, urban and small stream flooding beginning today and continuing through the weekend along the Central Gulf coast with flood impacts spreading northeastward into the Southern Appalachians. 2. Tropical storm conditions are expected to begin today in areas near and well to the east of the center along portions of the central Gulf Coast from Intracoastal City, Louisiana, to the Okaloosa/Walton County line, Florida, including New Orleans. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 25.2N 91.5W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 18/1800Z 27.0N 91.5W 35 KT 40 MPH...TROPICAL CYCLONE 24H 19/0600Z 29.2N 91.2W 40 KT 45 MPH 36H 19/1800Z 31.0N 89.5W 35 KT 40 MPH...INLAND 48H 20/0600Z 32.6N 87.6W 25 KT 30 MPH...INLAND 60H 20/1800Z 34.5N 85.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 21/0600Z...DISSIPATED $$ Forecaster Blake
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Potential Tropical Cyclone Three Forecast Discussion Number 2
2021-06-18 04:38:42| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT Thu Jun 17 2021 000 WTNT43 KNHC 180238 TCDAT3 Potential Tropical Cyclone Three Discussion Number 2 NWS National Hurricane Center Miami FL AL032021 1000 PM CDT Thu Jun 17 2021 Satellite imagery and data from an Air Force Reserve Hurricane Hunter aircraft indicate that the low pressure area over the southwestern Gulf of Mexico has changed little in organization during the past several hours, and the associated convection lies well to the east of the broad and poorly defined center. The initial intensity will be held at 25 kt based partially on ship reports from the northeastern and northern parts of the system. Due to the poorly defined center, the initial motion is a highly uncertain 360/8. The system should move generally northward for the next 24-36 h to a position near the coast of Louisiana, followed by a motion toward the northeast across the southeastern United States as it moves through a weakness in the subtropical ridge caused by an upper-level trough over Texas, northern Mexico, and the adjacent Gulf of Mexico. The forecast track is basically an update of the previous forecast. It should be noted that the latest GFS run continues to forecast a re-formation of the center to the north sometime on Friday, and the forecast forward motion tries to account for this possibility. The aforementioned upper-level trough is causing shear over the system, and present indications are that some shear will persist through landfall and hinder development. The intensity forecast calls for the low to become a tropical cyclone in about 12 h, followed by some modest strengthening to tropical storm strength at 24-36 h. This would be followed by weakening over land, with the system dissipating over the southeastern United States between 72- 96 h. There is a chance that, due to the interaction with the upper-level trough, the system may take on subtropical cyclone characteristics instead of tropical cyclone characteristics. The new intensity forecast is similar to the previous forecast, and it lies at the upper edge of the intensity guidance envelope. Given the current and anticipated structure of this system, users should not focus on the exact track of the center, as rainfall and wind hazards are likely to extend well east of the center and arrive well in advance of landfall. Key Messages: 1. The system is expected to produce heavy rainfall, considerable flash, urban and small stream flooding beginning Friday and continuing through the weekend along the Central Gulf coast, spreading northeastward into the Southern Appalachians. 2. Tropical storm conditions are expected to begin Friday in areas near and well to the east of the center along portions of the central Gulf Coast from Intracoastal City, Louisiana, to the Alabama/Florida border, including New Orleans. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 23.5N 92.2W 25 KT 30 MPH...POTENTIAL TROP CYCLONE 12H 18/1200Z 25.0N 92.4W 30 KT 35 MPH...TROPICAL CYCLONE 24H 19/0000Z 27.2N 92.4W 35 KT 40 MPH 36H 19/1200Z 29.8N 91.1W 40 KT 45 MPH...INLAND 48H 20/0000Z 32.0N 88.8W 30 KT 35 MPH...INLAND 60H 20/1200Z 34.1N 86.1W 25 KT 30 MPH...POST-TROP/INLAND 72H 21/0000Z 35.6N 83.0W 20 KT 25 MPH...POST-TROP/INLAND 96H 22/0000Z...DISSIPATED $$ Forecaster Beven
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Potential Tropical Cyclone Three Forecast Discussion Number 1
2021-06-17 22:34:35| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Thu Jun 17 2021 880 WTNT43 KNHC 172034 TCDAT3 Potential Tropical Cyclone Three Discussion Number 1 NWS National Hurricane Center Miami FL AL032021 400 PM CDT Thu Jun 17 2021 Visible satellite images show that the cloud pattern associated with the broad area of low pressure located over the southwestern Gulf of Mexico is gradually becoming better organized. Deep convection is beginning to form a broad curved band over the eastern portion of the system, similar to what one might see in a developing subtropical cyclone. Although the upper-level winds are not particularly favorable for development, with lots of westerly shear over the area, the global models do suggest tropical/subtropical cyclogenesis within the next 12 hours or so. Given the proximity of the disturbance to land, which requires tropical storm warnings at this time, advisories are being initiated on this system as a potential tropical cyclone. Earlier scatterometer data suggested that the circulation was still rather broad. An Air Force Hurricane Hunter plane is currently investigating the system and has not yet found a well-defined center. Maximum winds based on surface observations and the scatterometer pass are near 25 kt. Numerical intensity guidance do not indicate a great deal of strengthening before the system reaches the coastline, and the official forecast is at the high end of the guidance. Since the center is not that well-defined at this time, the initial motion estimate, 360/8 is quite uncertain. The system is expected to move northward into a weakness in the subtropical ridge for the next day or so and then, after landfall along the central Gulf Coast, turn toward the northeast on the northwest side of a mid-level anticyclone near Florida. The official track forecast is closest to the GFS and ECMWF predictions. It should be noted, however, that these models suggest some reformation of the center near the Louisiana coast rather than just motion from the southwest Gulf to the expected coastal landfall point. Given the current and anticipated structure of this system, users should not focus on the exact track of the center, as rainfall and wind hazards are likely to extend well east of the center and arrive well in advance of landfall. Key Messages: 1. The system is expected to produce heavy rainfall and considerable flash, urban, and small stream flooding beginning Friday and continuing through the weekend along the central Gulf coast and spreading northeastward into the Southern Appalachians. 2. Tropical storm conditions are expected to begin Friday in areas near and well to the east of the center along portions of the central Gulf Coast from Intracoastal City, Louisiana, to the Alabama/Florida border, including New Orleans. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 22.9N 92.4W 25 KT 30 MPH...POTENTIAL TROP CYCLONE 12H 18/0600Z 24.5N 92.5W 25 KT 30 MPH...TROPICAL CYCLONE 24H 18/1800Z 26.5N 92.5W 35 KT 40 MPH 36H 19/0600Z 29.0N 92.0W 40 KT 45 MPH 48H 19/1800Z 31.5N 89.5W 30 KT 35 MPH...INLAND 60H 20/0600Z 34.0N 87.0W 25 KT 30 MPH...INLAND 72H 20/1800Z 35.0N 84.0W 20 KT 25 MPH...INLAND 96H 21/1800Z...DISSIPATED $$ Forecaster Pasch/Brennan
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Post-Tropical Cyclone Carlos Forecast Discussion Number 16
2021-06-16 16:48:08| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Wed Jun 16 2021 000 WTPZ43 KNHC 161448 TCDEP3 Post-Tropical Cyclone Carlos Discussion Number 16 NWS National Hurricane Center Miami FL EP032021 800 AM PDT Wed Jun 16 2021 Shortwave infrared satellite imagery suggests that Carlos's center has become less defined since last evening's scatterometer passes, and the overall circulation is losing definition as it becomes embedded within the Intertropical Convergence Zone (ITCZ). Despite the few sporadic bursts of convection that have been occurring, the system has been unable to generate persistent organized deep convection near its center for quite some time, and Carlos is therefore being designated as a remnant low with maximum winds of 25 kt. Moderate westerly shear and ingestion of drier air should cause the remnant low to weaken further, and likely dissipate within the ITCZ in 2 to 3 days. Geostationary and microwave imagery indicates that Carlos has sunk a little farther south than previously estimated, and its 12-hour heading has been toward the west-southwest (240/6 kt). The bulk of the track models show that the remnant low should resume a westward motion later today and then maintain a steady west to west-northwest heading through Friday, steered by the low-level trade winds. The new NHC official track forecast is a blend of the previous forecast and the GFS-ECMWF consensus, and due to the southward-adjusted initial position, is about a half a degree south of the previous forecast. This is the last advisory on Carlos. For additional information on the remnant low please see High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFEPI, WMO header FZPN02 KWBC, and on the web at ocean.weather.gov/shtml/NFDHSFEPI.php FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 8.6N 135.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 12H 17/0000Z 8.6N 136.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 17/1200Z 8.7N 137.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 18/0000Z 9.0N 138.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 18/1200Z 9.2N 140.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 19/0000Z...DISSIPATED $$ Forecaster Berg
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Tropical Depression Carlos Forecast Discussion Number 15
2021-06-16 10:35:36| National Hurricane Center (East Pacific)
Issued at 1100 PM HST Tue Jun 15 2021 000 WTPZ43 KNHC 160835 TCDEP3 Tropical Depression Carlos Discussion Number 15 NWS National Hurricane Center Miami FL EP032021 1100 PM HST Tue Jun 15 2021 Carlos has maintained a small area of deep convection to the south and northeast of the well-defined low-level center of circulation. However, the convection has decreased in coverage and has become more linear over the past 3 h. Despite the ragged convective appearance in infrared satellite imagery, ASCAT-A/-B passes at 0438Z and 0554Z, respectively, indicated that the small cyclone was still producing winds of 28-29 kt in the northwestern quadrant. Therefore, the intensity is being kept at 30 kt for this advisory. Carlos is moving a little south of due west or 260/06 kt. As per the previous forecast discussion, a gradual westward turn is expected to occur later today, followed by a westward to west-northwestward motion thereafter as the cyclone weakens and becomes more vertically shallow, being steered more by the long-fetch easterly trade wind flow. The new NHC track forecast is essentially just an update of the previous advisory track and lies near a blend of the TVCE and NOAA-HCCA consensus track models. The only positive factor that Carlos has going for it is the warm water beneath the cyclone where sea-surface temperatures (SST) are 27.5 deg C. Surrounding the small cyclone, however, is a very dry and cool airmass, with stable stratocumulus clouds now wrapping into the system, while deep-layer vertical wind shear of more than 20 kt has been increasing from the west. Although SSTs are expected to be warm enough to sustain a tropical cyclone for the next few days, the unfavorable combination of strong shear and a drier airmass is expected to cause Carlos to weaken and degenerate into a remnant low by late today, if not sooner. The NHC intensity forecast is similar to the previous advisory, and closely follows the HCCA and IVCN intensity consensus models. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 9.2N 135.0W 30 KT 35 MPH 12H 16/1800Z 9.2N 135.9W 25 KT 30 MPH 24H 17/0600Z 9.2N 137.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 17/1800Z 9.4N 138.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 18/0600Z 9.6N 139.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 18/1800Z 9.8N 141.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 19/0600Z...DISSIPATED $$ Forecaster Stewart
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