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Potential Tropical Cyclone Ten Forecast Discussion Number 9

2017-08-29 22:32:17| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Tue Aug 29 2017 000 WTNT45 KNHC 292032 TCDAT5 Potential Tropical Cyclone Ten Discussion Number 9 NWS National Hurricane Center Miami FL AL102017 500 PM EDT Tue Aug 29 2017 Visible satellite images indicate that a more well-defined circulation has begun to form east of the Outer Banks, and surface observations indicate that pressures are falling. The low is becoming extratropical, and there is no longer a possibility of it becoming a tropical cyclone. In addition, the associated tropical-storm-force winds that have been occurring to the southeast of the center are limited to marine areas, so this will be the last NHC advisory on this system. Maximum winds are estimated to be 40 kt to the southeast of the center. Baroclinic influences are expected to cause the low to deepen as an extratropical cyclone during the next day or two, and it is forecast to produce sustained hurricane-force winds over the northwestern Atlantic by late Wednesday. Gradual weakening is forecast after 36 hours, and the cyclone is likely to be absorbed by another extratropical system over the north Atlantic by day 5. The low continues to accelerate toward the northeast with an initial motion of 050/21 kt, and it should move even faster toward the northeast or east-northeast across the north Atlantic through day 4, embedded in the mid-latitude westerlies. The track, intensity, and wind radii forecasts incorporate guidance provided by NOAA's Ocean Prediction Center. Strong winds on the northern and western side of a frontal boundary associated with the low are expected to affect portions of the mid-Atlantic coast. As a result, high wind warnings are in effect for coastal sections of northeastern North Carolina, southeastern Virginia, and the eastern shore of Virginia and Maryland through this evening. This is the last advisory issued by NHC, and additional information on this system can be found in High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and available on the Web at http://www.opc.ncep.noaa.gov/shtml/NFDHSFAT1.shtml. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 36.0N 74.3W 40 KT 45 MPH 12H 30/0600Z 37.6N 70.7W 45 KT 50 MPH...POST-TROP/EXTRATROP 24H 30/1800Z 39.3N 65.6W 60 KT 70 MPH...POST-TROP/EXTRATROP 36H 31/0600Z 40.9N 60.0W 70 KT 80 MPH...POST-TROP/EXTRATROP 48H 31/1800Z 42.8N 54.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 72H 01/1800Z 47.4N 41.3W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 02/1800Z 52.0N 25.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 03/1800Z...ABSORBED $$ Forecaster Berg

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Tropical Storm Harvey Forecast Discussion Number 37

2017-08-29 16:59:16| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Tue Aug 29 2017 000 WTNT44 KNHC 291459 TCDAT4 Tropical Storm Harvey Discussion Number 37 NWS National Hurricane Center Miami FL AL092017 1000 AM CDT Tue Aug 29 2017 Heavy rains continue to spread over the Houston area and other locations in southeastern Texas and southern Louisiana, exacerbating what is already a catastrophic flood event. Rainfall totals of nearly 50 inches have been observed at several locations in the Greater Houston area and southeastern Texas. Storm totals could reach higher amounts in some locations, which would be historic for the area. Harvey consists of a vigorous circulation of low clouds with some patches of deep convection well to the north of the center and a cyclonically curved convective band in the eastern semicircle. The initial intensity is kept at 40 kt until we have a more recent estimate when the reconnaissance plane checks the area this afternoon. Strong shear prevails over the cyclone, so no significant change in intensity is anticipated before landfall. A gradual weakening is forecast once the circulation moves inland. The circulation is moving toward the north-northeast or 025 degrees at 4 kt. Harvey is expected to be steered to the northeast with an increase in forward speed by the mid-latitude southwesterly flow ahead of a trough. Most of the guidance is consistent with this solution, and the NHC forecast is in the middle of the guidance envelope. Given that the guidance is tightly clustered the confidence in the track forecast is high. Key Messages: 1. Ongoing catastrophic and life-threatening flooding will continue across southeastern Texas. Additional rainfall accumulations of 6 to 12 inches are expected across the upper Texas coast into southwestern Louisiana, with isolated storm totals as high as 50 inches. Please heed the advice of local officials. Do not attempt to travel if you are in a safe place, and do not drive into flooded roadways. Refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard. A summary of rainfall totals compiled by the Weather Prediction Center can be found at: www.wpc.ncep.noaa.gov/discussions/nfdscc1.html 2. The flood threat has spread farther east into Louisiana. Additional rainfall amounts of 5 to 10 inches are expected in southern Louisiana into coastal Mississippi and Alabama. Please heed the advice of local officials and refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard in these areas. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 28.4N 94.3W 40 KT 45 MPH 12H 30/0000Z 28.8N 94.0W 40 KT 45 MPH 24H 30/1200Z 29.8N 93.4W 40 KT 45 MPH...INLAND 36H 31/0000Z 30.8N 92.8W 30 KT 35 MPH...INLAND 48H 31/1200Z 32.0N 92.0W 30 KT 35 MPH...INLAND 72H 01/1200Z 34.5N 89.5W 25 KT 30 MPH...POST-TROP/INLAND 96H 02/1200Z 36.5N 86.0W 25 KT 30 MPH...POST-TROP/INLAND 120H 03/1200Z 38.5N 81.0W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Avila

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Potential Tropical Cyclone Ten Forecast Discussion Number 8

2017-08-29 16:37:14| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Tue Aug 29 2017 000 WTNT45 KNHC 291437 TCDAT5 Potential Tropical Cyclone Ten Discussion Number 8 NWS National Hurricane Center Miami FL AL102017 1100 AM EDT Tue Aug 29 2017 Surface observations near and offshore the southern coast of North Carolina indicate that an elongated circulation and pressure minimum are located over Onslow Bay, but satellite imagery still shows no signs of a well-defined center. In addition, a sharp wind shift, associated with a front, extends northeastward across Pamlico and Albemarle Sounds and the Outer Banks. Maximum winds remain 35 kt for continuity's sake since there have been no recent observations of sustained tropical-storm-force winds. The disturbance has so far failed to become a tropical cyclone, and since vertical shear is 30-40 kt and increasing, it appears that it now has a low chance of doing so before it becomes extratropical later today. Baroclinic energy from the approaching shortwave trough should cause the extratropical cyclone to strengthen significantly during the next day or two, and it is forecast to be producing hurricane-force winds over the northwestern Atlantic by 36 hours. Gradual weakening is expected after that time until the cyclone is absorbed on day 5. The track, intensity, and wind radii forecasts continue to incorporate guidance provided by NOAA's Ocean Prediction Center. The disturbance is accelerating toward the northeast with an initial motion of 045/15 kt, and it is likely to clear the Outer Banks into the western Atlantic by late this afternoon. The system is embedded in the mid-latitude westerlies, and it will be interacting with a shortwave trough moving east of the Great Lakes during the next couple of days. This will cause the disturbance to continue accelerating toward the northeast or east-northeast over the north Atlantic for the next 4 days. The cyclone is expected to be absorbed by another extratropical low by day 5. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 34.4N 77.2W 35 KT 40 MPH...POTENTIAL TROP CYCLONE 12H 30/0000Z 36.6N 73.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 24H 30/1200Z 38.8N 69.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 31/0000Z 40.4N 63.8W 70 KT 80 MPH...POST-TROP/EXTRATROP 48H 31/1200Z 41.8N 58.4W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 01/1200Z 45.8N 45.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 02/1200Z 51.0N 29.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 03/1200Z...ABSORBED $$ Forecaster Berg

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Potential Tropical Cyclone Ten Forecast Discussion Number 7

2017-08-29 11:01:12| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Tue Aug 29 2017 000 WTNT45 KNHC 290901 TCDAT5 Potential Tropical Cyclone Ten Discussion Number 7 NWS National Hurricane Center Miami FL AL102017 500 AM EDT Tue Aug 29 2017 The disturbance has developed a center that has been trackable this evening though it is still not well-defined, since it appears to be considerably elongated northeast-southwest. The disturbance continues to display very cold, but extremely asymmetric deep convection with all of the thunderstorm activity east of the center due to strong vertical shear. Moreover, the convection is showing no identifiable banding features. So the system is not yet a tropical cyclone. Regardless of the label we use to describe this hybrid system, maximum winds are around 35 kt based upon a Dvorak classification from TAFB and observed winds just below that from the NDBC Buoy 41013. The initial motion of the disturbance is northeast at a faster rate of about 10 kt. Continued acceleration is expected during the next couple of days as a mid- to upper-level trough over the Great Lakes moves closer to the system. The NHC forecast track takes the disturbance across the North Carolina coastline today. By tonight, the cyclone is forecast to move offshore and accelerate over the Atlantic in the mid-latitude westerlies. The NHC track forecast lies near the middle of the guidance envelope and is not substantially changed from the previous advisory. Given the poor organization of the disturbance and the strong wind shear environment that it is embedded within, the chances of this disturbance becoming a tropical cyclone have decreased to about a coin flip. Nonetheless, the potential impacts of tropical-storm- force winds across portions of North Carolina are likely today even if the system does not become a tropical cyclone. The system is expected to become extratropical in 24 hours or less when it interacts with the aforementioned mid- to upper-level trough. Significant strengthening as an extratropical cyclone is forecast for a couple of days due to baroclinic forcing. No significant change has been made to the NHC intensity forecast. The track, intensity, and wind radii forecasts from 24 to 120 h are based on guidance provided by NOAA's Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 33.5N 78.5W 35 KT 40 MPH...POTENTIAL TROP CYCLONE 12H 29/1800Z 35.4N 76.0W 40 KT 45 MPH 24H 30/0600Z 38.0N 71.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 30/1800Z 39.5N 66.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 48H 31/0600Z 41.0N 61.0W 70 KT 80 MPH...POST-TROP/EXTRATROP 72H 01/0600Z 44.5N 50.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 02/0600Z 50.0N 33.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 03/0600Z 55.0N 19.0W 30 KT 35 MPH...POST-TROP/EXTRATROP $$ Forecaster Landsea

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Tropical Storm Harvey Forecast Discussion Number 36

2017-08-29 11:00:43| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Tue Aug 29 2017 000 WTNT44 KNHC 290900 TCDAT4 Tropical Storm Harvey Discussion Number 36 NWS National Hurricane Center Miami FL AL092017 400 AM CDT Tue Aug 29 2017 Heavy rains continue to spread over the Houston area and other locations in southeastern Texas and southern Louisiana, exacerbating what is already a catastrophic flood event. Rainfall totals exceeding 40 inches have been observed at several locations in the Greater Houston area and southeastern Texas. Storm totals could reach 50 inches in some locations, which would be historic for the area. The center of Harvey is moving slowly over the waters of the extreme northwestern Gulf of Mexico, and there continues to be essentially no deep convection near that center. The current intensity is estimated to still be 40 kt based on surface observations from buoys and land stations. Given the lack of central convection and strong south-southwesterly shear over the system, significant restrengthening is not anticipated before the center crosses the coast again within 36 hours or so. Gradual weakening will occur after landfall. Harvey has turned from an east-southeastward to an eastward heading and the initial motion is now about 100/3 kt. The storm should turn northeastward to north-northeastward over the next couple of days as a ridge to the northwest of the system weakens and Harvey is steered around the western side of a ridge to the east. Some further eastward adjustments to the official track forecast were made, following the latest model consensus forecasts. However, it is important not to focus on the exact forecast track since the main threat from Harvey, heavy rain and flooding, can and will occur well removed from the track of the center. Key Messages: 1. Ongoing catastrophic and life-threatening flooding will continue across southeastern Texas. Additional rainfall accumulations of 7 to 13 inches are expected across the upper Texas coast into southwestern Louisiana, with isolated storm totals as high as 50 inches. Please heed the advice of local officials. Do not attempt to travel if you are in a safe place, and do not drive into flooded roadways. Refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard. A summary of rainfall totals compiled by the Weather Prediction Center can be found at: www.wpc.ncep.noaa.gov/discussions/nfdscc1.html 2. The flood threat has spread farther east into Louisiana. Additional rainfall amounts of 5 to 15 inches are expected in south-central Louisiana. Rainfall amounts of 5 to 10 inches are expected in southeast Louisiana and coastal Mississippi and Alabama. Please heed the advice of local officials and refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard in these areas. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 28.1N 94.8W 40 KT 45 MPH 12H 29/1800Z 28.3N 94.5W 40 KT 45 MPH 24H 30/0600Z 28.8N 93.9W 40 KT 45 MPH 36H 30/1800Z 29.9N 93.4W 40 KT 45 MPH...INLAND 48H 31/0600Z 31.1N 92.7W 35 KT 40 MPH...INLAND 72H 01/0600Z 33.7N 90.7W 30 KT 35 MPH...INLAND 96H 02/0600Z 36.0N 87.5W 25 KT 30 MPH...POST-TROP/INLAND 120H 03/0600Z 37.5N 83.5W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Pasch

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