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Tropical Storm Harvey Forecast Discussion Number 2
2017-08-17 22:49:02| National Hurricane Center (Atlantic)
Issued at 500 PM AST Thu Aug 17 2017 000 WTNT44 KNHC 172048 TCDAT4 Tropical Storm Harvey Discussion Number 2 NWS National Hurricane Center Miami FL AL092017 500 PM AST Thu Aug 17 2017 An Air Force Reserve Hurricane Hunter aircraft found a well-defined circulation in the low pressure area east of the Lesser Antilles, with the center near a cluster of sheared, but strong, convection. The aircraft data suggest that the maximum winds are near 35 kt and that the central pressure is near 1004 mb. Based on these data, the disturbance is upgraded to Tropical Storm Harvey. The initial motion is 270/16. There is no change to the forecast philosophy since the previous advisory. A deep-layer ridge to the north of the system should steer it quickly just north of due west through the forecast period, with this motion expected to bring the system through the Lesser Antilles and into the eastern Caribbean Sea in 12-24 h, into the central Caribbean by 48-72 h, and to the western Caribbean by 96-120 h. One adjustment is that the 96-120 h points have been nudged a little southward in response to a shift in the guidance, and thus now lie closer to Central America than on the previous forecast. The forecast track again lies near the center of the tightly clustered guidance envelope and the various consensus models. The system is in an area of moderate easterly vertical shear, and the large-scale models suggest that light/moderate shear should continue through at least 72 h. The conflicting forecast scenarios alluded to in the previous advisory remain, with the SHIPS and LGEM models still showing steady intensification while the GFS and ECMWF models still forecast degeneration to an easterly wave over the central Caribbean. The new intensity forecast again follows the trend of the SHIPS/LGEM models, but it remains on the low side of the guidance envelope out of respect for the GFS/ECMWF. The 96-120 h intensities have been decreased a little due to the forecast track showing more land interaction. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 13.0N 55.8W 35 KT 40 MPH 12H 18/0600Z 13.1N 58.3W 35 KT 40 MPH 24H 18/1800Z 13.4N 61.6W 40 KT 45 MPH 36H 19/0600Z 13.7N 65.1W 45 KT 50 MPH 48H 19/1800Z 14.0N 68.8W 45 KT 50 MPH 72H 20/1800Z 14.5N 76.5W 55 KT 65 MPH 96H 21/1800Z 15.5N 83.5W 60 KT 70 MPH 120H 22/1800Z 17.0N 88.5W 55 KT 65 MPH...INLAND $$ Forecaster Beven
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Post-Tropical Cyclone Gert Forecast Discussion Number 20
2017-08-17 22:39:21| National Hurricane Center (Atlantic)
Issued at 500 PM AST Thu Aug 17 2017 000 WTNT43 KNHC 172039 TCDAT3 Post-Tropical Cyclone Gert Discussion Number 20 NWS National Hurricane Center Miami FL AL082017 500 PM AST Thu Aug 17 2017 Gert is now post-tropical. The circulation has become quite elongated, and the remaining deep convection appears to be primarily associated with frontal boundaries. A pair of late-arriving ASCAT passes from around 1300 and 1400 UTC indicated that Gert was weaker than previously estimated. Based on the ASCAT data, the initial intensity has been lowered to 55 kt. The initial wind radii were also adjusted based on the ASCAT data. The initial motion estimate is a brisk 060/34 kt. Gert should move quickly northeastward for the next 12 to 24 h while gradually spinning down. After that time, it should slow down and turn more toward the north while merging with or being absorbed by another extratropical low. The track, intensity, and wind radii forecasts have incorporated guidance from NOAA's Ocean Prediction Center. Swells from Gert should continue to affect the coast of the northeastern U.S. and Atlantic Canada through tonight. These swells are likely to produce dangerous surf and rip current conditions. Please consult products from your local weather forecast office for more information. This is the last NHC advisory on Gert. 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 17/2100Z 44.8N 46.0W 55 KT 65 MPH...POST-TROPICAL 12H 18/0600Z 47.8N 40.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 24H 18/1800Z 50.6N 36.2W 40 KT 45 MPH...POST-TROP/EXTRATROP 36H 19/0600Z 52.5N 35.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 48H 19/1800Z...DISSIPATED $$ Forecaster Zelinsky
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Potential Tropical Cyclone Nine Forecast Discussion Number 1
2017-08-17 16:40:26| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Thu Aug 17 2017 000 WTNT44 KNHC 171440 TCDAT4 Potential Tropical Cyclone Nine Discussion Number 1 NWS National Hurricane Center Miami FL AL092017 1100 AM AST Thu Aug 17 2017 Satellite imagery, including experimental 1-minute data from GOES-16, indicates that the circulation of the low pressure area east of the Lesser Antilles is becoming better defined, and that a cluster of strong convection has formed just west of the center. Based on this and the potential for the system to become a tropical storm before reaching the Lesser Antilles, advisories are being initiated as a potential tropical cyclone. An Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate the system this afternoon, and it is likely the aircraft will find a tropical cyclone has formed. The initial motion is 270/15. A deep-layer ridge to the north of the system should steer it generally just north of due west through the forecast period, with this motion expected to bring the system through the Lesser Antilles and into the eastern Caribbean Sea in 24-36 h, into the central Caribbean by 72 h, and to the western Caribbean by 96-120 h. The forecast track lies near the center of the tightly clustered guidance envelope and lies near the various consensus models. The system is in an area of moderate easterly vertical shear, and the large-scale models suggest that light/moderate shear should continue through the forecast period. This seems favorable for strengthening, and the SHIPS and LGEM models show slow, but steady, intensification. However, the GFS and ECMWF models forecast the system to degenerate to an easterly wave over the central Caribbean Sea, possibly due to dry air entrainment. The intensity forecast follows the trend of the SHIPS/LGEM models, but it respects the GFS/ECMWF forecasts by being on the low side of the intensity guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 13.1N 54.1W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 18/0000Z 13.1N 56.4W 30 KT 35 MPH...TROPICAL DEPRESSION 24H 18/1200Z 13.2N 59.8W 35 KT 40 MPH 36H 19/0000Z 13.5N 63.2W 40 KT 45 MPH 48H 19/1200Z 13.9N 66.7W 45 KT 50 MPH 72H 20/1200Z 14.5N 74.5W 55 KT 65 MPH 96H 21/1200Z 15.5N 82.0W 65 KT 75 MPH 120H 22/1200Z 17.0N 87.5W 65 KT 75 MPH $$ Forecaster Beven
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Hurricane Gert Forecast Discussion Number 19
2017-08-17 16:34:45| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Thu Aug 17 2017 000 WTNT43 KNHC 171434 TCDAT3 Hurricane Gert Discussion Number 19 NWS National Hurricane Center Miami FL AL082017 1100 AM AST Thu Aug 17 2017 The convective structure of Gert has rapidly deteriorated during the morning hours due to very cold SSTs and vertical wind shear exceeding 40 kt. The hurricane still has a little deep convection in the northeast quadrant, but the low-level circulation appears to have become somewhat elongated along a south-southwest, north-northeast axis. Subjective Dvorak classifications from TAFB and SAB have decreased, and the initial intensity has been decreased accordingly, to 70 kt. Since there is a lack of recent scatterometer or buoy observations near the center, the intensity estimate is a little more uncertain than normal. Gert continues to accelerate toward the northeast and the initial motion estimate is 060/35 kt. Very little change has been made to the track or intensity forecast. The cyclone is quickly becoming extratropical, and the transition process should complete later today. Gert should continue to steadily spin down while moving quickly toward the northeast for the next day or so ahead of a large extratropical low currently centered near the Gulf of St. Lawrence. An interaction of the two cyclones should result in the eventual absorption or dissipation of Gert shortly after 48 h. The track, intensity, and wind radii forecasts have incorporated guidance from NOAA's Ocean Prediction Center. Swells from Gert should continue to affect the coast of the northeastern U.S. and Atlantic Canada through tonight. These swells are likely to produce dangerous surf and rip current conditions. Please consult products from your local weather forecast office for more information. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 43.2N 50.0W 70 KT 80 MPH 12H 18/0000Z 46.0N 43.6W 55 KT 65 MPH...POST-TROP/EXTRATROP 24H 18/1200Z 49.3N 37.4W 45 KT 50 MPH...POST-TROP/EXTRATROP 36H 19/0000Z 51.3N 35.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 48H 19/1200Z 52.4N 34.3W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 20/1200Z...DISSIPATED $$ Forecaster Zelinsky
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Hurricane Gert Forecast Discussion Number 18
2017-08-17 10:37:13| National Hurricane Center (Atlantic)
Issued at 500 AM AST Thu Aug 17 2017 000 WTNT43 KNHC 170837 TCDAT3 Hurricane Gert Discussion Number 18 NWS National Hurricane Center Miami FL AL082017 500 AM AST Thu Aug 17 2017 The expected weakening trend of Gert appears to have started. The eye of the hurricane is no longer evident in satellite images, and the convective pattern has become less symmetric during the past several hours. The initial wind speed is lowered a little to 85 kt, in agreement with a blend of the Dvorak final T- and CI-numbers from TAFB and SAB. The hurricane is crossing the north wall of the Gulf Stream current, and it will soon be moving over substantially colder water. These colder waters combined with a significant increase in wind shear and drier air should cause rapid weakening during the next day or so. Gert is now forecast to lose its tropical characteristics in about 24 hours, when it will be over very cool sea surface temperatures of about 16 deg C. The NHC intensity forecast is an update of the previous one, and it generally follows the GFS model. Gert is embedded in fast mid-latitude flow and it is racing east-northeastward over the central Atlantic at 34 kt. A decrease in forward speed and a slight turn to the northeast is expected during the next couple of days while Gert interacts with a large extratropical low to the east of Atlantic Canada. The global models show this extratropical system absorbing, or merging with, Gert in about 3 days. The NHC track forecast is adjusted a little to the right of the previous one to come into better agreement with the latest consensus models. The track, intensity, and wind radii forecasts have incorporated guidance from NOAA's Ocean Prediction Center. Swells from Gert should continue to affect the coast of the northeastern U.S. and Atlantic Canada through tonight. These swells are likely to produce dangerous surf and rip current conditions. Please consult products from your local weather forecast office for more information. FORECAST POSITIONS AND MAX WINDS INIT 17/0900Z 41.7N 54.0W 85 KT 100 MPH 12H 17/1800Z 44.2N 47.4W 70 KT 80 MPH 24H 18/0600Z 48.0N 40.2W 55 KT 65 MPH...POST-TROP/EXTRATROP 36H 18/1800Z 50.7N 36.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 19/0600Z 52.0N 33.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 20/0600Z...DISSIPATED $$ Forecaster Cangialosi
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