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Hurricane HERMINE Forecast Discussion Number 19

2016-09-02 05:00:27| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT THU SEP 01 2016 000 WTNT44 KNHC 020300 TCDAT4 HURRICANE HERMINE DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 1100 PM EDT THU SEP 01 2016 Reports from an Air Force Reserve Hurricane Hunter aircraft indicate that Hermine has gradually intensified since the last forecast advisory. The plane measured 86-kt flight-level winds southeast of the center at 850 mb with SFMR and dropsonde data suggesting winds of at least 65 kt. Based on these data and a earlier 983 mb central pressure, the initial intensity is set at 70 kt. The initial motion remains 030/12. The flow on the eastern side of a mid-level trough over the southeastern United States should cause Hermine to move north-northeastward to northeastward with an increase in forward speed during the next 36 hours. The track guidance is tightly clustered during this period, and this part of the forecast track is an update of the previous track. At 48 hours and beyond, Hermine is expected to interact with a baroclinic trough over the northeastern United States. The track guidance become rather divergent during this period, with the GFS and ECMWF models showing a looping track close to the coast, while the UKMET and Canadian models show a slow motion somewhat farther offshore. The new forecast track compromises between these solutions and shows a slow northeastward motion during this time. Regardless of the exact track, Hermine should linger for several days near the northeastern U. S. coast as a vigorous low pressure system. A little more strengthening is possible during the last few hours before landfall. After landfall, Hermine is expected to weaken as it crosses the southeastern United States, eventually emerging from the North Carolina coast as a tropical storm. The cyclone is expected to re-intensify as an extratropical low during its interaction with the baroclinic trough. The forecast intensities have been raised for this part of the forecast based on global model forecasts, and it is possible that they are a little conservative. Later in the forecast period, vertical shear decreases, and the cyclone could be situated over marginally warm waters. Therefore there is the possibility of the system regaining some tropical characteristics in 4-5 days, although this remains speculative. KEY MESSAGES: 1. As landfall occurs, it is important to not focus on the exact forecast track. Hermine is an extremely asymmetric storm, with a large extent of dangerous winds, life-threatening storm surge, and flooding rains well to the east and southeast of the path of the center. 2. Hermine is expected to become a post-tropical cyclone while still producing hazardous winds and storm surge over land. NWS policy allows NHC to write advisories on and issue tropical storm watches and warnings for post-tropical cyclones, when the system continues to pose a significant threat to life and property. NHC and the NWS Eastern Region have decided that this option will be invoked for Hermine. After Hermine becomes a post-tropical cyclone, NHC will continue to issue its full suite of advisory and warning products for as long as the system remains a significant threat to land. FORECAST POSITIONS AND MAX WINDS INIT 02/0300Z 29.7N 84.3W 70 KT 80 MPH 12H 02/1200Z 31.5N 82.8W 60 KT 70 MPH 24H 03/0000Z 33.6N 79.7W 45 KT 50 MPH...INLAND 36H 03/1200Z 35.6N 75.7W 45 KT 50 MPH...INLAND 48H 04/0000Z 37.0N 73.2W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 05/0000Z 38.0N 72.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 06/0000Z 39.0N 72.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 07/0000Z 39.5N 70.5W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven

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Hurricane HERMINE Forecast Discussion Number 18

2016-09-01 22:46:59| National Hurricane Center (Atlantic)

Issued at 400 PM CDT THU SEP 01 2016 000 WTNT44 KNHC 012045 TCDAT4 HURRICANE HERMINE DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 400 PM CDT THU SEP 01 2016 Hermine was recently upgraded to a hurricane based on an SFMR-observed surface wind from an Air Force Hurricane Hunter aircraft. The initial intensity is set at 65 kt based on that observation. Satellite images show that the cloud pattern continues to gradually become better organized with more distinct curved bands of showers and thunderstorms, although the system currently lacks concentrated inner-core convection. Hermine has a little more time to strengthen, so the official forecast shows a slight additional increase in intensity before landfall. This is consistent with the latest LGEM guidance. Hermine is forecast to become extratropical at 48 hours when the global models forecast it to become embedded within a frontal zone. Later in the forecast period, vertical shear decreases and the cyclone could be situated over marginally warm waters. Therefore there is the possibility of the system regaining some tropical characteristics in 4-5 days, although this is speculative at this time. Aircraft center fixes indicate that the motion remains 030/12 kt. The flow on the eastern side of a mid-level trough over the southeastern United States should cause Hermine to move north-northeastward to northeastward with some increase in forward speed during the next day so. By 48 hours, the track guidance shows the system slowing down as it begins to interact with a mid-level cutoff vortex over the eastern United States. In 3 days or so, the post-tropical cyclone merges with the cutoff low and a further slowing down of the motion is expected. The official track forecast lies between the latest GFS and ECMWF predictions. KEY MESSAGES: 1. As landfall nears, it is important to not focus on the exact forecast track. Hermine is an extremely asymmetric storm, with a large extent of dangerous winds, life-threatening storm surge, and flooding rains well to the east and southeast of the path of the center. 2. Hermine is expected to become a post-tropical cyclone while still producing hazardous winds and storm surge over land. NWS policy allows NHC to write advisories on and issue tropical storm watches and warnings for post-tropical cyclones, when the system continues to pose a significant threat to life and property. NHC and the NWS Eastern Region have decided that this option will be invoked for Hermine. After Hermine becomes a post-tropical cyclone, NHC will continue to issue its full suite of advisory and warning products for as long as the system remains a significant threat to land. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 28.5N 85.0W 65 KT 75 MPH 12H 02/0600Z 30.2N 83.9W 70 KT 80 MPH 24H 02/1800Z 32.4N 81.6W 50 KT 60 MPH...INLAND 36H 03/0600Z 34.5N 78.2W 45 KT 50 MPH...INLAND 48H 03/1800Z 36.3N 75.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 04/1800Z 38.0N 72.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 05/1800Z 38.5N 71.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 06/1800Z 39.5N 70.5W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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Hurricane GASTON Forecast Discussion Number 41

2016-09-01 22:35:30| National Hurricane Center (Atlantic)

Issued at 500 PM AST THU SEP 01 2016 000 WTNT42 KNHC 012035 TCDAT2 HURRICANE GASTON DISCUSSION NUMBER 41 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 500 PM AST THU SEP 01 2016 The eye of Gaston is no longer visible in geostationary imagery, which shows the coldest convective tops are located west and north of the center. Dvorak classifications have decreased to T3.5/4.5 from TAFB and T3.0/4.0 from SAB. Based on the winds seen in the earlier ASCAT data, the initial intensity is lowered conservatively to 70 kt for this advisory. Steady weakening is forecast as Gaston is moving over waters below 26C and in an environment of 20-30 kt of southwesterly shear. The NHC forecast is a little lower than the previous one following the trend of all the guidance. Gaston should become post-tropical in about 48 hours and dissipate shortly thereafter. The hurricane has accelerated east-northeastward this afternoon, with an initial motion estimate of 075/25. The track model guidance is in good agreement showing Gaston continuing east-northeastward with a decrease in forward speed as the system weakens and decouples from the mid-level flow. The new NHC track forecast is basically an update of the previous one and is very close to the latest multi- model consensus aid TVCN. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 38.3N 37.5W 70 KT 80 MPH 12H 02/0600Z 38.9N 34.5W 60 KT 70 MPH 24H 02/1800Z 39.5N 30.9W 50 KT 60 MPH 36H 03/0600Z 40.3N 27.9W 40 KT 45 MPH 48H 03/1800Z 41.6N 25.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 04/1800Z...DISSIPATED $$ Forecaster Brennan

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Tropical Storm HERMINE Forecast Discussion Number 17

2016-09-01 19:08:56| National Hurricane Center (Atlantic)

Issued at 1200 PM CDT THU SEP 01 2016 000 WTNT44 KNHC 011708 TCDAT4 TROPICAL STORM HERMINE SPECIAL DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 1200 PM CDT THU SEP 01 2016 Reports from a hurricane hunter aircraft indicate that the extent of tropical-storm-force winds has increased significantly in the eastern semicircle. This requires an extension of the tropical storm warning southward along both Florida coasts. This Special Advisory is being issued to modify the warnings, and to update the analyzed and forecast wind radii. KEY MESSAGES: 1. It is important to not focus on the exact forecast track. Hermine is an extremely asymmetric storm, with a large extent of dangerous winds, life-threatening storm surge, and flooding rains well to the east and southeast of the path of the center. 2. Hermine is expected to undergo a complex interaction with a frontal system when it reaches the Carolinas over the weekend. It is a little early to say what the specific impacts will be for the mid-Atlantic and northeastern states. FORECAST POSITIONS AND MAX WINDS INIT 01/1700Z 27.8N 85.6W 60 KT 70 MPH 12H 02/0000Z 29.0N 84.8W 65 KT 75 MPH 24H 02/1200Z 31.1N 82.9W 50 KT 60 MPH...INLAND 36H 03/0000Z 33.1N 80.0W 45 KT 50 MPH...INLAND 48H 03/1200Z 35.2N 76.7W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 04/1200Z 38.0N 72.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 05/1200Z 38.5N 71.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 06/1200Z 39.5N 70.5W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch/Franklin

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Tropical Storm HERMINE Forecast Discussion Number 16

2016-09-01 17:00:25| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT THU SEP 01 2016 000 WTNT44 KNHC 011500 TCDAT4 TROPICAL STORM HERMINE DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 1000 AM CDT THU SEP 01 2016 Hermine is gradually becoming better organized, with convective banding developing over the eastern semicircle of the circulation. Upper-level outflow continues to be restricted to the northwest of the storm by a cyclonic shear axis depicted by water vapor imagery. The current intensity is set at 55 kt in agreement with SFMR-observed surface winds from an Air Force Hurricane Hunter aircraft. The intensity forecast continues to show Hermine becoming a hurricane before landfall which is in general agreement with the numerical guidance. The global models show Hermine embedded within a frontal zone by 48 hours, so the forecast shows the system becoming extratropical at that time. There is some concern about the evolution of the post-tropical cyclone later in the forecast period, since the shear starts decreasing after 72 hours. This could allow the system to reacquire some tropical characteristics in 4-5 days, although it is not certain how close to the coast the cyclone will be by that time. Based on Hurricane Hunter aircraft fixes and a dropsonde from the NASA Global Hawk aircraft, the initial motion is estimated to be 030/12 kt. A mid-tropospheric trough should steer the system north-northeastward to northeastward for the next couple of days. Later in the forecast period, a developing mid-level cutoff low near the northeast United States coast will cause a slowing of the forward speed as the cyclone interacts with the low. The official forecast track is essentially a blend of the latest GFS and ECMWF solutions, with the former model showing a track closer to the northeast coast and the latter taking the system farther offshore. KEY MESSAGES: 1. It is important to not focus on the exact forecast track. Hermine is a rather asymmetric storm, with a large extent of dangerous winds, life-threatening storm surge, and flooding rains well to the east and southeast of the path of the center. 2. Hermine is expected to undergo a complex interaction with a frontal system when it reaches the Carolinas over the weekend. It is a little early to say what the specific impacts will be for the mid-Atlantic and northeastern states. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 27.4N 86.0W 55 KT 65 MPH 12H 02/0000Z 29.0N 84.8W 65 KT 75 MPH 24H 02/1200Z 31.1N 82.9W 50 KT 60 MPH...INLAND 36H 03/0000Z 33.1N 80.0W 45 KT 50 MPH...INLAND 48H 03/1200Z 35.2N 76.7W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 04/1200Z 38.0N 72.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 05/1200Z 38.5N 71.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 06/1200Z 39.5N 70.5W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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